Piston To Valve Clearance??

[ronzara]

Whats the best way to find this out??
Is it all math or is there a physical way to find the answer?
RZ

[hound dog]

RZ,
One of the oldest ways is to add some modeling clay to the top of the piston, install the head and rocker arms and rotate the engine two turns, remove the head and section the clay to see how much clearance you have. Another easier way is to install the head with a weak spring such as a brake spring on the two valves, rotate the engine to top dead center and put a dial indicator on top of the valve. Push the valve down until it touches the piston and note the amount of travel. Subtract the amount of cam lift at the valve from this measurement and you have your clearance. Easiest and gives the truest reading.
h dog

[speed220mph]

Taking the weak-spring method another step, make sure you install a head gasket, then two lifters, pushrods and rockers for the intake and exhaust set to zero lash. The crank needs to be at TDC on the compression stroke when doing this. Don't forget you also need the cam and timing set installed, too. It would be helpful to have a degree wheel set to a known TDC for #1 rather than using divisions on the crank damper.

Rotate the crankshaft clockwise and bring it up toward TDC on the exhaust stroke. When the crank is about 15 degrees BTDC, push down on each valve until it contacts the piston. This will be piston-to-valve clearance at that position. Measure and record valve movement. Do this for each degree until the crank is 15 degrees ATDC, recording each clearance as you go. This will tell you exactly what piston-to-valve clearance is in the TDC neighborhood.

One thing this won't tell you is the position the valve is in relation to the piston, which is something you'll need to know if you're
installing larger valves with pistons flycut for smaller valves. That's another story.

[Mr.Fixit]

Just do the lump of clay method and rotate the crank twice, it is nearly foolproof. Pay attention to the amount of resistance, if it gets "tight" rotate crank backwards and check clay, the valve might allready be touching the piston top.