Expert: Bill Silver - 11/7/2009

Question
Hello there, I am putting a 1985 vt500c motor back together after the pistons, and rings were replaced. I can get the pistons back to TDC from checking the timing marks. But how do i know what stroke the piston is on and if i have the cams correct at timing? This maybe way simplar then what im thinking. I have to front piston and cylinder put back together, except for checking timing, and the rear is still all apart. There wasnt any notes taking so im not sure what stroke the piston is on. Worried that when i get motor back in bike, ill have timing all wrong just to have to take out motor again. Thanks for the time, Chris.

Answer
Chris, the crankshaft doesn't really know what stroke it is on. The piston is either up or down or somewhere in between. What constitutes one of the 4 cycles is how the cam timing is affecting the valve train.

When the piston is at TDC, the valves are either both closed on compression stroke or both slightly open at the overlap phase (end of exhaust stroke, beginning of intake stroke). Generally, when you are installing camshafts, the valves will be closed on compression stroke, with both cam lobes pointing down towards the piston crown.

With piston at TDC, install the camshaft and observe the markings on the sprocket, to ensure that the camshaft timing is correct and in synch with the piston movement.

Bill Silver