Compression test results and questions

[Carlosl151]

Hey guys, I have a 92 12v cummins. I just did a compression test and the results were this in each cylinder
1- 350 psi
2- 350 psi
3- 320 psi
4- 350 psi
5- 350 psi
6- 330 psi

Are these numbers healthy or am I on my way to a rebuild? Thanks

[TheHammer]

Do a cylinder leak down test on 3&6. During the compression test, did the gauge jump to 320 or progressively climb?

[Carlosl151]

Originally Posted by TheHammer

Do a cylinder leak down test on 3&6. During the compression test, did the gauge jump to 320 or progressively climb?

I cranked all of them for 10 seconds. Some went up to 350 after the 10 seconds. Some went up to 325 or 300 and I wanted a couple minutes and cranked again for 3 seconds and the ones that were at 325 rose to 350. #3 went from 300 to 320 after the second crank

[kawi600]

Leakdown test will give you more info like cross-leaks on the head gasket, etc.
you can get the testers cheap. I got one for doing 2stroke engines (I like the mityvac better for this) but I think you can use on diesel if you can get creative with some old injectors or buy the proper fitting.

I have ~360psi cold in my 12v with stock pistons, hamilton 181/210 cam.

[TheHammer]

Originally Posted by kawi600

Leakdown test will give you more info like cross-leaks on the head gasket, etc.
you can get the testers cheap. I got one for doing 2stroke engines (I like the mityvac better for this) but I think you can use on diesel if you can get creative with some old injectors or buy the proper fitting.

I have ~360psi cold in my 12v with stock pistons, hamilton 181/210 cam.

If he has the tool simulating an injector, he is already equipped, just needs a gauge block w/gauges. You need to verify if that pressure is going between the valves/seats, out a crack in the head between the injector and valve seats, potential gasket issue or solely into the crank case.

I know you have 2 identical threads and I seen the other have exact concerns and probable questions as I too would follow up with. Maybe a moderator can combine them, so anyone interested or eager can follow or join.

[YoungDiesel27]

I use a leakdown tester to better isolate where the issue is....only time a compression tester is better is for a bent rod.

[Carlosl151]

Okay thank you all. Head is getting being pulled now to do some conical springs top hat valve seals and studs. I will see the cylinder walls when the head is off. And will be able to tell if it looks like it could use a rebuild. Thanks again