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


  1. Nice work Graham. The porting looks nice and smooth.

    That piston is shot tho. I did the same thing to my TCCD piston, had pretty normal low-end but it didn't want to go past 40MPH with a lot of stutter and fuel spraying everywhere. Fixed it with a new K-star piston.

    I'm curious how that secondary gear will hold up. Most people that lighten that gear end up picking pieces of gear out of their trannycase after a while.

    I like your ignition ideas. Can you get back to me on that if you get a CDI to work with the engine?


  2. Holy SHIT man. That cylinder is amazing. GREAT work, especially with those transfers. Inspiring.

  3. even with that starter gear gone, will that flywheel fit under the puch cover? that looks about 1.5 times thicker than a stock puch flywheel.

    looks great so far!

  4. i was thinking i was going to do the same kind of thing to the secondary gear in my polini class bike! it's awesome to see that someone has done it before! plus i feel like this method would result in a stronger gear than cutting out every other spoke like most kids do.