Compression Test HELP

[Sydison]

Im looking at purchasing a boat 330 SeaRay Sundancer and the port engine is new ( has 60 hrs on it ). I had a compression test done it and it is as follows.

Cylinder PSI
1 130
3 140
5 110
7 140
2 135
4 140
6 120
8 130

The mechanic who did the test stated since the engine was so new that the two cylinders that showed lower PSI ratings were probably not fully seated yet or broken in. Can anyone please help in clarification on this test and if there is any truth to that statement ?

I appreciate any help in advance

 

[BruceK]

IMO all those are low for a 60 hour 4 stroke gasser. I'd expect to be seeing around 160psi, however they are all within tolerance and "balance"

 

[jrudge]

I would understand what “new” means.

new from box/ reman / nice cost of paint

 

[vas]

would be nice to give us the values for the 1000h stbrd engine as well, no?
if the other is at 160...

 

[volvopaul]

Im looking at purchasing a boat 330 SeaRay Sundancer and the port engine is new ( has 60 hrs on it ). I had a compression test done it and it is as follows.

Cylinder PSI
1 130
3 140
5 110
7 140
2 135
4 140
6 120
8 130

The mechanic who did the test stated since the engine was so new that the two cylinders that showed lower PSI ratings were probably not fully seated yet or broken in. Can anyone please help in clarification on this test and if there is any truth to that statement ?

I appreciate any help in advance

I’d expect to see at least 200 psi .
comp test only tells you something if there is a massive imbalance between the reading.
cylinder leakage test is the proper way to ascertain an engine condition

 

[rogerthebodger]

cylinder leakage test is the proper way to ascertain an engine condition

A cylinder leakage test can also indicate what is causing the lower cylinder compression pressure.

 

[Sydison]

This was a crate motor ....Chevy 350

those who asked about the starboard engine...813 hrs on it

1-160
3-155
5-150
7-155
2-160
4-165
6-160
8-160

 

[BruceK]

160. That's more expected

 

[julians]

Presume the test was done with the engine fully up to temperature?

If you do it cold you can get low values.

 

[vas]

and I was told you have to be WOT on petrol engines?

 

[BruceK]

Presume the test was done with the engine fully up to temperature?

If you do it cold you can get low values.

I have presumed cold testing unless this was done on the water after a run which I think unlikely in the tight confines of a 330 engine bay

 

[Sydison]

This was a COLD test indicating numbers under the cold testing conditions. Should a test be done when engine is at normal temp ?

 

[QBhoy]

Few things here.

presuming it’s the expected 5.7 vortec...a new and warm engine will be about 160 at its peak usually. If it’s cold you will only ever get a rough indication of health at best.
All I would say is that perhaps question if the engine has ever had water through it by means of a corroded manifold or similar. These are famous for have valve issues after such things and will certainly show a little low on compression if so.
Another thing that will show low compression on these are the condition of the oil. If it’s had crap quicksilver 25w40 in it, that oil can break down very quickly. Especially on carb variants if ran at idle for too long with no load on it. A prime example of why this would be the case on one engine and not the other, would be if that engine had the hot water heater tapped into it. Then the owner may have ran that engine at idle under no load for ages to get water heated.