Compression test #'s

[JHILL]

1st time on a diesel.
Truck has mods in sig and 332k on it. thinking I may have a valve or valve seal issue, ie oil leaking in causing the high numbers on #1 & #8.

#1 450
#2 400
#3 397
#4 415
#5 403
#6 410
#7 390
#8 440

Test was done with all glow plugs out,
5-7 comp strokes until highest reading achieved. purged oil from glow plug removal before testing, motor was not stone cold but not hot either.

For that have done before any insight is appreciated.
-Jeff

 

[SEABEE08FX4]

Your still with in spec, as far as lowest acceptable readings (any lower than 380 would be bad). But you do have quite the spread between cylinders (390-450) and thats more than likely worn valve guides with that big of a drop between cylinders and any exccesive amount of oil in the cylinders.

 

[JHILL]

Thank's,
Blow by is not terrible,with 300k+ on the clock. It may be time to pull the heads and have them gone thru. any reservation's on rebuilding the top end only to have the bottom end cause issues afterwards? It been some years since I have had any machine work done. IIRC that used to be the case

 

[neverkickn]

Does it smoke or idle funky? Does it fire quick when cold?

 

[SEABEE08FX4]

Thank's,
Blow by is not terrible,with 300k+ on the clock. It may be time to pull the heads and have them gone thru. any reservation's on rebuilding the top end only to have the bottom end cause issues afterwards? It been some years since I have had any machine work done. IIRC that used to be the case

Valve seal are cheap and can be done with the heads on, just bring each cylinder to TDC when you install them so you don't drop a valve. Once done do the compression test again and go from there. That will tell you the shape your rings are in before pulling the heads or even needing to.

 

[JHILL]

No smoke, Idle is fine now, had a tuning issue that Jonhathan @ BDP has since taken care of, waiting for Cale's tunes as well. Cold or Hot start it fires right off.

 

[JHILL]

Originally Posted by SEABEE08FX4
Valve seal are cheap and can be done with the heads on, just bring each cylinder to TDC when you install them so you don't drop a valve. Once done do the compression test again and go from there. That will tell you the shape your rings are in before pulling the heads or even needing to.

Kicking myself in the a**, I did not replace them when I did springs and studs a year and half ago. :cursing:

 

[neverkickn]

No smoke, Idle is fine now, had a tuning issue that Jonhathan @ BDP has since taken care of, waiting for Cale's tunes as well. Cold or Hot start it fires right off.

If that is the case then why not just run it:shrug:

 

[Arisley]

Old school tech here. Squirt a tablespoon or so of oil in each cylinder and retest, If numbers improve, it's the bottom end, if they stay the same, it's the top end.

 

[SEABEE08FX4]

Originally Posted by SEABEE08FX4
Valve seal are cheap and can be done with the heads on, just bring each cylinder to TDC when you install them so you don't drop a valve. Once done do the compression test again and go from there. That will tell you the shape your rings are in before pulling the heads or even needing to.

Kicking myself in the a**, I did not replace them when I did springs and studs a year and half ago. :cursing:

I wouldn't kick yourself, its an easy job and should only take you a few hours. No harm no foul, and hey valve seals are cheap.

 

[CSIPSD]

Your still with in spec, as far as lowest acceptable readings (any lower than 380 would be bad). But you do have quite the spread between cylinders (390-450) and thats more than likely worn valve guides with that big of a drop between cylinders and any exccesive amount of oil in the cylinders.

Been running a motor with 340-320 for over 18 months now...

Fires right up...

 

[SEABEE08FX4]

Been running a motor with 340-320 for over 18 months now...

Fires right up...

It's still out of spec, I didn't say it wouldn't run. I know it has to be down on power though and I bet is using some oil between changes.

 

[CSIPSD]

It's still out of spec, I didn't say it wouldn't run. I know it has to be down on power though and I bet is using some oil between changes.

No oil usage, but the oil gets black as coal in just 2000 miles or so... I'm just playing.

Keep in mind compression numbers change with altitude, mine were taken at 3500'... Sea Level the numbers would be about 350 or so.