How to Compression test

[sruman]

Re: How to Compression test

Can you perform a compression test by removing on plug at a time, and firing up the engine for a few seconds and revving it up a little bit?

 

[wilde1j]

Re: How to Compression test

I wouldn't ...

 

[sruman]

Re: How to Compression test

why not? Just trying to understand the dynamics and risks associated with this? Obviously, water will be connected? Will it give false readings? Damage tester? Harm engine? Details, I need details.........LOL.

 

[turtles11756]

Re: How to Compression test

excellent answer about gas in the holes

 

[Sea18Horse]

Re: How to Compression test

The way the schraeder valve core in the tester works, in an engine running at idle speed the "pulses" of pressure come too fast for the schraeder valve to keep up. And your reading will always be low.

Now a "running" compression test does have its uses in an automotive application (or any four stroke engine for that matter) when you are looking for a strange valve train problem. Broken valve spring, flat cam lobe or some other anomoly. But it's used in conjunction with a standard compression test to suppliment your information. Not on its own.

Cheers...............Todd

 

[sruman]

Re: How to Compression test

Now we're talkin'. Thanks for the insight.
Now, on another note, I bought an 82 Johnson 150 hp with a 14.5 x 22 prop. Can't get the RPM's (or speed) up when on the water. Is it a prop issue? I can only get about 3800 RPM. Thoughts? Out of the water, the engine seems to rev normally, and compression tests come back at about 135, give or take 5. Doesn't miss, runs smooth, just don't seem to have power to push it over the edge. Any tests to run?

 

[wilde1j]

Re: How to Compression test

Two points
1) You haven't said anything about the boat and loading, so it's not possible to comment on the prop, although your motor needs to turn 5800 RPM @ WOT. 3800 is WAY too low. The only "test" I can think of is putting the motor on a dyno to verify it's HP output, but you won't find too many dealers with one. A 22" pitch prop is generally suitable for pretty light boats, say like an 18' max bass boat. BTW, running on the hose tells nothing and running up the RPM unloaded above 2000 is a good way to create a really ugly paperweight.
2) You'd get a better response by starting your own thread ... more people will potentially respond.

 

[sruman]

Re: How to Compression test

Thanks for the info. The boat is an 18' Astroglass, about 1100lb. Add my fat butt for another 250 plus tackle and cooler, 100lbs. 1500 total lbs. Could it be electrical? Maybe. Compression seems good. Could it be reeds? Maybe. I was hoping a 22 pitch prop was like running in high gear all the time. And not enough hp to get it up to full speed, top RPM. Again, engine runs smooth, just doggy.
Good advice on the 'new thread'. I probably should (and will) if I need to continue posting. I'm mainly a reader and find most of the answers without posting. Thanks again.

 

[jonesg]

Re: How to Compression test

" I'm mainly a reader and find most of the answers without posting. "

Makes it difficult to give back if all you do is take.
Too many posts scroll off without any reply to their questions.