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2003 400ex knocking

4765 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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Thanks, I'll be sure to measure the cylinder.
The rod seems to have no slop up and down. I wonder if the knock was from piston slap? I'm leaning towards just honing it out and installing a new piston kit, and callin her good.
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