YZ426F oil pump damage

1 reply to this topic
  • michaeltaz

Posted December 14, 2009 - 02:05 PM


My brother just bought a used 426. I checked the oil pump. Looks like metal pieces went through rotors, according to marks on rotors and sides. How critical are these marks? Must I replace the rotors or cover plate/housing aswell? Can I test the pressure of the oil pump somehow? The oil side water pump seal had blisters on the side where the numbers are. Could this be from overheating? Valve clearances I shimmed. Clutch basket I filed notches out. What else must I check? How can I check timing chain and piston without tearing apart?

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  • grayracer513

Posted December 14, 2009 - 03:23 PM


There are two oil pumps. The rotor set that sits in the cavity in the case is the return, or scavenger, pump, while the one in the cover/shaft/gear assembly is the feed pump.

The return pump does not produce pressure, it delivers volume. The feed pump is expected to produce some pressure, but the amount is not specified, and therefore difficult to test for. Oil that passes through either of these rotors is filtered only by the pick up screen for the return pump, and again by the screen in the feed fitting in the frame for the feed. You should expect "some" battering of the rotor lobes, but how much is too much is kind of a judgment call.

The blisters on the seal, I assume are on the closed, inward facing part of the seal. Those could either be a result of heat (260 degrees is not overheated), or coolant leaking between the shell and the seal coating.

The condition of the rings can be tested via a leak down test. Don't check the timing chain. Replace it.

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