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rockieman

Big Bore Kits

4 posts in this topic

I'm looking at going to a bigger bore for my '99 400 rebuild. The original cylinder appears to be in pretty good shape, the bike has roughly 8500 miles which leads me to believe "it's due".

Anyone have any personal experience with the following?

http://www.maxpower-engines.com/big-bore-kits/yz417f.htm

http://www.rageperformance.com/big_bore_kits.htm

http://kustom-kraft.com/YAMAHAKITS.html

Others I should consider?

Thanks in advance for your input. :applause:

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I have the Max-Power 490 kit in mine. Very happy with it. Max Power is first class but expensive. I had the engine completely rebuilt last winter and put about 4,000. miles on it since then. Still purrs! :applause:

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if i were you, ( i have considered doing this myself) i would upgrade to a 426 cylinder drops right on. and a 426 piston AND rod. boring a 400 bigger has been known to cause premature rod failure. the 426 rods at the piston end were bigger to increase strength. then if you want in the future you could overbore the 426 cylinder to 444cc. or go to powroll for a stroker!

if you get OEM parts from the thumpertalk store, it will work out at a decent price.

i think from memory you would need

426 jug

426 piston

426 rod

426 head gasket and base?

cheers - Brett

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