Currently rebuilding a friends WR450, and I have a few questions for you YZ experts. Hope it's OK I post here, otherwise please move into the WR page!
Reason for the rebuild was an irritating noise from the upper parts, kind of rattling, following RPM. No loss in performance, no signs of evil in the engine oil. Unknown hours on engine, but I'd guess A LOT!
I've found three things inside the engine upon disassemly that caught my interest:
* Left exhaust valve bucket has some marks on it from the little decompression actuator pin. Light marks on the perimeter of the bucket cam contact surface, no marks in the center of the surface where the cam lobe itself makes contact with the bucket. Normal?
* Massive, and I mean massive wear on the cylinder wall at TDC. I think this is where the noise is coming from, as there would be severe piston slap judging by the wear. Any opinions?
* Some wear in the conrod small end/piston pin. Pin can be wiggled some, feels like the conrod small end bore is slightly elongated in the up/down axis, but OK in the fore/aft axis. Opinions?
Apart from this, the engine seems very nice, never opened before and in great nick.
I am of course replacing the cylinder, piston kit, timing chain, bucket, and crankshaft. Which of these parts are interchangeable with YZ450 parts, and which years are OK in the -06 WR450 engine?
Which aftermarket parts are recommended, and which to avoid?