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2000 XR250R - which TDC point to check valve clearances on?

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On my 2000 Honda XR250R. When I turn the engine over using a socket and ratchet on the left side flywheel to crank nut, there are two distinctly different in 'feel' TDC points.

The first, when I line up the 'T' mark with the index notch, the mark will stay lined up. At present my valve clearances are far too tight at this point.

If I rotate another 360*, and again line up the 'T' mark with the index notch, I actually have to continue to hold the ratchet there for it to remain in place. If I let go, the flywheel will rotate itself to a point that is approximately between the 'T' and 'F' mark. My valve clearances are currently correct at this point.

Any ideas which of the two I should be setting my valve clearances on? Why does it rotate itself on the one - does it have to do with the camshafts position?

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The one where the valve are tight is the exhaust stroke and the valves are both opening/closing at that time. Check clearance on the compression stroke only. It does not have to be exactly on TDC, just fairly close, both valves are on the base circle of the cam on either side of TDC.

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Watch the rocker arms as you rotate the engine in the normal running direction. When the intakes start to close, the piston is coming up on the compression stroke. Continue to rotate the engine until the "T" mark is lined up, you can then adjust the rocker clearance. As you noticed, the crank does not want to remain stationary when you line up the T mark. Use a ratchet and socket on the flywheel nut and brace the ratchet handle against the footpeg to hold the crank. Also, before adjusting, check the RH exhaust rocker for having no clearance...this means the auto decompressor is engaged...if that is the case, you will need to slowly rotate the engine around again to get the autodecomp to release...this might take more than one cycle.

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