Compression Test Anomaly ?

[KevO]

Have had separate yacht and specific engine surveys done on a potential new to me boat. Engine is a VP 2003 (and yes the DB Marine hex mod has been done :encouragement, Engineer says that the compression test shows 230 psi on cylinder 1 and 270 psi on cylinders 2 and 3. That seems quite a large difference. to me and I’m awaiting a more detailed report. In the meantime... Thoughts?

 

[vyv_cox]

Can be quite minor problem such as valve not seating properly to piston rings gone. Was a test done with oil in the bores? That will give a good clue.

 

[KevO]

Can be quite minor problem such as valve not seating properly to piston rings gone. Was a test done with oil in the bores? That will give a good clue.

I cannot confirm that but the engineer is a well respected and much recommended chap (including by the yacht surveyor) so I think I can trust he knows what he was doing. I’m waiting for the full report.

 

[colind3782]

Can be quite minor problem such as valve not seating properly to piston rings gone. Was a test done with oil in the bores? That will give a good clue.

+1

 

[RichardS]

+1

I believe that the recommended difference between best and worst is normally supposed to be 10% .... but, in my experience, it is not that unusual for older engines to have 20% or more difference and still run perfectly well. If the engine starts well, runs well, doesn't use excessive oil and doesn't smoke other than on initial start-up, then I wouldn't worry about it. However, you could justifiably use it as a negotiating tool.

Richard

 

[rogerthebodger]

Have had separate yacht and specific engine surveys done on a potential new to me boat. Engine is a VP 2003 (and yes the DB Marine hex mod has been done :encouragement, Engineer says that the compression test shows 230 psi on cylinder 1 and 270 psi on cylinders 2 and 3. That seems quite a large difference. to me and I’m awaiting a more detailed report. In the meantime... Thoughts?

A cylinder leakage test can help indicate where the problem is (valves , rings, gasket,etc)

 

[Old Bumbulum]

A cylinder leakage test can help indicate where the problem is (valves , rings, gasket,etc)

+1

 

[Jim@sea]

If the engine was cold when the first compression test was done there could have been less compression as there would be less oil in the cylinders.
Then when the second cylinder was tested there would have been more oil in the cylinder bores thus more compression etc.
(perhaps I am clutching at straws to think of a solution)
Perhaps if you had another compression test starting at the furthest cylinder you could find that the last cylinder (being 130psi) may be higher.
Certainly the difference is too large to ignore.