Piston to Valve Clearance

[Mad Mart]

The engine I'm rebuilding has a high-lift cam installed. The engine was running ok the last time it was on the road but I noticed some small dings in the piston crowns when I stripped it. I would like to check the piston to valve clearance to be sure all is ok.

I know there are a couple of ways to measure this, one using clay, plasticine, putty or similar. I don't want to do it this way as it doesn't seem very accurate. I'd like to measure the valve lift with a dial gauge at TDC then measure again at the appropriate BTDC & ATDC. At what point (angle of the crankshaft) should I measure the inlet & exhaust valves either before or after TDC?

[tony g]

15 before and 15 after should be enough. If you are using light springs for checking you can also rotate the engine and press with your thumb to open the valve(s) to feel when they get close. Cam timing will obviously affect the clearances relative to btdc and atdc too

Tony

[Mad Mart]

Thanks Tony. I thought it was something like that. Yes, I propose to use some light springs so I can just press the valves down.

[dursley92]

Don't forget with the engine running and everything hot, especially at higher revs, the pistons will come up a couple of thou higher in the bore.

[Mad Mart]

Thanks Russ.

What would you guys recommend as a minimum clearance?

[dursley92]

Thanks Russ.

What would you guys recommend as a minimum clearance?

Good question! Sorry I am not the best one to ask, I was just pointing out that what you measure on a cold dry engine will not stay the same when its running.