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Discussion Starter #1
Anyone who has ever rebuilt a motor has ran into the fact that most gasket kits include extras. Specially base gaskets.

So I'm working on this motor and the gasket set that came with it has 4 base gaskets. 3 of them are green and are thinner than the 4th, a black one.

Looking online, I'm seeing other gasket sets for the same cc motor either have 3 greens and no black, or 3 greens and a black.

Now, the motor I'm working on has been rebuilt before. I've been replacing every gasket and seal on a complete rebuild of this motor and was curious of how you determine which gasket(s) to use in this case. When I pulled the motor apart, it had a single green base gasket, so my thought is to use the same green base gasket.

I've heard that the reason they include more than one is to be able to shim the motor, but how do you determine if it needs shimming at all? I've never seen a motor with more than one base gasket. I've worked on probably a dozen different motors.

This motor happens to be a Skidoo 670 HO, which has a higher compression than non-HO. The gasket set for the non-HO does not come with the black gasket, which makes me wonder if I should use the black one for this as the previous rebuilder may have made a mistake.

The failure in this case was a burned up PTO piston. Like it ran lean or had a lot of pre-ignition going on (possible, because it requires 91 octane and if the previous owner put 87, it could cause this least I'm told that.)

I've not really been able to find the actual cause of the problem. PTO seal looked fine, but it did leak some oil when I poured some oil into the crankcase, which makes me thing it wasn't fine and was leaking air. I replaced the seal of course, but looking at the old seal, there are no signs of breakdown. Usually you get a spot covered with extra goo or something, but nothing, it looked brand new.
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