gas engine compression check

[67hat34c]

I am going on saturday to run as many tests as possible. I remember reading on this forum about compression test and second test with adding teaspoon of oil to the cyl. can someone describe this , i believe this test was to diagnose rings.

 

[Norm Mayer]

That is correct. Add a teaspoon of oil to the cylinder, thru the spark plug hole, then retest the compression. If the compression improves significantly, it indicates the compression loss is past the rings. Beware, don't use any more than a teaspoon. A slight increase can be expected even if the rings are fine, so don't jump to conclusions. Good luck!

 

[Maynard Rupp]

here is a good guide line. Both of our Crusaders have between 145 and 150 psi in each of the 16 cylinders on a compression check using 4 full compressions on the cylinder being tested. I don't believe in adding oil for any test. If you have a low cylinder, build yourself an air lock. You can beat the inards out of an old plug and weld an air fitting on it. Now bring the piston to top dead center on the compression stroke,(hold your finger over the air lock fitting and let the compression blow your finger off). Now clip on your air hose with 80 psi regulated air. If you hear leaking, (throttle should aleays be full open for any compression test), listen by the carb., then remove an oil filler plug and listen there. If you don't hear any hissing, climb on your swim platform and listen by the exhaust. One of the three will be hissing and telling you whether the problem is rings, intake valve, or exhaust valve.

 

[tim45haley]

Worst case senario.....hearing hissing up through the cooling system.....bad head gasket, cracked head/block??? ugghhhh

tim

 

[Maynard Rupp]

Worst case senario.....hearing hissing up through the cooling system.....bad head gasket, cracked head/block??? ugghhhh

tim

If the head gasket is blown between cylinders, which is quite common, you will have 2 cylinders next to each other that check at near zero. To verify, put a sparkplug in one of them and re-check the other ones compression. If it comes up, you are sure the head gasket is leaking between those 2 cylinders.