no compression in #5 on V6

[Grouchybear35]

Okay,<br /> I have finaly removed my exhaust manifolds on my OMC 4.3 V6 and they look fine. I pulled the plugs to do a compression test and the plug from #5 was missing part of the electrode. So I did a compression test. All of the other cylenders looked good but #5 was very low (10 psi max). I ran out of time working on this but at this point I am hoping for a head / valve problem. Anyone got an idea as to what I will find when I can get back in to it again and pull the head?

 

[CCrew]

Re: no compression in #5 on V6

My vote's on either a valve stuck open or burned, or a hole in the piston top.

 

[loadnet]

Re: no compression in #5 on V6

Squirt some oil in #5 and take another compression test on it.<br /><br />If the pressure increases real nice, you have a piston ring problem.<br /><br />If the pressure does NOT increase any, you have a valve issure.<br /><br />Like the man was saying, burnt, stuck open or bent valve.

 

[jlshields]

Re: no compression in #5 on V6

Grouchy, was the plug tight in the head? I ask because I had same problem with a Merc 5.7LX. The plug, also #5, wasn't tight and therefore couldn't transfer heat away causing detonation in that cylinder. Destroyed piston, scored cylinder, bent valve.<br />john

 

[scamper]

Re: no compression in #5 on V6

Does it look like the electrode broke off or burned off? If part of the electrode broke off, the thing could have bounced around in there, broke a valve and/or gone through the top of the piston.

 

[Grouchybear35]

Re: no compression in #5 on V6

The plug did not seem to be loose. I think something hit the end of the plug and took it off. But that is just my deduction thus far.