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Discussion Starter #1 (Edited)
Have acquired another 500T, running well but very hard to start, the starter could barely turn it over and with the kick starter it was equally hard to turn. As said runs well once started no obvious noises.
Removed the plugs and it spins freely both kick and starter motor. The obvious solution is high comp pistons or shaved head. Pulled the head off and removed the pistons they appear to be standard, very little carbon, no sign of the pistons touching the head or valves.
I have compared the pistons with another 500T set no difference, (the pistons are 70mm bore and numbered 375-2) the head is standard and has not been shaved the cylinders are also standard as are the head and cylinder base gaskets.The engine is low mileage 12000 on the clock, and from the ware about right. But the motor has been apart before.
I am stumped!
Didn't check the valve timing before pulling the motor, but fail to see how that could be the cause?
Does anyone have any ideas?

PS. have another running 500T to compare with and that does not have this problem.
 

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Put it back together, adjust the valves, and do a compression test, preferably after running it long enough to get up to operating temperature.
 

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Discussion Starter #3
Sorry J-T I don't understand your post. Are you saying that the valve timing could be the cause of there problem? The only way I can think of that would make cranking difficult, is if one cylinder was compressing and the other drawing a vacuum, but is that possible?
 

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If the inlet cam was advanced,from the stock spec, compression numbers would be higher. Advancing the cam closes the intake valve sooner. At cranking speed less air will be pushed back through intake as the piston rises from bottom dead center, more volume of air compressed equals more compression.
 
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Discussion Starter #5
Thanks Mike,
I understand you are talking about "air column inertia" I would not have thought it would make that much difference.
However since the cylinders, pistons and head and not the problem it must be in the valve train. Nothing for it but, as T-J advised, to assemble the engine making extra sure of the correct valve timing, not always easy with Mr Honda's pathetic cam timing marks.
 

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Discussion Starter #6
Have the motor back in the bike after a valve and seat grind, the problem is gone and the motor starts and runs well.
There was no problem with the head and piston clearances so it must have been the valve timing. Made absolutely sure I had it correct before I put the motor back.
Would have loved knowing how much and which way the valve timing was out but too late for that.
IT WORKS and that is the main thing.:p
 

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Thanks Mike,
I understand you are talking about "air column inertia" I would not have thought it would make that much difference.
However since the cylinders, pistons and head and not the problem it must be in the valve train. Nothing for it but, as T-J advised, to assemble the engine making extra sure of the correct valve timing, not always easy with Mr Honda's pathetic cam timing marks.
Glad you have it sorted and running well. You should take the opportunity now to re-mark the cams with something to improve the visibility of the timing marks, like MegaCycle did on this set I have

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