Cylinder head/valve testing
Posted: Fri Dec 22, 2017 12:30 pmI know some of you have had valve problems as have I. And, you may have ended up with a spare cylinder head. I had a leaky exhaust valve on #1 and elected to try polishing myself. The compression test was down to 80/40. I had another head from a problem with a broken oil ring earlier. So I replaced the head with a good one and proceeded to polish the bad valve. I removed the valve spring and chucked my drill on the end of the stem. With valve grinding compound in the seat I pulled and rotated the valve both ways. I could see the contact area that was gradually going all the way around. The valve appeared to be slightly off center in the seat. Only a few thousandths and it polished out rather quickly.
I know others have tested valve sealing by pouring a liquid into the head and looking for leaks. I wanted to do the standard compression test instead. I cut a wood plug from a piece of one inch oak that fits the cylinder bore and put a thin layer of gasket material on the edge where it contacts the head face. Placed face down on a plastic bag on a flat surface makes a nice gasket. You can do this with or without the fire ring. A piece of steel plate drilled for four hardware bolts holds it in the bore. Don't go lightly here, 80 psi on a four inch diameter is a load. The compression test came out 80/72. Theoretically it should be 80/80 but testing with soapy water showed a small leak around the wood plug. But now I have a spare head with a known value and I didn't have to put it on the engine to test it.
I know others have tested valve sealing by pouring a liquid into the head and looking for leaks. I wanted to do the standard compression test instead. I cut a wood plug from a piece of one inch oak that fits the cylinder bore and put a thin layer of gasket material on the edge where it contacts the head face. Placed face down on a plastic bag on a flat surface makes a nice gasket. You can do this with or without the fire ring. A piece of steel plate drilled for four hardware bolts holds it in the bore. Don't go lightly here, 80 psi on a four inch diameter is a load. The compression test came out 80/72. Theoretically it should be 80/80 but testing with soapy water showed a small leak around the wood plug. But now I have a spare head with a known value and I didn't have to put it on the engine to test it.