Thoughts On This Compression Test (2003 SAN w/ PCM 330)

[KDenning]

Hey All!

If you've seen my thread in the Boats Wanted, section you'll know that we sent a potential boat to have a pre-purchase inspection performed today.

Everything came back as-expected with nothing out of the ordinary per the technician. They provided me with the following compression numbers:

1. 135
2. 145
3. 135
4. 145
5. 135
6. 145
7. 135
8. 145

Thoughts?

I've read previous posts regarding the highest number and lowest number being within 10% of one another but maybe someone can shed some light on these numbers relevant to a 2003 PCM Ex 330? Is there anything else we can infer from these numbers?

Thanks in advance!
Kirk

[hal2814]

Looks pretty good for a 20 year old engine.

[bturner]

I don't think I've ever seen results like that. You have 4 @ 135 and 4 @ 145. Not sure what's more odd, the values or the pattern. Are the cylinder numbers the firing order or the number of the cylinder? If the description below is correct, all the cylinders on the left are low by 10 psi, exactly. Not saying I do this on a regular basis but when I have the numbers have varied quite a bit more than what you have here.

"The firing order of a Chevy 350 V8 engine is arranged from the front of the engine to the back, starting at the driver's side.¹ The cylinders are numbered from left to right, with all the odd-numbered cylinders on the left and all the even-numbered cylinders on the right"

As far as the results go, if you believe them, they are all within 10% and all in what I would consider normal values for a 20 YO engine. I honestly would be more concerned on if they're correct. If you trust the shop, well, I guess you got that 1 in a million engine with those compression values.

But who knows, maybe this happens all the time with a 20 YO engine and I'm completely wrong.....

[KDenning]

bturner that’s what I found odd as well….

Heres what I got from the pre purchase inspection. Unfortunately the boat is ~12 hours from me so I need to figure out how to interpret this based on that report (which I’m disappointed in visually with the sloppy writing lol)

[jpwhit]

Those are good numbers for an EX330 or EX343. Don't over analyze it......

[KDenning]

jpwhit that's what I needed to hear! I'm happy with everything else that I know about this boat regarding the condition so I'm trying not to get hung up on this one thing which is probably just a numerical anomaly right?

Thank you for the feedback!

[jpwhit]

Compression numbers are never the same from cylinder to cylinder. That's about as good as it gets for an engine with any age. There are so many reason that the pressure vary some, that it's not even worth discussing.