Compression test

[matuva]

Good day all,

what is the good value I must find when doing a compression test on the 6.5? is it in the range of 350-400psi.?

 

[bison]

380 to 400, hot engine.
Do the test twice,second time with a squirt of oil trough the plug hole.(spin the engine before taking the test to blow out exess oil)
The second test is to check ring health.

 

[ak diesel driver]

IIRC 300 is the low end according to our 84 FSM for a 6.2

 

[matuva]

Wow, that's fine.

I just received the data sheet from an engine I just bought at Ted's engine, and it shows an average of 520 psi. Minest is 515 psi (#1), highest is 535 psi # 4 & 8)

 

[OrionThade]

My Ted's engine tested at:

Front of Engine
1. 530 2. 530
3. 515 4. 525
5. 515 6. 515
7. 520 8. 520

 

[NVW]

Has anyone done their own comp. tests to verify Ted's?

 

[OrionThade]

I don't have a diesel comp tester. I didn't then, either. Had the condition of the cylinders been suspect, I would have suspected the compression test. If you find my build thread, you'll see how clean the internals were.

 

[NVW]

I was just curious.

 

[bison]

500 is kinda high IMO but i guess it's attainable when one tests one jug at the time with running engine on the 7 others.
I don't think one gets that high compr with just the starter turning the mill,..I never could.

 

[OrionThade]

500 is kinda high IMO but i guess it's attainable when one tests one jug at the time with running engine on the 7 others.
I don't think one gets that high compr with just the starter turning the mill,..I never could.

Yep, that makes sense.

I think the more important thing to look for when running a compression test manually turning the engine over is consistency across all cylinders, right?

In other words, if by turning by hand we see:

1 - 300 2 - 300
3 - 300 4 - 300
5 - 300 6 - 300
7 - 300 8 - 300

This would indicate that we don't have an issues with any one cylinder, vs:

1 - 300 2 - 300
3 - 300 4 - 300
5 - 300 6 - 100
7 - 300 8 - 300

which would indicate that something is wrong with Cyl 6 and would warrant further investigation.

Right?

IIRC, a cylinder can have a 25% variance in compression PSI, which is pretty high I think.