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2003 400ex knocking

4778 Views 4 Replies 3 Participants Last post by  tabletop
I took on a project in which this quad ran low on oil and was driven for a short while after. Supposedly, the engine burned oil and the low oil level was not noticed until the knocking sound began. It sounded like a knocking rather than a rocker arm clatter. I pulled the head and jug off to find the back(intake side) of the piston was scored from top to bottom. The cam/rocker/valve ass'y, rings, cylinder, wrist pin, connecting rod all looked good yet. There is a blue discoloration on the crank counterweights where the rod pin is. I'm not sure if that's from the factory, or because it ran low on oil and overheated. The crank and rod do not bind anywhere and do not seem sloppy. I'm wondering if the knock could have been from piston slap? I'm also not sure how to tell if the timing chain and tensioner is worn out. There was tension on the chain when I took the tensioner out. Can I get away with just installing a new piston kit and honing the cylinder? Thanks
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I agree with Shadetree, but make sure you check that rod bearing by grabbing the rod and trying to move it up and down. A little side to side movement is normal, but if it has any up and down movement where it attaches to the crank, the rod bearing is bad.
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