Compression Test?
 

I'm looking to buy a 2001 Wellcraft Excalibur 260 and found a nice example online with low hours and a 502/415/B1. The boat is out of state so I had a Mercruiser rep come down and to a mechanical survey. He stated the following:

"ALL MECHANICAL POINTS OF INTEREST ON THE 502 MPI BRAVO PACKAGE CHECKED OUT GOOD .ALL OIL LOOKED GREAT NO SIGNS OF WATER IN FUEL ENGINE OIL OR OUTDRIVE OIL

COMPRESSION ALSO IS IN STANDARD RANGE CYLINDERS ARE ALL IN SPEC.

(1) 160 PSI (2) 165 PSI
(3) 160 PSI (4) 160 PSI
(5) 165 PSI (6) 160 PSI
(7) 160 PSI (8) 160 PSI

RISER AND MANIFOLDS ALSO LOOK TO BE IN OK SHAPE . ALL OIL ARE IN NEED OF CHANGING ENGINE AND OUTDRIVE. "


I'm very confused at the compression readings. At std atmosphere of 14.7 160 psi suggests 10.88 compression ratio. Mercruiser says the 502/415 is 8.75. I would have expected compression around 128 psi. Maybe less considering cam overlap. I did an internet search on compression tests on similar 502s and numbers were in the 125 psi range

What's up? Am I being scammed?

Cheers!

not sure about the exact reading it should be, but as far as I know, first thing is they are all pretty much equal, that is the first good point, and second, generally speaking, I would think or I'm pretty sure I know compression should be around 150 to 165-170 psi.


In my opinion you have a whealthy engine, if it was 128 like you stated, I would defenatly consider a rebuilt of heads or bottom depending what causes the leak...

Other will chime in here and probably confirm what I said... hopefully!:D

Those numbers are Fine!


Do a leakdown and you will know for sure.

Those readings are fine.My 98 502mpi reads 145/150 at 6k elevation.I would imagine your tests are being done at sea level or real close.

Okee Dokee then. I appreciate the input!

You can also have a quick and inexpensive oil analysis done. They take a small sample and chemically analyze it. Show metal content, antifreeze etc.

I once did a static compression test on on my Merc425's and had higher #'s than what I thought I should had. An engine builder told me that was because I had relatively small cams and that will give me a higher static compresion pressure. Once I tore down the engines there were no radical domed pistons. He said just be worried if there is a difference between cylinders.

Thos ecomp numbers are very good. As far as your math, that does not apply to comp ratios.

Compression tester guages can be off. I have seen cheap ones that are inaccurate and expensive ones that are inaccurate. A compression test is good but a leakdown test will tell you the real story.

Ditto- those numbers are fine.