3.0 compression check tell me I have hope

[thejeep007]

Well boats be running rough this year and last I guess. Number 4 wasn't kicking had spark so ran a compressiontest. Hope the tool was little off. Readings in psi from 1_4. 70, 70, 90, 0. Gunna pull the head and see what's goin on. Hope I head gasket will make her happy enough. Any thoughts would be appreciated. It's a 89 3.0 mercruiser.

 

[bonzoscott]

Re: 3.0 compression check tell me I have hope

I would think there would be "some" compression even with a bad head gasket. More likely stuck open valve/s. Pull valve cover and verify all are moving / working while cranking before pulling head. You may have to pull head and repair a bad valve anyway, but easy enough to check.

 

[thejeep007]

Re: 3.0 compression check tell me I have hope

Good thinking. Any thoughts on the other cylinder compressions?

 

[PatrickBoyle]

Re: 3.0 compression check tell me I have hope

If those compression numbers are correct you've got some serious issues. Even if they're wrong you've got some serious issues in #4. Like bonzo said, it's either a damaged valve or a hole in the piston. Good luck, let us know what you find.

 

[aerobat]

Re: 3.0 compression check tell me I have hope

did you apllied full throttle on the compression check ?

 

[thejeep007]

Re: 3.0 compression check tell me I have hope

Negative. Closed throttle on test. Gunna pull the valve coverin a few, iI'll post what I find. Thanks

 

[Don S]

Re: 3.0 compression check tell me I have hope

Here is how you do a PROPER compression test.

View attachment 97-25 Compression Test.pdf

 

[PatrickBoyle]

Re: 3.0 compression check tell me I have hope

The throttle plate thing is rubbish. If the engine can get enough air to idle with the throttle plate closed, it's getting enough air for a proper compression test. The most important thing that a lot of folks miss, is to remove all of the spark plugs when doing the test.

 

[thejeep007]

Re: 3.0 compression check tell me I have hope

Got it off. Lookin around see what's goin on. Here is cylinder 4

 

[Don S]

Re: 3.0 compression check tell me I have hope

The throttle plate thing is rubbish.

No, it's not rubbish, and it's not about the air. When you crank the engine with the throttle closed, it will suck fuel out of the carb and give possibly incorrect readings.
That's why on EFI engines you disable the ignition and the fuel pumps.

 

[Idlespeedonly]

Re: 3.0 compression check tell me I have hope

Looks like a lot of pitting on the intake valve. Do the others look the same?

 

[thejeep007]

Re: 3.0 compression check tell me I have hope

More cylinder 4

 

[PatrickBoyle]

Re: 3.0 compression check tell me I have hope

Does piston 4 move normally (as in, in sync with cylinder #2 with full stroke) when you turn the crank? It may be a reflection, but those wear marks on the bore look odd.

 

[thejeep007]

Re: 3.0 compression check tell me I have hope

More cylinder 4. That's bottom of head gasket between 3-4

 

[Idlespeedonly]

Re: 3.0 compression check tell me I have hope

Lots of water in the cylinders at some point.

 

[thejeep007]

Re: 3.0 compression check tell me I have hope

Seems to move fine art with the rest of em....

 

[Don S]

Re: 3.0 compression check tell me I have hope

You have been getting water in it for some time. The pistons have all been steam cleaned. I would bet you had a valve stuck open from rust that caused the 0 compression reason.

 

[thejeep007]

Re: 3.0 compression check tell me I have hope

Definitely water in there at some point. Pervious owner maybe.. Not sure where to go from here....

 

[Don S]

Re: 3.0 compression check tell me I have hope

Had you not pulled the head, you could have done some other testing to find out where the problem is. Now your kind of stuck looking for obvious things you can see.

 

[thejeep007]

Re: 3.0 compression check tell me I have hope

Don't have much time off from work so jumped in. Getting a spring compressor now let you know what's behind it. Thanks fie