Tuesday, December 22, 2009

Super Stock Ciao

The lowly Vespa Ciao is one of the most elegantly designed motor vehicles ever produced. Truly the 'volkswagen beetle' of mopeds, its simple, rugged, compact, and designed for cheap mass production. Its no wonder the tuning scene in Europe has gone completely bonkers for these bikes. The parts, knowledge, and resources available for these dwarfs even the mighty puch. Being knocked-off in India doesn't hurt either, making this the most produced, cheapest, and simplest moped powerplant ever.

Ever since I picked up this low-mile rigid Ciao, I knew it was a vehicle with massive potential. TreatsHQ declared 2008 the year of the Ciao with a flood of vespa parts, and I was itching, but other projects took center stage, and it got shipped all over Wisconsin as my beat-around loaner bike. Two years came and went until about a month ago when I decided to set it up for my girlfriend, because what's better than pretty girls on Ciaos? Pretty girls on ridiculously fast Ciaos! (especially when they are stock and embarassing kitted bikes)

The Ciao's massive potential lies in its unique induction system. Rotary-valve induction is different from piston-port and reed-valve induction, in that the opening and closing of the intake valve is controlled by a mechanical valve, usually a disc on the end of the crankshaft, that opens and closes with the rotation of the engine. The rotary valve offers the low flow-resistance of a piston port, with the asymmetrical timing of the reed valve, for a 'best of both worlds' situation. The main drawback to rotary valve induction is the extra cost of the mechanical hardware which forms a tight seal, and extra complexity. Vespa engineers, however, solved this problem by incorporating a recessed area into the crankshaft web, and placing the port on the back of the crankcase where it would be covered and uncovered by the rotating crank web. Genius!

Seeing as this is the only moped made with this style of induction (aside from a few rare Kriedler models) I wanted to see what could be done in the way of unleashing the potential of the rotary valve. Rather than piston ports which just offer two dimensions of tuning (duration and area- time/area) and reed valves which are pretty boring (bigger=faster, yawn!) the rotary valve allows for tuning of duration, advance, area, and in the specific case of the vespa there is a lot of room for improvement. I started the tuning process by researching and studying the rotary valve system itself, and based the entire performance build around the idea that tuning for certain intake characteristics could yield high torque across a wide powerband, with maximum power in the mid-upper mid range. Two years gave me a lot of time to study and think about the improvements I wanted to make, and my research had already yielded a pretty conclusive game plan before I removed the first screw.

Valve Modifications:
Starting with the rotary valve, the geometries of the parts themselves can be improved for flow, specific opening and closing characterisitcs, etc. Looking at the assembly in 3-d, the passage of air from the carb inlet to the cylinder is hampered at any number of places, most likely due to manufacturing considerations. Right away the inlet 'manifold' nipple that the carb clamps onto is much too small to flow enough air. The rotary valve is very efficient, and capable of extremely high intake velocities, so the carbureation can remain relatively conservative, but there is no reason not to maximize the size of the intake tract. The largest I could bore the front half of the Dellorto SHA 12:10 carb out to was close to 14 mm. To maintain the integrity of the nipple inlet, i went to a more conservative 13-something for the nipple, and to match, the back-half of the carb. This was reamed far enough in, that the rest of the porting in the intake port could be smoothed for minimal flow disturbance.

The 'pencil grinder' which is a tiny little pneumatic 1/8" shaft grinder I bought at harbor freight, is invaluable for this stuff. I could actually stick the whole grinder right in the intake hole for the finish work. I left things a little rough because I really dont care that much about making it look good. A slight bit of surface roughness can actually improve flow characteristics if you are dealing with a convoluted shape, but to be honest, I'm just too lazy for all that tiny grinder bit junk. As you can see, I've opened the port up just about as big as i can safely go. The edges are round, because anytime you flow through a square tube, you basically have no flow in the corners anyhow, and this will make the transition easier and prevent any weird eddy-current crap. The primary concern is not breaking the seal made by the crankshaft web on the ground smooth surface around the port. Opening it up 'all the way' like this is only going to change your intake timing by a matter of a couple degrees and this engine is already absurdly conservative in porting.

Because the crankshaft serves as the rotary valve, opening and closing this port, the modifications made to it, directly translate into the modifications made to the port timing in the cycle. To calculate this, in degrees, just measure the diameter, dummy. I used a paper strip wrapped around the crank web, then i double-checked using the diameter, because the paper couldn't be tight or it would shortcut the recessed area of the crank web. Simple geometry will get you into radians of port timing, then degrees if you prefer. I'm not going to share all this, because I think this might be a competitive bike in stock cylinder racing, and I want a leg up on y'all, but if you really want to copy me you can probably figure it out from the picture. I also added some 'flow improvements' to the open area, sortof like knife-edging but in multiple dimensions.

Man grinding on that hardened steel is a real pain-in-the-butt. I still have slivers all up in my fingers. Brutal. The results are well worth it however, the modifications to the intake tract like this can easily out-flow a smallish 4-petal reed. Just think about how much flow area there is while this port is open! Compare that to four little slits 1/8 by 1/2 inches. Not to mention the fact that no energy of the incoming air is being lost opening the valve. We're talking about serious flow here, from a 13mm carb. Exciting!

To finish everything up, I ground out the transfer ports to match the modifications to the cylinder (which we'll talk about later) and to ensure smooth flow between the back of the crank-case and the transfer ports. Its hard to imagine how this all works in three-dimentional space, but I think I was able to clean everything up for a small improvement. I ported the case about as big as I felt comfortable, so if this engine ever does end up with a kit, it wont have to be rebuilt.

Disassembling and reassembling these cases is the nicest piece of cake in the entire moped tuning world. We're talking easier-than-legos easy. Heated bearings, dropped them on, heated cases, plopped it all together with a nice brown-paper-bag gasket and a few dabs of sealant. I splurged for the nicer bearings and seals from my friends at Allied Bearing(still cheaper than the moped shops) because I have a feeling this engine will have the ever-loving piss revved out of it, and I want it to be reliable for many years of blasting.

Cylinder Porting

To say the stock porting is restrictive is an understatement. I took a port tracing to start with, and was very confused by the results. The port map i traced showed the bottom of the exhaust port was 46 mm from the deck. A lot of very slow stock bikes (cough, Batavus, cough) have a ridiculously high deck height, making the piston come a few mm short of the deck at TDC. This drops the compression dramatically and gives you that nice speed restriction Iowa tuners and 'Scared Mommy' magazine are always raving about without having to make pesky tooling changes. I figured this is what was going on, and the wear pattern from the rings seemed to agree, coming well short of the top, so I proceeded to calculate my new port map assuming the bottom of the exhaust was BDC. Once I got everything together, however, I realized the real reason for the discrepancy was due to the piston coming up and covering 3 mm of the exhaust port at BDC.

This is huge

For 3 mm of the already tiny exhaust port to be covered at BDC is shocking to say the least. Correcting this massive error alone could account for an additional 5-10 mph on a stock bike. Its the same thing as raising a stock exhaust port 3 mm, not to mention the transfer ports, which are level with the exhaust on the bottom. To correct this error, I machined a whole 3.25mm off the top of the stock piston, along the edges, leaving more material in the top of the crown to effectively create a 'squish band' between the stock head and the modified piston.
This will drop the edge of the piston to the proper placement for the exhaust port timing, but will cause the piston to rest a full 4 mm below the deck height. I solved this problem with an iron fist. More accurately, the facing mill, which I have now nicknamed the 'iron fist' as it has proven itself to be an invaluable and dangerously aggressive tool for dealing with these sorts of things.
As you can see, the casting wasn't machined on center, but the milling was done true to the cylinder base face, so it should be accurate, not that it really matters all that much for this. Four millimeters is quite a bit, and what you see left of the top fin, is thin enough to slice tomatoes... which reminds me of an infomercial.

Once the cylinder and piston agreed with my theoretical port map, I did a little math and came up with a port map to highlight the strengths of this little machine. Since this is all for my girlfriend to have a nice, cute, reliable bike she can ride with the gang, I didn't want to make it too crazy, but it would have to keep up with the rest of the Cranks at 35-40 mph. The Ciao is so light, and geared so low, that torque isn't as critical as mid to top end power, plus the Tecno Circuit is a pretty torquey pipe. I also have a lot of faith in the stock single-speed dry clutch. Its simple and easy to get/make parts for, so I figure I can sacrifice some low end if I lighten/tighten up that clutch. The rotary valve was designed, along with the pipe, and the cylinder, to start pulling hard around 2-3k rpm, and hang on up to 8-9k. I went pretty huge with the exhaust and transfers, because I know that pipe will keep the low end manageable, and I wanted to have a little bit of power on the top end when the pipe is starting to poop out. I'll probably keep stock gearing for daily riding, but the plain ol' pulley makes it really easy for me to alter the 'gearing' with a short trip to the machine shop, so I might play with that a bit depending on what the GF likes.

The transfers on this engine leave a lot to be desired, and present a serious challenge for the tuner, because there just isn't any room around them to open them up conventionally. Everything has to stay symmetrical for proper scavenging, and that means getting into the two interfering studs next to the exhaust and the one transfer. To lay things out, the studs were drawn into the port map, and I started measuring. The exhaust port is off-center in relation to the transfers. For a moderate build, it could be widened 4 mm on one side (away from the stud, thank god) and probably make 90% of the performance gain my build is going to see. To push it a bit farther, I went even bigger with the exhaust, and bigger with the transfers, shifting them all away from the offending stud near the exhaust. The Transfers couldn't go out much, but they had a few mm to go in, by removing the absurdly thick cylinder skirt and making them 'finger' or fully open ports. I like to be precise about these things, so I took the cylinder into the machine shop and roughed out the ports. I also added a 3rd transfer 'boost' port in between the two gudgeon pins opposite the exhaust. This is directly adjacent to the third stud, so it couldn't be very deep away from the piston, but the boost port doesn't need to be very large to have a huge impact directing and energizing the air out the exhaust port. This should really liven up the 5k-7k rpm range where the pipe is starting to come off its powerband, and give a lot better torque on the bottom before the pipe is hitting. This is the cylinder back from the machine shop, rough, but the important stuff is all there.

The exhaust nipple was also reamed out as large as I felt I could go before compromising the integrity of the metal. I'm kindof touchy about exhausts, because of bad experiences with my Sachs, and dont like to take chances. At this point I still didnt have the pipe so I couldn't match them, but it turned out to be very close.

Once things were roughed out in the machine shop, it was grinder time. A lot of it. Probably about 5 hours total behind the grinder cleaning up the transfers, booster, and cases to make sure everything matches.

Still pretty rough

Getting a lot better

Finished.. with a custom-made base gasket, felt rubber for maximum sealage.

Whew, thank god for photo montage, that would have taken all day

After finishing up the cylinder, and cleaning everything up really thoroughly, the head was bolted back on and i did a quick compression test. I didn't take any photos of the embarassment, but I think my face mill left things a bit too rough, because I had to use a modified puch aluminum gasket and a tiny bit of goop to hold it in place. Ugh, i hate gasket goop, oh well, things seal great now. Torquing those 3 7mm nuts is very touchy, if they are just the slightest bit off they are real prone to leaky nonsense. Who uses three studs? Whatever.

Frame and other such necessary junk.
As much as I hate to admit it, moped engines actually have to go into frames at some point to realize their true potential. I guess that part just doesn't interest me much. Once the engine was back together, and the electronics were re-installed, I slapped it back in the bike. The wiring was a mess from a previous owner, but I had to redo most of it anyways because full-rigid wasn't going to cut it for a daily driver. As much as I love the ciao's aesthetics, either springer front or rigid, they are both almost un-rideable on Milwaukee's war-torn roads. After doubling the speed, I didn't feel very good about putting my girlfriend on something even I had trouble controlling, so I started trying to find different forks. I had a pair of maxi, garelli, and hobbit forks laying around, all of which I tried. The Hobbit forks seemed to be the best fit for size, looks, etc, and they have the same threads as the top nut from the garelli forks which uses the same 'outside' bearing as the vespa forks. Bingo. The tube was the perfect length for the ciao, but not big enough to fit the post style handlebars. Blah blah, boring stuff. Wiring, handlebars, brackets for the headlight. Not done here, but you can see it coming together.

Running with the pipe on.

First start went perfectly. Fired on the first kick, jetting was correct for my basement. No funny business. I adjusted the timing a bit, initially I retarded it a bit from stock because of the porting, but after running it a bit, it seems like stock timing works best. The cold streak we've been having has prevented me from getting out and test-running it, but it pulls really hard on the stand... cant wait until I finish my brake dyno. More results and pictures of finished bike to come!


First ride on the bike was kinda lousy actually. It was on a very cold day at the beginning of January, and the jetting was way too lean, no power whatsoever, and super boggy. I brought it back in and adjusted the timing, which for some reason was way off, possibly didn't press the foot down enough when gapping. I made a quick hi-flow air filter to richen it up.

The finished bike came out pretty clean, I had to make some headlight brackets.

Here it is all done.

I'm really serious about clean engine bays, wire routing, cables, etc.

So, fast forward a couple weeks, the nice weather yesterday was just too much, I finally got out again on the bike and got a chance to wind her out a bit on lincoln memorial drive. The results are sortof dissapointing. Only 43 mph top speed on the flat, but it picks up to 46 on the down hill (a bit too fast for a rigid if you ask me). I think the compression is too low. I never did actually turn down the head, so i might still have to do that. Also the questionable rings I re-used might be weak. Also the warm weather threw my jetting off again, and now its too rich.

I'm really not happy with the low end either, before the pipe hits, it has no power whatsoever. I know I need to tune up the clutch quite a bit, but there should still be more torque than there is. Correct jetting, finer timing adjustments, and some serious clutch tuning will all be conducted as soon as i have some time. Stay posted for more awesome.

Sunday, December 20, 2009


So the chainsaw article put me over the top, couldn't keep this little chunk of the internet quiet anymore, so I announced to the MA performance tuning forum, that this is what i've been up to for the last month or so.

Thanks a bunch to everyone who has put up supportive comments, and all my new 'followers.' Knowing people are reading this should motivate more frequent and better posts. Check out the new one on port mapping, and check back for the rest of the writeup on the Ciao. Its getting pretty out of control adding additional boost ports and really pushing the limits of that bizarre little motor. Some midwest moped racing is in the works, and even though its at a disadvantage without a variator (i'm not putting one on, either) it should be pretty dangerous with a powerful engine and light weight.

Also, props to 1977 Mopeds who mentioned this on their facebook. Check out their blog and buy some stuff, cheapass!

Port Mapping

Most of the people who have gotten hooked on mopeds have come into this hobby as their first foray into mechanics. As amateurs, their approach to tuning takes various routes, but sooner or later the inquiring tuner discovers the power of cylinder porting. The port map, or the placement and size of the ports where they contact the face of the cylinder, serves as the 'brain' of the engine, and a little grinding can have tremendous impact on the characteristics of the engine. My first investigation into porting took an artistic approach, borrowing more skills from my jewelry training than my engineering training. Grinding a half millimeter at a time can yield impressive results, and provides excellent practical experience in what affects what, but as the budding tuner's skill and sophistication improve, a higher level of accuracy is necessary to push the ragged edge of performance. Planning a port map and transferring it accurately to the cylinder, so the physical ports come out the same as the theoretical model you designed, is key to pushing a cylinder to its limits.

For this article, I'll be demonstrating the process I use to create and transfer a port map. I'll be using a stock vespa cylinder which i'm planning drastic changes to. I'll have the full write up on this project done in a couple weeks.

Creating the stock (initial) port map:

To modify the porting accurately, its important to start by determining the initial port map. The easiest way to do this is by 'tracing' the ports, the same as you would take a rubbing of a texture or relieved letters. I start by cutting a rectangular piece of paper approximately the size of the internal surface of the cylinder. Apply a piece of masking tape along one of the sides and roll the paper into a tube. When you put it inside the cylinder, make sure the top edge is perfectly aligned with the top of the cylinder and the paper is fitting tight to the cylinder. You want the paper to perfectly mimic the surface of the cylinder wall.

From cylinder blueprint
If you want to secure it in place with a piece of tape reaching up onto the head mating surface, it might help it from sliding around as you trace. You will want the seam to be away from any of the ports. Now take a pencil, and sketch over the edges of the ports.
From cylinder blueprint
Sketch the border of the paper also, to give you an idea of the actual dimensions, then remove the paper.

Now that you have your port map sketch, go along the port edges with pen or pencil and flush them out. Take your calipers and dimension the ports. The bottom edge of the exhaust is typically 'bottom dead center' and is more important than the top edge. Many cylinders, especially on stock bikes, are taller than the stroke of the piston. If this is significant, it might be helpful to measure up from the exhaust port however far your stroke is, and draw a 'top dead center' line. On this vespa, TDC is a full 3 mm below the deck of the cylinder. You can always change the base gasket spacing to adjust the exhaust port to perfectly match the top of the piston at BDC. When you finish up you should have a drawing that looks like this:

From cylinder blueprint
In the case of this vespa, i've marked up the TDC line, the cylinder stud holes which i have to avoid cutting into, and made some notes about deck and stroke.

'The Math'

Now that you know your original port map, you can start to plan the modifications you want. I'm not going to go in depth on this because its a whole different article, or series of articles and there is lots of good info out there already (Jennings, Bell, et al), go to the library, check out a book, and read it.

Once you've calculated your desired port map, take your calipers to the tracing you made and lay out your new 'ideal' port map. You can see on my map where i've laid out the 'horizontal' axis along the bottom, and measured up from the 'BDC' line along the bottom of the exhaust port. In this map, i'm also rotating the porting slightly so i can get more exhaust port in along side that stupid cylinder stud, so you can see where i've laid out a new 'exhaust centerline' and spaced everything off that point. You can also do this all in CAD if you want to take the time to draw it all in cad. Either way you should end up with something like this:

From cylinder blueprint

Now that you've got your port map, take an exacto and cut out the ports. If you're doing 'finger porting' or fully open transfers, you'll want to cut long strips. When its all cut up it will look like this:
From cylinder blueprint

To get the porting traced back into the cylinder now, take your port map, and tape it into the cylinder the same way you did the first time. Alignment again is critical. Align the top edge of the paper with the top of the cylinder, open the tube of paper up tight, and tape it in place. You'll have to either eyeball the centering around the exhaust port, or in my case, the edge of the port near the cylinder stud is going to remain the same so im lining it up with that edge, and level to the bottom edge of the port. Unless you're getting tricky with raising the ports by the base gasket, the bottom edge of the exhaust port is your BDC level. If everything is aligned well and its taped securely in place, the port sizing should work out perfectly.
From cylinder blueprint

Now, we see why we cut the holes out with the exacto. You can either glue the paper in place and use that as your guide, or, simply trace the edges of the paper with a marker. Paint marker is the best, also those 'Pilot gold sparkle' markers work great, because they stick to metal better and are opaque and easy to see with a fine point.

From cylinder blueprint

Now you can pull out the paper and grind away what you've drawn in. The sizes you calculated come out perfectly, and your porting should do what you want.

good luck!

Wednesday, December 16, 2009

What is this doing here?

Maybe its the Wisconsin in me, or the farm boy passed down from my father, but I've always had a soft spot in my heart for the mighty chainsaw. Of all power equipment, it has the most potential to reduce human work, its a two-stroke, and up until retards started buying them at Home Cheapo, they were almost exclusively made in Wisconsin. What more can you ask? Oh you want it to be the most hated entity by hundreds of thousands of smelly hippies and an ideal zombie killing weapon (when attached to your arm). Done.
From Chainsaw

Ok, I admit I have a bit of an addiction to 2 stroke...

Yesterday, Instead of doing something productive relating to homework, getting a job, or the Ciao, I dorked around with this beautiful old chainsaw that was languishing in my buddy's garage. At first i was just going to get it running so i could clean up some brush around my yard, but then he said 'heck if you get it running you can keep it' (I love it when people say that).

So, i tore the whole thing down, cleaned it up, and did a little performance tuning. Once I realized how beautifully this was made, I couldn't resist. A perfect example of 'they dont make 'em like they used to' this thing is entirely aluminum and weighs next to nothing. Its probably 30 or 40 cc's, with a MASSIVE 15mm walboro carb. The intake and exhaust ports are huge, and it has fully open 4-port transfers. It even has some sort of wierd side porting in the piston that looks like its supposed to boost the transfers. It would definitely explain why such a tiny little saw has such a massive blade on it.

From Chainsaw

Talk about some serious slasher-movie shit.

It wasn't running because the points (i cant think of the last time i've worked on lawn equipment with points) were completely out of adjustment. I dont know what they are supposed to be, but I eyeballed it, and put it together enough to start the engine outside of the housing with starter fluid. When it caught it just about tore my arm off... close one. Sure enough started on the first pull.

I ported it with the engine completely together.. because who cares really. After porting the cylinder was hosed out really thoroughly with carb cleaner and compressed air. I went about 1.5 mm higher on the exhaust... width was maxed out at at least 70% of bore. The intake i dropped about 1mm and smoothed out the intake manifold transition. The intake and exhaust were on the sides of the engine, and they were already massive. The stock air filter, as seen under that beautifully styled black grille, was made out of what looked like arts'n'crafts-style felt. I replaced that with a 'hi-flow' chunk of air conditioner filter for a little extra boost (mostly because i was too lazy to clean the old one.)

After putting it all back together, I realized someone had tried to adjust the Wally Walboro carb and failed miserably. The high idle screw was all the way in, the low idle screw was mostly out, and it wouldn't run at all. I put them in the ballpark of 1.5 turns out and got it running on starter fluid, and dialed it in. Holy Crap this thing rips. Definitely one of the scariest chainsaws i've ever used. It doesn't have the smooth balance of say, a Husqvarna, but it revs way higher than it should now, and the inertia of that huge blade just about yanks it out of yer hands. I'm going to dig around for some hockey tape today and try to tape up the handlebars for a bit more grip and to give it that 'freddy krueger' look. Maybe while i'm at it I'll fashion some sort of crude prosthesis for my arm.

Zombie Apocalypse here i come! Does anyone know where i can find a mini circuit pipe for cheap? Maybe one of those Puegeot Faco chambers on treats? How rude would that look hanging off the bottom?

UPDATE:Just got a chance to slice up some brush in the neighbor's yard. Holy damn, this thing is sick. Not quite as fast as my Poulan Pro model back home, but definitely more torque. A smaller blade would probably run faster, but the blade thats on it is really nice with a roller tip and a brand new chain. The autolube isnt working, but i'm sure its just a bad seal or sawdust in the guts.

Update Part 2: I was going to go buy bearings right now, but my stupid landlord parked me in again. Instead I went all Bob the Builder (can we fix it, yes we can! for those of you who don't have 5 year old cousins) on this shit. Turns out I was removing the engine all wrong. When done correctly, you can pull the entire engine out of this thing by removing 6 screws. Yes thats right, the entire engine can be torn down and put back together with a 5/8" socket and a flathead screwdriver. Awesome. Four more screws removed the oil tank, which bolts to the bottom of the engine. This reminded me how much i hate it when people goober RTV all over everything. Someone else had this apart at one point in time, and apparently they felt they knew more about the design of the saw than the engineer who originally designed it (a pretty smart guy apparently, as he figured out how to get the engine in and out with 6 FUCKING SCREWS!) Anyhow, they gobbed RTV all over the mating surface, which happens to go around the passage way that the oil runs through. There was RTV all up in the oil injector hole. Thank god whoever did this was also too dumb to tune a wally carb or else the clutch, roller bar, and chain would probably all have been shot.

In other news, i think the next time i get an extra $25 chillin in my pay pal i'm gonna put one of these on it.

Tiny Puegeot Pipe That looks about the right size for the engine i'm working with. Silencers? Silencers? We dont need no stinkin' silencers.

Friday, December 11, 2009

Black Majik- part 1


From Black Magic motor

One name is enough to say for the early Cranks who knew her as the first truly fast moped in Milwaukee. A faded orange (red?) swinger 2, she had over 7000 miles put on her in the first two years of the Cranks by yours truly. A faultlessly reliable, charismatic, and brash mount, she carried my ass to many rallies, rides, and how-the-hell-did-i-get-home benders. When the countershaft bearings finally went out in the spring of 2008, I shelved her in favor of my newly finished Sachs (Sally) and made great plans for a triumphant return to glory, including disc brakes, magnum x forks, and a case-reed-inducted 50cc powerplant.

Things change, as they always do, and other projects took precedent. The cases got machined for reeds, but the cylinder was never finished, and the decrepit frame gave of itself many small parts as it languished in the fortress. A few months ago I pulled out the original engine with the siezed countershaft, in the intention of hosting a class on E-50 rebuilding. I happened to have an extra 70 TCCD laying around, and decided it was time to finally see what the little piston port could do. The more i thought about it, the more I liked the idea. Annie was never a prissy race bitch with fussy adjustments, picky about fuel, or hard to start. Annie was a creature of the streets, a lean, sinewy, back alley blaster with a heart of cold forged steel. Eager to tear out into the night on missions of ill-intent at a moment's notice.

And so, black majik was born.

When the first build was conceived, 50cc reed inducted, I bought a fully stuffed DMP crank (like, the week they came on the market before people started 'splodin' them) and did some lightening on the countershaft gear. Quite a bit of lightening actually, took about a third of the total mass and about 60% of the rotating mass out of the thing on a lathe.

From Black Magic motor
I got the crank and countershaft ready to go with nice new bearings and seals from my friends at Allied Bearing (they smoke in the office still, awesome dudes) and started looking at the transfer porting.

The TCCD 70 has pretty gnarly transfers stock, but they just weren't good enough for me. The thing that really chapped my balls was there were a couple areas where the ports came way too close to the edges of the case, and vise versa with the case ports, just about sticking out in the other corners of the cylinder. My first thought was to keep it conservative, but then i thought, what the hell, free kit, extra engine... lets get radical.

I made a plexiglass plate that would fit around the skirt and bolt into the four cylinder stud holes. Then I mounted it all down to a 2x6 using wood screws through the stud holes. I mixed up some real nasty pro style epoxy shit and built it up around the transfers. Then i clamped down the plate to leave a smooth finish level with the deck. I repeated the same process for the cases and ended up with this.

From Black Magic motor

Thats after a little bit more porting, not quite finished. A few more hours with a grinder opened up the intake, transfers, and exhaust port. The exhaust was about as big as it could be, the intake got opened up a fair bit.
From Black Magic motor

The piston was modified, but after putting it together i think i went too far. The boost port holes go into the intake port at BDC. I know this will cause it to spit out the carb something fierce, but i'm not sure if it will still run well and be acceptable or if its too far to have any bottom end. We'll see once i get her fired up.
From Black Magic motor

The ignition is installed and ready for a CDI box. Thanks to Matt from Florida, I've gotten a lot of really good advice on my ignition options. What i have here is a early-model A55 ignition coil. It uses a thyristor box like the A35's but it has the smaller diameter with the radial coils like an A55. An ignition with a pickup would be nice because i could run all sorts of fancy CR and YZ 80 ignition boxes with crazy curves and stuff, but this will work for now. It sounds like the A35 box has pretty good curves in it from the factory, so i'll be trying to snag one of those. The mounting simplicity is amazing, just bolt on and go. All the holes lined up perfectly and the flywheel dropped right on in the right place. Awesome. Hopefully the timing works out to be the same, but that is all determined by the box. It sounds like the A35 box will run on this engine no problem, which means the timing is in the same location as a CDI 35 which is the same location as a points 35 which can swap with a puch points stator 100%, so it should all just... uh... work?
From Black Magic motor

In the background you can see the remains of a honda Z motor CDI unit that i bought a few years ago when I was playing around with 12v lights on my Sachs. Its got a good pickup, so if all else fails, i'll mod the shit out of a flywheel cover and mount that damn thing somehow, but it would be way messier than the beautifully stock-looking system i have now. The cool thing about all these 'pickup' type CDI's is they are totally interchangeable with a little hackin'. I'll probably end up putting the XR50 inner rotor on my Tomos eventually.. but thats another post.

Finally buttoned up, all i have left to do is trim that stupid starter gear off so i can get the flywheel cover over it. 80W light power here we come!

From Black Magic motor

Wednesday, November 25, 2009

Santa came early


Thanks to my exceptional good moped karma, I've recently come into the posession of an A55 stator and flywheel. This is the older one without the tabby for the pickup, but if i'm not mistaken, i can get a 2 wire CDI box (some sort of thyristor setup, i'm sure) that will work from an A35 or pre-2007 A55, or i can try to adapt a pickup and get things working with a RM, or YZ80 CDI box... I'm not sure what i'll do yet, but this is a 100-some dollar piece of the high-rpm puzzle that has just magically fallen into my hands and i'm pretty excited. I'll be headed to the machine shop later today hopefully to trim off the stupid starter ring gear, so i can fit it under the stock e-50 magneto cover.

Just goes to show you, never burn your bridges.

Also, lots of new pics up, an article on refreshing a motobecane, and the long-awaited second part of the timing series are in the works... plus a quick and dirty (literally) piece on rebuilding cup and cone style bearings. Ooh exciting!

PS.. if you're as excited as me about this (doubtful) you can scope the first look at my porting pics... pretty gnarly.

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Motobecane L'amour !


Motobecanes are peculiar little creatures. Definitely the most spirited mopeds I've ever worked on. They can vary 10 mph in top speed from day to day depending on how they feel, and go from starting in one kick to frustrating you to the point of tearing your hair out, over night. While it is important, as with any moped, to maintain positive energy and respect the moped's spiritual soverignty, there are a few modifications which, when done correctly, will greatly increase the chance of him/her starting predictably. When done properly, these improvements will not upset your Motobecane, rather will strengthen your bond and make your moby a happier little animal.

To start with, any venture into moby-land is incomplete without a visit to Mabecane's Mobylette page. The virtual proprietor, MaBecane, is one of the most interesting people involved in mopeds. He loves these bikes like children, and shows an unmatched zeal for historical preservation, caretaking, and helping others keep their mobies running long after it makes sense. Check it out here for tons of info and pictures to get you excited about your build: MaBecanerie Also, grab a manual while your at it. The manual is a poor copy/translation, but the verbiage is really pretty, in french style. Lots of adjectives to fully illustrate the tenderness that is inherent to motobecane repair.

Esti (above) is a good friend and former neighbor of mine, she is a perfect candidate for a moped rider, and since riding some bikes when I moved in underneath her, she's been looking for a 'yellow moped.' Not many bikes came in yellow, but i knew of one brand that did, and a Motobecane was a perfect fit for her classy style. I found this 1976 50v in a friend's storage unit, in pretty good shape, completely covered in black greasy grime. The grease protected the paint and chrome, and whoever had it last managed to avoid bodging much besides the carb, seat, controls, and electrical. The cylinder was tight, had good compression, and all the important stuff was there. This is pretty typical of a 'barn' or garage find moped, so I'll go over the common problem areas and detail the repairs and modifications I made to her bike, so a novice could get her feet wet with a reliable and fast machine as she learns the ropes.

Most barn/garage rescued Mobies will have all the cables frozen on them. For some reason the grey cable they used cracks and rusts out like nobody's business. The motobecane uses knarps on everything, though, so you can pick up a full mountain bike cable pack at your local wal-mart, for $7 and cut all your own cables to fit. If you want to get crazy, and replace everything with OE grey cable, you can talk to my friend Matt Quirk, at Motorwest Motorcycles in milwaukee to get a roll of the grey stuff in much higher quality than Motobecane ever intended.

At the very least you'll need new throttle, front brake, rear brake, and possibly decompression. Choke depends on the carb you use.

Speaking of that carb... Motobecanes are notorious for the Gurtner carb. Many moby fanatics will tell you they can go 50 mph on the stock gurtner (i've seen it..). For someone who wants to eat, sleep and breath french, the gurtner is a perfectly workable unit. For most of us however, its much cheaper and easier in the long run to just swap out to a generic Dellorto SHA. You loose the extra cable of the choke, you get standard replaceable jets, air filters, a bigger throttle, and they are less likely to leak with the rubber-tipped float needle. You can use either the real-deal SHA 13 (vespa style), or the Spaco clone (kinetic), or go to a standard 14 SHA or 14 SHA clone (my favorite). The clones might have some issues with changing jets, but if you're hardcore and used to making weird stuff work, you already have a set of JET DRILLS to fix that. In addition to your fuel system woes, the stock petcock is almost invariably broken or leaky. Quarterkick.com seems to have these in stock more often than the other guys, so give Chad Burke a try first. If they aren't on the website, they might still be in stock.

The Motobecane AV7 (50v, 40t, 7, traveler) comes with either a long bendy intake, or a short stubby intake. The stubby intake is actually too small to easily mount a SHA carb (apparently with a little fin grindage the 13SHA fits), but either way, its much easier to just buy the Malossi SHA intake for av7, which is available dirt cheap from the major moped parts sellers.

I've heard some nightmares about Moby Electrical, in fact the first two mopeds I ever owned were mobies left outside for many years, and were hopeless, the coils were all rusted to hell. For most motobecanes in fairly good condition, the coils, condenser, and points are inside the flywheel and fairly well protected. The problem areas with moby electrical are the questionable connectors, namely the white plug thingy under the floor boards, the coil, and the incredibly awful spark plug wire.

The terminals of concern are the white ones under the floorboards. The prongs in them are very small and flimsy and prone to corrosion between the terminals themselves (easy) or between the terminal and the wire (very hard to diagnose) they also have a nasty habit of popping the terminal itself out of the white plastic housing, making it look connected when it isnt. If they look good, hose some dielectric grease in there and forget it. If they are really shot replace them with soldered or properly crimped on blade terminals.

The NOVI coils, white, strapped to the bottom of the tank, are prone to cracking and rusting inside from what i can tell. The spark plug wire is a proprietary unit with compression style terminals, and an obscure 5mm diameter. I would strongly reccomend buying the 'universal moped coil' that the major moped retailers have for sale. It uses a standard 6mm wire with screw post, seems to deliver an incredibly strong spark, and is all zinc plated and epoxy potted for long life. It grounds through the frame so the coil wire should work fine. Everything should be a very simple plug-and-play situation. You'll need two 5mm bolts to bolt it on. dont forget lock washers or nylock nuts. Set the point gap to stock, clean up the points, and you should be getting a nice fatty spark.

For performance stuff, you probably wont need much if you have the 'fast' 30 mph cylinder. They fly pretty well out of the box. Upper 30's with a 14SHA means everything is solid. If not, your timing, bearings, variator belt, or brakes might be at fault, or you have one of the slower cylinders (or your exhaust is plugged, but this doesn't seem to be much of a problem for moby). The only differences between the two is porting. I wont go into it in detail because there is much better info out there, but lowering the intake about 1mm, widening it 1mm on each side, raising the exhaust about 1.5 mm and widening it about .5 mm on each side with a nice radius up to the top, should get you close to the stock fast cylinder specs. It might be easier to take the engine off if you are going through this much work.

Yep yep, so thats about it. Moby refresher in a nutshell. The first time that thing pops to life, you will understand the beautiful feeling. They whirr, they rattle, they glow, they are strange little beasts, but when properly set up they can be amazingly reliable and a real pleasure to ride for many miles. Once you have your bike running and solid, you may also need to replace the rubber engine mounts (which i'll cover in another post sometime) or do some of the other basic tuneup things such as bearings and brakes, which are similar to the Puch demonstrations i'll post up here soon.

Au Revoir!

Sunday, November 22, 2009

Timing Part 1

Timing Part 1- Theory

Ignition timing is a frequently misunderstood and misinformed topic in the moped community. A basic understanding of the physical principles occurring in the combustion process, and the system by which the spark plug motivates this controlled combustion, will allow the tuner to adjust ignition timing to the optimal point in the combustion cycle for maximum power. This article is the first of two parts, detailing the theoretical role of ignition in the power cycle, and the implications various performance modifications have on optimal ignition timing.

To begin, lets look at the role of the spark in the combustion cycle. The ignition event occurs between the compression and power strokes. After fuel and air has been forced into a small volume and raised to a higher pressure, the spark ignites that volatile mixture and the resultant heat and pressure force the piston down to provide motive force (powahhh!!). This at the outset seems like a fairly simple proposition, but in reality there is quite a bit happening in the few milliseconds during which the piston approaches top dead center, and begins its decent.

In reality, considering the spark and combustion of fuel as a finite event (happening all at once), is an oversimplification. The piston is traveling at such a high speed, if you were to slow things down to a comprehensible speed, the movement of the flame itself through the combustible mixture in the cylinder, would seem to happen very slowly. This ‘flame front’ speed is based on the pressure of the mixture of gasses, which is changing as the piston nears top dead center, it is also based on the fuel/air ratio, and the temperature of the gasses in the cylinder.

Going back to the cylinder now, the piston is coming up from bottom dead center, the cylinder is full of air and fuel mixed. As the piston nears the top, the points will close, breaking the flow of current through them, and diverting the electricity to the spark plug. The point at which the points ‘break’ or open, is the point used to determine timing using a timing strobe, a test lamp, or a cigarette paper. There can be a little bit of dwell downstream in the system also, from 1-3 degrees. A hotter plug will spark more readily, also a smaller gap will jump faster, so if you change these, your timing might change incrementally.

When the spark jumps across the electrode gap, the mixture, which by now should be at a very high pressure, will ignite. If the fuel mix is correct, and the piston is still traveling upwards, the flame will burn up the fuel and air mixture in the cylinder just as the piston is passing top dead center (the most powerful combustion will occur when the pressure in the cylinder is highest- e.g. top dead center), and maximum power will be achieved as the pressure from the burning gasses pushes down the piston.

Combustion theory and implications:
Now perhaps it is a bit clearer why ignition timing is so important. If the timing is off by even the slightest fraction of a millimeter, peak power won’t be achieved. This is why many people will say ‘the power is in the points’. In fact there is no power whatsoever ‘in the points’ unless they are set wrong for your particular application. Understanding the various effects modifications can have on the ignition timing, will facilitate better ‘guesstimating’ as to the optimum setting of the points. The key is the relationship between the fuel, exhaust, and temperature conditions and their contribution to flame propagation.

Flame propagation in the cylinder is a relatively simple concept when we go back to thinking of the combustion in super-slow motion. Chemistry tells us that the rate of any chemical reaction is proportionate to the initial energy. In the engine, that energy manifests itself as temperature and pressure. We assume no change in temp. We started with an initial volume of fuel/air mix and compressed it by the compression ratio to get our final pressure. Compression ratio has a huge effect on final pressure, and reaction time- read flame propagation time, but its not the only factor.

The initial amount of fuel/air in the cylinder is called volumetric efficiency, the amount of the cylinder displacement that is filled when the piston closes the exhaust port. A more efficient intake and transfer tract, along with a pipe, or the timing can all change the volumetric efficiency. Anything that increases the VE, will make the flame propagate faster, and will require ignition retard. When a pipe comes ‘on’ the powerband, it is pumping more effectively, and increasing VE. Port timing also can contribute to varying VE at different points in the powerband.

The other major contributor to flame propagation is cylinder bore diameter. For the fuel to all be burned the flame must cross the entire surface of the bore. It might seem small, but going to a larger bore requires more time to burn the fuel.

There is a delicate balance when adding performance parts or modifying your bike. Everything has the potential to change the timing, and we have very little recourse with the simple points magneto system most stock bikes have. The original design is for a relatively constant powerband between 1000-3000 rpm. Wild variations in the efficiency of various parts at various speeds can require dramatically different timings.

Common problems:
Some commonly occurring problems with timing are pretty obvious, but the small, silent loss of power at various speeds that is frequently cited by the ‘power in the points’ crowd, is something that can only be avoided by painstaking tuning. In fact, points magneto systems aren’t nearly accurate or tuneable enough to deliver peak power at all ranges, but usually a happy medium can be found that allows for good performance across a wide powerband.

Should the spark jump too soon, a condition known as detonation occurs. This is frequently referred to as ‘knocking’ or ‘pinging’ and in a highly tuned moped engine sounds a lot like a tin can full of marbles being shook. It is confusing to troubleshoot because of its sibling condition, pre-ignition, which shows up in exactly the same way. Its hard to tell the difference because they both cause the same effect, the noise you are hearing is the fuel/air mixture in the cylinder igniting before the piston reaches the top of its stroke, so the upward movement of the piston is met with a downward explosion.

In detonation conditions, the spark is jumping too soon or the flame is propagating too quickly (same thing, relatively speaking). This is why some bikes with aggressive porting or exhausts require more ignition retard than stock, or some bikes need retarded at higher speeds. As the pipe hits or the ports work more effectively, the amount of air in the cylinder (volumetric efficiency) can increase with a supercharging effect, causing the flame to travel faster throughout the cylinder.

In pre-ignition, the condition is being caused by hot surfaces inside the engine due to the wrong heat range spark plug, high cylinder temps, or too low of octane fuel for the compression. While both conditions result in the same effect, the causes are dramatically different, and the solution is as well. Due to the extreme risk of engine damage these need to be understood and correctly diagnosed.

On the other side of the coin, backfiring and power loss are telltale signs of the timing being too retarded. If the combustion occurs as the piston is already heading back down, it doesn’t take much time at all for the burning gasses to blow right out the exhaust. If this happens, the combustion only acts on the piston for a brief instant, and the piston cant harness the burning fuel. Backfiring can occur in extreme cases where the flames either blow out the exhaust, or even back down into the crankcase when the transfer ports open. Typically in cases where the timing is only very slightly retarded, the bike will have poor or no throttle response, or loose throttle response under load, but maintain it when it is on the kickstand. When there isn’t anything to push, it can rev up, but once load is applied the short amount of time the gasses push on the piston before blowing out the exhaust, isn’t enough to overcome resistance. The transfer ports can even flow backwards or stall depending on the extent of porting or the pipe.

In conclusion..
Timing need not be a mystery, or entirely guess and check. We are just starting to see the types of programmable CDI units that would allow us to dial in perfect timing, but in the meantime, the points magneto systems are perfectly workable, reliable, and offer a very simple, direct type of tuning. Having a good idea going into it about the effects other performance parts can have can facilitate easier tuning, and a better understanding of our bikes.

Thursday, November 19, 2009

Crankcase compression: theory and implications

EDIT: MAY 2014:  
This is an article I wrote 5 years ago, since then I've learned a lot and realized that primary compression is a lot more complicated in its overall effect on an engine.

I don't necessarily agree with all the comments, but I don't really have time (and still probably don't know enough) to properly discuss or refute them. At face value this is a pretty basic article describing the basic crankcase pumping operation on a two stroke. I could take it down, but it helps to remember how far I've come and how much I still have to learn, so I'll leave it, but use it at your own risk.


I originally wrote this for a moped army forum thread located here: http://www.mopedarmy.com/forums/discuss/7/189038/189038/

With the increase of availability of moped parts here in the U.S., we've seen a huge boom in the technical sophistication of domestic tuners. With this availability, everyone seems to be pushing the envelope further, trying to squeeze out every last iota of power from our little machines.

A good example of this is the availability of 'stuffed' cranks. Many of us have purchased them for absurdly cheap through the US moped parts sellers, having only a vague idea of what it really means to 'stuff' a crankcase, why it can produce more power, and what the implications are for the rest of the engine.

Crankcase stuffing is decreasing the volume of the crankcase to improve what is called the 'primary compression ratio'- the compression ratio for the system comprising the bottom of the piston, crankcase, and transfer ports up to the edge of the piston.

Primary compression is defined as Vi/Vf which is:
volume final divided by volume iniitial.
final volume is the displacement volume of the piston plus the volume of the case. initial volume is just the volume of the case.
when doing this for a cylinder, the head volume is relatively small, so we can achieve 11:1 (11/1 = 50cc disp + 5 cc head volume/ 5 cc head vol.) or better. When we do this same thing in the case by either increasing the displacement, or decreasing the crankcase volume (say, by stuffing the crank) we can get better compression ratios...

so what? right? why does changing the compression ratio help us?
having a higher crankcase compression ratio lets us get more air in during the intake phase, and creates higher pressure pushing that air through the transfers.
This is obvious when we go back to high school chemistry and remember PV=T(nr): Pressure times volume equals temperature, if you decrease the volume of an area, the pressure or temperature MUST increase to compensate. In the very short time that the piston is going up and down, we can assume the temp cant change much.
This makes sense for the second part, the transfer pressure. The higher pressure from a smaller final volume will push the air through the transfer ports at a higher velocity, improving scavenging, and transferring more air in the very short time the ports are open. But this only makes sense if we are getting more air in the crankcase in the first place. The displacement of the piston isn't changing, so we cant change how much air gets into the crankcase right? Wrong.

The higher ratio means that when the piston goes up and creates a vaccum in the crankcase, the vaccum is stronger. Even though transfer pressures can be as high as 50 PSI, the intake pressure pushing air through the carb and past your reeds is only 1 bar, because it is being pushed in by the atmosphere. You want to get as close to a perfect vaccuum as possible to get air to transfer as quickly as possible. (This is why piston port engines can blast reeds at the top end, the piston port has much less resistance to flow, but i digress. ) Having a compression ratio of infinity, as in 0 crankcase volume, with no leaks, would create a 'perfect' vaccuum, This would provide 32 PSI across your intake tract from the air filter in. In reality this is impossible, the ratio drops very quickly with increase in volume in the case, and the potential transfer pressure drops from 32 even faster, by PV=T. The time your piston is going up is limited by your RPMs, and the amount of air that can transfer is limited by the pressure, restrictions in the intake, and time. Therefore, if you can make more pressure (by improving the vaccuum in the case) you can get more air in the case on each stroke, which means you get more air into your cylinder, and can burn more fuel.

Tuesday, November 17, 2009

Current Project Teaser

I've got four major performance builds right now that are newsworthy:

Sally Balboa
Sachs 505-2BX- Hand shift, manual clutch, long stroke motor from Roald in the Netherlands
80 cc Athena reedvalve kit
Puegeot 103 pipe by Simonini
Mikuni VM18 carb
More time and custom parts than i want to admit...
From Sachs 2bx-80

Annie 'Black Magik' rebuild- at one time a swinger 2
70 tccd
lots of fancy schmansy custom junk.
From Black Magic motor

From Black Magic motor

Tomos sprinter
70 Alukit, 2 petal polini reed block, 22 mm kehin clone...
custom everything, including beefed up bottom end with roller bearing con-rod, caged bearings, mod. clutches
rigid with dropped front end.
homemade hydroformed pipe
needs to be tuned for E85 and needs some sort of CDI.
From Sprinter

And, last but not least, a project for my buddy Dez, the roadBLASTER
Low budget, old school tuning:
porting, reeds, grindin' up shit.

From Projects

For my pictures

Picasa integrates really well with blogger, through the googles, so i'm using it to host all my pictures. Some stuff will be for sale, some is teaser pics for posts i'll write later, lots of Milwaukee ride photos. Check it out if you're really bored.

From Cranks

The workshop.

June of 2009, My lovely girlfriend Caitlin, and I signed a lease on an adorable cottage/back house. The place was rough, the rent was cheap, but the basement had a 4-Step egress door and a derelict, cluttered workshop. I wish i had some before pictures, because it was a mess; wood everywhere, no light bulbs, dirt floor, trash from the previous tenant all over. The potential was there however, and over the summer of 2009, I've cleaned out the junk, burned the wood scraps, patched up the dirt floor with other scraps, cleaned up the workbenches, and generally improved the heck out of the place.

Fast forward to November, I'm settled in for the long hard winter with a ventilation blower, air compressor and tools, workbenches all around, 'grinding station', lighting, spray booth, and almost every tool i could need to do top shelf moped repair.

I've been rediscovering some long-dormant writing skills, and now that day-to-day repairs are slowing down for winter, I have more time to work on performance tuning, which should be more interesting to write about.

From Cranks

So, I've decided to start blogging as much of this as possible. I've never done a real good job of documenting all my moped projects, but I think its a good idea to make myself work cleaner (as other people will be seeing it) and share ideas with other tuners in the MA online community.

I'm trying to turn writing into a career at some point in my life, technical or otherwise, so please critique the heck out of my posts. I'll do my best to write them in a clear, concise, professional style, and doccument with good pictures.

As you guys correct me technically and verbally, I hope to improve as a writer and engineer, so Thank You for reading! I'd also like to thank Caitlin, my girlfriend for putting up with all of this garbage, noise, and still letting me use her camera and computer to do this. I'd also like to thank the bloggers i've linked, as they all do a great job and motivate me to push harder and work cleaner.

Friday, November 13, 2009


its got that new website smell, hopefully i'll do something with this.