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Discussion Starter · #1 ·
Hello,

I recently stripped and re-built the top end from my 1990 TRX 300 Big Red. I replaced piston rings, head gasket, valve stem seals, lapped in valves etc etc. I timed the engine in conjunction with the Haynes manual. When I restarted the engine after re-build it was missing badly and very lumpy on low throttle/idle but seemed to pick up and rev fine on full throttle. I re-checked the timing and noticed the lines on the cam sprocket don't line up exactly with the cylinder head face - possibly half a tooth out or less. After several attempts of adjusting the timing I still can't get them to line up exactly.
Is it known for the cam chains to stretch on these engines? The engine was running perfect before I stripped it and I can't see how the chain could have stretched? I have since removed the carb and currently in the process of overhauling that just incase it's a fuelling issue. If that doesn't cure it then I'm stuck? The valve clearances are spot on, plug gap fine - basically all the routine checks are good! The only issue I have is the cam sprocket lines not lining up exactly straight when the crank is at 'T' mark.

Any suggestions would be very much appreciated!

Thanks,

Bruce
 

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Discussion Starter · #3 ·
I purchased the complete gasket set from a company called 'Wemoto'. The gaskets were a direct replacement. They were not genuine Honda parts but seemed good quality.
 

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Forget the gasket as the culprit. The cam chain is worn and the timing marks are not perfect. The natural wear of the cam chain is taken up by the tensioner. As the chain wears the front timing mark will be above the surface and the back mark will be below the head. Set it this way and it should run like it did before you rebuilt it. For correct timing, install a new cam chain or slot the cam sprocket bolt holes so the cam can be degreed according to specifications.
 

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Discussion Starter · #5 ·
Thanks very much. I think I've got the timing spot on so I will try the carb once its been rebuilt and go from there.

Thanks to everyone for their help!

Regards,

Bruce
 
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