The Ford Barn

rotorwrench · 08-31-2016, 01:01 PM

In aviation we use a differential compression test set. The E2A is the type I've always used. You can see some in this link. http://www.aircraftspruce.com/search...TESTER&x=0&y=0
A person has to get the piston up to TDC on #1 then plug the tester into the spark plug adapter. The regulator, with a shop air hose attached, is then adjusted up the scale of the first indicator to reach 80 PSI. The second indicator will read the differential pressure. If it's 65 psi or better, the cylinder has a good enough leak down to go. If it is lower, a person has to listen at one of the three normal leakage areas, ie exhaust, intake, or crankcase breather. This is how you can tell where the leak is on either valves or cylinder/rings. After you do # 1, you follow firing order for each cylinder till all have been tested

These can be utilized on automotive applications but a person has to fabricate or find a spark plug air adapter suitable to the engine being tested.

To Add for safety, if the engine rotates when you introduce air into the cylinder then you have to stop and turn it back up to TDC opposite the direction it rotated. You can find exact TDC this way if you introduce about 5 PSI while you are turning the crankshaft. Coming up on compression, it will have resistance to turning until it is at TDC and the indicator #1 quits climbing to higher pressures. If you go too far, it has pressure rotating it the opposite direction so a person has to find the sweet spot where it no longer tries to rotate either way. If you put the car in gear and it tries to rotate then you have a problem. Best I can say is DON'T Do That! 80 PSI in a cylinder at TDC can get thing moving better than you might think.

08-31-2016, 01:01 PM	#18
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 18,007	Re: Poor Compression In aviation we use a differential compression test set. The E2A is the type I've always used. You can see some in this link. http://www.aircraftspruce.com/search...TESTER&x=0&y=0 A person has to get the piston up to TDC on #1 then plug the tester into the spark plug adapter. The regulator, with a shop air hose attached, is then adjusted up the scale of the first indicator to reach 80 PSI. The second indicator will read the differential pressure. If it's 65 psi or better, the cylinder has a good enough leak down to go. If it is lower, a person has to listen at one of the three normal leakage areas, ie exhaust, intake, or crankcase breather. This is how you can tell where the leak is on either valves or cylinder/rings. After you do # 1, you follow firing order for each cylinder till all have been tested These can be utilized on automotive applications but a person has to fabricate or find a spark plug air adapter suitable to the engine being tested. To Add for safety, if the engine rotates when you introduce air into the cylinder then you have to stop and turn it back up to TDC opposite the direction it rotated. You can find exact TDC this way if you introduce about 5 PSI while you are turning the crankshaft. Coming up on compression, it will have resistance to turning until it is at TDC and the indicator #1 quits climbing to higher pressures. If you go too far, it has pressure rotating it the opposite direction so a person has to find the sweet spot where it no longer tries to rotate either way. If you put the car in gear and it tries to rotate then you have a problem. Best I can say is DON'T Do That! 80 PSI in a cylinder at TDC can get thing moving better than you might think. Last edited by rotorwrench; 08-31-2016 at 01:21 PM.