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