Checking valve to piston clearance.

[EVIL]

I have my short block and heads ready to be put together and would like to check the valve to piston clearance.

I saw a video on line where the person used clay on the piston, put on the head gasket and tightened only one of the center screws.

Now, what is the minimum clearance needed and with the head gasket be compromised in any way after performing this test?

thank you

D

 

[NCTURBOS]

I have my short block and heads ready to be put together and would like to check the valve to piston clearance.

I saw a video on line where the person used clay on the piston, put on the head gasket and tightened only one of the center screws.

Now, what is the minimum clearance needed and with the head gasket be compromised in any way after performing this test?

thank you

D

There's a couple ways to do it. If the cam is not installed you'll need your cam card to know what the TDC lift #'s are.


K.

 

[Nick Micale]

Do NOT use a regular valve spring, it could cause damage if the valve hits the piston.

Use a spring heavy enough to depress the clay, but soft enough not to bend the valve in the worst case.

Head gasket will be fine.

 

[turbofabricator]

Use a solid lifter to check piston to valve clearance.
Put dabs of modeling clay on the piston, spray the valves with WD-40 (so they don't stick to clay) then turn the engine over SLOWLY with the cam installed properly degreed. If it starts to hang up, STOP, pull the head and check for valve to piston issues before pulling harder on the turning bar/wrench. It is best to do this with the rings off the piston, too, to help reduce rolling friction. Or, turn the engine to 10* AFTDC and then compress the light springs (or set-up springs as they're known) with a screwdriver/pry bar carefully with a dial indicator on the valve stems and measure the distance it moves before touching (lightly) the piston. If you used the clay method, remove the head and cut the clay in half and measure the thickness at the thinest area to measure the actual piston to valve clearance.

 

[TD2593]

Make sure you also check the radial clearance as well. I personally will not run P/V closer than .090" you can move the cam around a degree or two that too will change the P/V clearance. The clay method works great and is easy to do.

 

[mikestertwo]

I check it without using a head gasket. If your good without a head gasket your definitely good with one.

 

[EVIL]

Thanks for all the advice.

What is radial clearance and how do i check it?

D

 

[TD2593]

Thanks for all the advice.

What is radial clearance and how do i check it?

D

The radial clearance is the clearance the valve has around the edge of the valve as it goes into the valve relief in the piston. You can use the clay for that as well.

 

[novaderrik]

Do NOT use a regular valve spring, it could cause damage if the valve hits the piston.

Use a spring heavy enough to depress the clay, but soft enough not to bend the valve in the worst case.

Head gasket will be fine.

other than making it a little harder to turn the engine over, how could a regular valve spring cause any sort of damage if the valve hits the piston? i believe that it's pulling the valve away from the piston..

 

[turbofabricator]

other than making it a little harder to turn the engine over, how could a regular valve spring cause any sort of damage if the valve hits the piston? i believe that it's pulling the valve away from the piston..

Because its hard to tell at what point the valve touches the piston. Using set up springs, (ball-point pen springs. Not really, but they are REAL light. Only enough tension to hold the valve shut.) it is real easy to "feel" the moment the valve touches the piston. Also best to do this operation with no rings on the piston, too. The less drag there is on the rotating assembly, the easier it is to feel contact. Oh, ya, leave the rear main seal out, too. I usually install just one rod and piston assembly when verifying piston to valve clearance.

 

[SS/GN]

Or, turn the engine to 10* AFTDC and then compress the light springs (or set-up springs as they're known) with a screwdriver/pry bar carefully with a dial indicator on the valve stems and measure the distance it moves before touching (lightly) the piston.

I think this is the best method today,I usually do 10 before and 10 after :biggrin:

Kevin