'01 YZ426 burns oil like a 2 stroke
Posted May 28, 2015 - 04:15 PM
What should I be looking at? Never worked on a YZ before but I have 2 CRF450R's that I've gotten pretty intimate with...
Posted May 29, 2015 - 12:30 PM
You're certain it was oil, and not coolant you saw "smoking"?
Posted May 31, 2015 - 09:31 AM
May be worth the time to pull the exhaust and inspect and clean the header, mid pipe and can for accumulated gunk. If it was timed 4 teeth off, who knows what else may be inside and it may just be remnants of the previous owner. Start with a clean and fresh exhaust, along with clean and properly working upper end, jug etc. It may be the only way to determine what is going on.
Posted May 31, 2015 - 09:44 AM
Have a new hi comp weisco piston on the way. I have decarbed the head and exhaust, so we will see how she runs with the new piston.
Posted May 31, 2015 - 06:56 PM
The piston is not supposed to be round
It expands when hot
Posted June 01, 2015 - 06:56 AM
The shape of the piston has nothing to do with thermal expansion, but it's true that the piston is not supposed to be cylindrical in shape. The only place on the sides of the piston that it should be truly round is the ring lands, the area above the skirt. But there isn't intended to be any wear or contact in that area, so it doesn't matter, really. If the piston were full skirted, like a 2T piston, then its proper shape would be that of a barrel with the sides pushed in at the wrist pin bores so it looks oval shaped from the top, and barrel shaped from the side.
The reason for the shape is to reduce friction and also to manage piston thrust against the bore, especially during the reversals of direction that occur at the top and bottom of the stroke.