2003 400ex knocking

4777 Views 4 Replies 3 Participants Last post by tabletop, Oct 19, 2010

tabletop

Discussion Starter · Oct 19, 2010

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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shadetree

· #2 · Oct 19, 2010

tabletop said:
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

as for the blue color on the connectiing rod..this is normal..if your cylinder isn't out of round ( tappered in it )..and your cam/rockers/timming chain/valves are ok..then you can get by with just another piston and rings. before you go out and buy all this..first have your cylinder mic'd..and see how bad it is ???.if it's not out of spec..then go for it. get another piston..rings..top end gasket kit..slap it back together..it should be fine. as for your timming chain tensioner..inspect your chain..timming chain guides..are they worn ?..broken ?..is the chain streched to bad ?..if not..reuse it.

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