So going about putting my 74 parmakit was actually fairly easy. First of all the stroke is only 0.6 mm off, the motobecane being the longer of the two.
As far as actually getting the cylinder to fit, i first had to bore the cases out. I did this with a sanding drum as opposed to a flap disc simply because I was too lazy to go buy one. I then roughly matched the transfers, just to get an idea if I had to weld extra material. Luckily I did not. Repositioning the studs was also fairly simple. Just thread in studs with jb weld, mark and drill, then tap. Whamo, cylinder fits no problem.
Then there was the difference in wrist pin sizes, this was almost a huge problem, as the jawa wrist pin is very big compared to the moby. After a bit of measuring, I realized something amazing; if you press out the jawa bushing on the con rod, the mobys stock needle bearing fits like a glove!
So the only other variable now is the con rod length. I have yet to order bearings and seals, but Brian and I were out in the garage one night drinking and talking and measuring, and we figured out that the difference in con rod length is almost completely made up for in the difference in case deck height! That is to say, jawa has a shorter con rod, but lower deck height. It was meant to be.
I know some people have voiced their concerns for the vertical engine style fins being an overheating issue, but in my tribute to my first true engine love, i will be throwing a v1 fan and shroud on this thing.
Whew that was alot of words, so anyways, long story short, cylinder is on and it looks like it’ll work. I am still undecided about carb and pipe, but its definitely gonna be some big boy parts.