yz400 Frankenstein Help asap

I have a 98 yz400 that i got for free. Yes, free. The only thing good about this story. Anyways...

So long story short, I tore the bike down completely to rebuild from frame up. Motor was ran for a while with a blown head gasket. So the top end is apart, I had heard rumors that I could run a 450 piston in this thing inside a 426 jug. I have a boat load of parts for this bike, literally 99% of what i need to have this thing brand new.

I just need your help with the last 1%. I have a new top end for a yz400, have a top end rebuild for a 450, and I have a new jug for a 400 plus another for a 426. What are my best options??

I had to have the surfaces decked on the stock clylinder beacause of the damage from the blown gasket. I was told im going to need to run two head gaskets now to compensate.

So basically if anyone could give me advise or input on this process/ anyone done this before?

P.S- Im having trouble getting my hands on new copper washer/ ring things for the oil lines can anyone help me find these?

What is the condition of your crank? If it questionable, I would rebuild it with a 426 rod and use the 426 cylinder, gaskets, piston and pin with the 400 head.

Or it sounds like you can use the 426 cylinder and 450 piston on the 98 small pin rod.....if you think your bottom end is up to snuff.


90430-10188-00 GASKET

90430-08119-00 GASKET

Edited by moto2000

:thumbsup: thanks a bunch

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