Compression test results - interpretation

Fez12 · Oct 7, 2023

Series 3 diesel 5brg 1982. Engine warm,

No 1 cylinder Dry 340psi Wet 400psi
No 3 cylinder Dry 380psi Wet 400psi
No 4 cylinder Dry 360psi Wet 400+ psi

I could not do number two as need elbow. That's now on order. No 4 showed strange result wet, think gauge playing up however figure well above 400psi.

So question is does it need new rings to balance dry and wet results. Any advice welcome.

lynall · Oct 7, 2023

I would see what number 2 says, and if it is the ball park of the other three, then that would be good enough in my book.
All wet really tells you is, if that cyl is low and it improves wet then you know its rings/bore that are the issue, if it stay lows wet then you know it's valve or gasket related.
In a nutshell it they are all much the same then that is good enough, unless you are hunting a specific issue.

Fez12 · Oct 7, 2023

Thanks for reply, no specific issue, Cyril seems to be losing a little bit to much oil. I am convinced it burning some, the rest is probably leaking but Cyril not dripping oil except for a leak on front left of cylinder head but figures seem good.

lynall · Oct 7, 2023

Fez12 said:
Thanks for reply, no specific issue, Cyril seems to be losing a little bit to much oil. I am convinced it burning some, the rest is probably leaking but Cyril not dripping oil except for a leak on front left of cylinder head but figures seem good.

What viscosity oil you running?

Fez12 · Oct 7, 2023

20/50w

lynall · Oct 7, 2023

Fez12 said:
20/50w

Thats the kiddy, at least you have not fell into the lr owners lets upgrade everything trap.

steve2286w · Oct 7, 2023

The workshop manual says for good condition 440-470psi, did you ensure the butterfly valve was fully

open to allow all the air to be sucked in, happy gauge was accurate ?

if you want to investigate further then head off and sump off, check for wear ridge at top of cylinder and and after removing piston check rings in bore for gaps with feeler gauges

Fez12 · Oct 7, 2023

Cheers, Steve yes butterfly fully open, but did have all injectors out. Reasonable content it OK, hoping when I remove head that I can hone cylinders and fit new rings without reborn time will tell.

steve2286w · Oct 7, 2023

I got to that point and measured about .005” wear which you could feel on the fingernail at top decided I would. Go for rebore , prior to that was starting and running ok part for a bit smoky, it’s currently on a stand in garage waiting for a test start while running a 200di in landy
can’t recall what my pressure reading were probably not as high as yours so should still be ok
new rings and hone done fairly easily engine in situ

Compression test results - interpretation

Fez12

New Member

lynall

Well-Known Member

Fez12

New Member

lynall

Well-Known Member

Fez12

New Member

lynall

Well-Known Member

steve2286w

Well-Known Member

Fez12

New Member

steve2286w

Well-Known Member

Similar threads