how do you check valve clerance on pistons?

Answer 1

On an engine that is together or apart? Also what configuration ohc/ohv? . It also depends of the grind of the cam (lift and duration). if the engine is together. I've ran into cases where I had valve clearance for pistons on power stroke--but not on the cylinder at valve over lap, because cam profile was too fast (high lift and long duration). this is a case where there is about 16 different ways of doing it based on different engines-- different head gasket thickness and compression of the same gasket. valve types and thickness. valve seats, pop-up pistons, hemi pistons, blower and turbo charged, solid lifter or hydraulic-----to much information needed to tell you. Leave this to a professional. it is much cheaper to pay me as a mechanic to make a mistake and I have to fix it--- then you to have to pay for your own mistake.
There is no point telling you one way-- when all you could have used is a dial indicator and a pry bar. Take the cylinders (one cylinder per side on a "V" formation--just to be sure) to tdc on both strokes. put the dial indicator on the top of the rocker above the valve stem, depress the valve by rocking the rocker and record the messurement on the dial indicator. similar for an overhead cam--but a little different. Then if you have more than 0.030 movement, you will have more than enough gap. Several engines like the cummins 5.9 B-series diesel will have around 0.020--less then thickness of the head gasket (piston will rise above the deck, and valves protrude above the head deck. The clay methode is only used to check the size of the combustion area. and will deform into a mess if the valves depress into the clay as the engine is turned.-- one valve at a time at most parts of the strokes. That and clay will not conpress easy---may not only do damage trying to get a imprint, but end up having clay in the piston ring area, in the valve port area (that may break free later while running) and going threw head gasket sets (once torqued--you never reuse a head gasket) and large amounts of time building and rebuilding the upper end of an engine--let a lone taking the pistons back out to remove clay in the ring areas------ must be advise from some one that once read a magazine on combustion sizing and has never checked and tried his advise in real life.

Answer 2

There are no valves on pistons. To check valve clearance - most vehicles have non-adjustable hydraulic valves, btw, - remove the valve cover, and use feeler gauge when for each valve separately when the camshaft is in specific position.

Answer 3

Install crankshaft and pistons. Degree camshaft so it is installed/phased correctly. Install 1/4"-1/2" of modeling clay on top of piston you want to check. Spray Pam or cooking spray on head combustion dhamber, so clay won't stick. Install head with head gasket and a few head bolts. Install 2 solid lifters on cam lobes of cyl you want to check. Install pushrods, rockers, etc. Set valves for zero lash on base circle of cam. Roll engine 2 revolutions. Remove head and examine impressions in clay. Maybe section clay at thinnest point, and measure thickness. For a Pontiac V8, you want about .100" clearance to prevent P to V contact. Check at least one cylinder on each side of engine.

Be sure to check valvetrain geometry and valvespring running clearances as well, using same procedure.