00' wr400 cylinder damage

Has anyone rebuilt the top-end and gone to a larger displacement?

The piston and cylinder are scored about an inch wide, due to rings melting. The only other noticeable issue is a bit of bluing on the cranks, right next to the rod. Is it possible to rebuild with a 426 piston,cyliner and rod? All of this could have been avoided with an ignition cover guard! I'm sure happy that Yamaha waited until 01' to figure that out. Thanks for any help,tim

The bluing on the crank is normal to a certain extent. You can have your cylinder bored to 2mm over that will put it to a 416cc displacement (known as the 420 kit). Cometic makes the oversized gasket kits.


what oil were you running, when was it last changed, how did you realize the cylinder was scorded, and finally, good luck with the fixes.

the wrooster

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