Bad compression in one of my cylinders. Any hope?

chistedude

Cadet
Joined
Apr 2, 2013
Messages
9
Hey everybody,
Alright, 2001 3.0 mercruiser. Been trying to get it to start up for past month and a half or so after I realized my engine had filled up with rain water. I rebuilt the carb, new fuel pump, dis cap and rotor, oil changed, all of which it needed, still won't run. I did a compression check and got bad news. Results were:
Cyl 1: 170
Cyl 2:135
Cyl 3: 85
Cyl 4: 150

So obviously now i realize it won't start due to bad compression, specifically no. 3. I've tried to doctor it up w some oil on top of the cyl, no good, and just yesterday i treated it with about half a can of fogging oil, tried to start it again today, still won't start. I plan on continuing that until the can is gone, trying to go by the theory of motion and lotion to get it going. But I'm starting to lose hope.
Anyone have any ideas? If it comes down to having to replace the piston rings, I'm not too sure if it'll be worth it.
Thanks!
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
71,016
Re: Bad compression in one of my cylinders. Any hope?

Hey everybody,
Alright, 2001 3.0 mercruiser. Been trying to get it to start up for past month and a half or so after I realized my engine had filled up with rain water. I rebuilt the carb, new fuel pump, dis cap and rotor, oil changed, all of which it needed, still won't run. I did a compression check and got bad news. Results were:
Cyl 1: 170
Cyl 2:135
Cyl 3: 85
Cyl 4: 150

So obviously now i realize it won't start due to bad compression, specifically no. 3. I've tried to doctor it up w some oil on top of the cyl, no good, and just yesterday i treated it with about half a can of fogging oil, tried to start it again today, still won't start. I plan on continuing that until the can is gone, trying to go by the theory of motion and lotion to get it going. But I'm starting to lose hope.
Anyone have any ideas? If it comes down to having to replace the piston rings, I'm not too sure if it'll be worth it.

Thanks!

Ayuh,... Welcome Aboard,... With that much oil added, I'd sooner think ya got a Valve problem,...

Addin' oil would help seal the rings, atleast temporarily raisin' the compression,...
If that Ain't happenin', ya look to Bad Valves....

Yank the Head, 'n drag it on over to yer local Machine Shop... They'll tell ya how Bad it's gonna hurt,... ;)
 

Hoosmatroos

Petty Officer 1st Class
Joined
Jul 11, 2011
Messages
250
Re: Bad compression in one of my cylinders. Any hope?

Yup, oil doesn't help to stuck valves.
 

chistedude

Cadet
Joined
Apr 2, 2013
Messages
9
Re: Bad compression in one of my cylinders. Any hope?

So yall think it could be A valve? How would the rain water affect it so? I'm up for any ideas so I'll definately be looking into it? Is there anyway to test this theory before removing the whole head? And also, let's say this one cylinder is completely screwed, by means of rings and or valves, would the engine at least be trying to start? Because it acts like none of them are even trying to fire, keeping in mind new plugs gapped correctly and rotor and cap and proper fuel delivery...
 

chistedude

Cadet
Joined
Apr 2, 2013
Messages
9
Re: Bad compression in one of my cylinders. Any hope?

And can anyone point me in the direction of a good walk through on how to pull the head.
Thanks!
 

Fishermark

Vice Admiral
Joined
Oct 19, 2003
Messages
5,617
Re: Bad compression in one of my cylinders. Any hope?

Pulling the head is easy, but before you do that, have you checked to see if you have spark?
 

chistedude

Cadet
Joined
Apr 2, 2013
Messages
9
Re: Bad compression in one of my cylinders. Any hope?

Also, any input on timing possibly making this issue? I haven't done anything to change it but I mean if there's no stark at the right moment, no fire right?
 

chistedude

Cadet
Joined
Apr 2, 2013
Messages
9
Re: Bad compression in one of my cylinders. Any hope?

Ya I've checked for spark with a neon spark tester, spark at every cylinder.
 
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chistedude

Cadet
Joined
Apr 2, 2013
Messages
9
Re: Bad compression in one of my cylinders. Any hope?

So I'm getting fire now, but it won't stay running as soon as I stop turning the key. Any suggestions?
 

Speakrdude

Ensign
Joined
Feb 25, 2004
Messages
942
Re: Bad compression in one of my cylinders. Any hope?

Change the ignition switch, or simply hot wire it to test. Have had many switches go bad and only energize the circuit while in the start position.
 
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