Compression Test Results

[jdtower23]

Ran the compression test on an '88 4.3 L OMC I'm having trouble with....

160, 162, 158, 165, 156, 0

I'm not sure if the ZERO is accurate...that piston is spitting water....how can i get the water out to accurately test it? i think it's dumping in from the manifold as i crank it....tried the drain **** on the manifold and nothing but i know there is water in there......any suggestions?

How are the rest of the readings? I was pleased how close they are at least....

Thanks

 

[Don S]

Re: Compression Test Results

If you have done a compression test on the rest of the cylinders and you still have water in the cylinder, then you have a problem. You can either do a leak down test to find where all the compression is going, or take the head off. But to have 0 compression with water in the cylinder means the valves are stuck open or since the water didn't squirt out of the hole while cranking the engine, perhaps the piston isn't going up and down. Seen that happen a few times.
Stick something flexible, like a straw or a wire tie, in the spark plug hole and let it touch the piston and crank the engine over BY HAND and see if it moves.

PS: Being happy that the other 5 are good doesn't help, eventually it's gotta come apart.

 

[Haut Medoc]

Re: Compression Test Results

Ran the compression test on an '88 4.3 L OMC I'm having trouble with....

160, 162, 158, 165, 156, 0

I'm not sure if the ZERO is accurate...that piston is spitting water....how can i get the water out to accurately test it? i think it's dumping in from the manifold as i crank it....tried the drain **** on the manifold and nothing but i know there is water in there......any suggestions?

Yes, drain the entire block.....​

How are the rest of the readings? I was pleased how close they are at least....

Thanks

Well 5 out of 6 look good......
I'd bee looking at the valves on that cylinder....
Broken valve spring?
Bad seat?.....
If you can't see anything obvious from up top, you will need to pull the head.....​

 

[jdtower23]

Re: Compression Test Results

Don,

Water did squirt out of the hole....at 1st i tried to get it all out but I can't!! I think the water messed with the reading because I know it was getting some compression....it sprayed the water all the way on the inside panel of the boat, around 3 feet away....

Any ideas to dry this out?

thanks,
John

 

[Don S]

Re: Compression Test Results

Right now, a compression test is a waste of time.
I would guess one of the valves is stuck open, when you crank it over the water goes past the valve and then rolls back in.
If the valves were working, then the compression would have either been real high, or you would have had a hydrolock.

 

[jdtower23]

Re: Compression Test Results

Don,

What should be my next step? Remove manifold and valve cover and confirm that?

Thanks,
John

 

[Coors]

Re: Compression Test Results

And what is the level, and color of the oil? It may be leaking down past the rings, while it sits.

 

[jdtower23]

Re: Compression Test Results

level is fine right now....just changed it....but it was pretty high before.....another thing, i just looked under the valve cover, fresh water on the rocker arm....

John

 

[Coors]

Re: Compression Test Results

Grit your teeth, and pull the head.

 

[Don S]

Re: Compression Test Results

Did you ever do THIS test?
Then, like I said at the beginning of this thread, you need to do a leakdown test to get an idea what is leaking where. Look at page 2 of This service bulletin.

 

[jdtower23]

Re: Compression Test Results

Just completed the pressure test....i left the plugs out....don't know if that is a no-no or not but it pumped up to 15PSI then my connection broke....reconnected and suddenly i started getting a STEADY stream of water out the #1 piston....it drained for a min or 2 at least then finally hissing and air coming out that plug hole.....

What do you guys think? Cracked head?

Thanks,
John

 

[Don S]

Re: Compression Test Results

Pull the head and look.
Sounds like it's a good thing I forgot to mention to drain the cooling system first.

 

[jdtower23]

Re: Compression Test Results

Thanks for all the help guys, especially Don! I will try to pull the head tomorrow....

 

[jdtower23]

Re: Compression Test Results

Pulled the head, and almost certain it's just the head gasket! broke on both sides right in the middle of the piston and trailing signs....motor looks good inside...just need to clean up the affected cylinder....will try to post a pic later....thanks guys for the help so far!

John

 

[Don S]

Re: Compression Test Results

Check everything a second time. I have never seen a head gasket cause 0 compression. It'll drop way down, maybe 30 to 50, but there will be something there. Does the piston go up and down?

 

[jdtower23]

Re: Compression Test Results

I know for a fact the piston goes up and down....I think since I still had water in there it plugged up the line and i didn't get a good reading....I am going to have the head pressure tested just to make sure....lifter galley looks good....would it be obvious if there was a crack there?

 

[Don S]

Re: Compression Test Results

Yea, water destroys compression gauges. To actually have 0 compression, you would need a hole in a piston or serious valve problems that you could see.

 

[jdtower23]

Re: Compression Test Results

Here are a few pics of the gasket, a little out of focus but you can see what's going on.....

http://i195.photobucket.com/albums/z25/jdtower23/California021.jpg
http://i195.photobucket.com/albums/z25/jdtower23/California023.jpg
http://i195.photobucket.com/albums/z25/jdtower23/California024.jpg