i'm hoping the crank to input shaft centres are the same.

if that's the case i'll just slot the crankcases to fit the larger primary clutch gear and machine a sort of oblong top hat to weld back onto the top crankcase.


the short motor i've bought hasn't got a clutch, so I'll just have to keep my eye out.

might nip down dk this week and see if they've got anything in the engine room.

might be worth giving the guys at cross customs a bell, they stroke the crank on their 500 drag motor.

I'm very interested to see how this will turn out

Check my project thread for further updates.

So I believe the 442 kit I have uses Yamaha FZR600 pistons. Having fitted them and checked the clearance the ends of the central ridge are contacting the head. I'm not sure what machining is required? Whether taking a slice off the top of the piston is enough or if more intricate work is required. Has anybody done this before that could shed some light on the matter

if you wait a few weeks i'll be able to tell you the answer.

That would be great, I really want to get the bike running. I haven't changed anything else on the engine except the bores and pistons. I don't know much about the kit as i've received it third hand but unused and I'm not sure if the pistons have had any machining already carried out or not.

What was the end results?

so its been a while, but here's where i am.


gk73a primary gear on the left and my new gk75 gear on the right.



this gear allows me to use a gk71b crank in a set of gk73a cases, with a gk73a clutch basket.

fitted to the gk71b crank will be a set of gk73a rods with fzr400 (3HE) pistons.

this should give me 494cc

there is still an amount of work to do, in terms of the fact that the crank sticks out the left hand side of the engine too far and theres no where to bolt the generator on to, but those are little issues.

Hey Chris I have the answer!
Stick the motor in my 71b frame, stuff the Genny and 1/4 mile the mother.