0 compression

[Clint3240]

i did a compression test on my 260 merc today and i got 150 in all cylinders except 2. one of them has 100 and the one next to it has zero. whats up with that? blown head gasket? the engine starts right up and revs fine. this is not under a load though just in my driveway. dont hear any odd noises.

 

[JustJason]

Re: 0 compression

You really need to do a leak down test on the motor. But if you don't have the equipment pull the valve cover and see if the valves are closing. To get 0 psi you either are missing a piston, which you would hear. Or your valves are not closing for 1 of many reasons. If your valves are stuck you can try taping on them with a wooden block and hammer, it may free up. If it does it's a temp fix at best. Could be as bad as bad guides, could be as simple as carbon buildup on top of the valve. Could be tuliped from detonation. Pull the cover first and have a looksee.

 

[TilliamWe]

Re: 0 compression

Yep, you've got valve issues. And pulling the rocker cover might not show you anything. Try loosening the valves on the bad cylinders, then recheck. If compression goes up, you have tulipped valves.
Have you been "lugging" the engine? Running with a dirty/fouled bottom?

One way or another your cylinder heads are coming off. But your issue will be valves.

 

[Clint3240]

Re: 0 compression

ok thanks, i will pull the cover off. i didnt think it would be the valves becasue there wasnt to much blow back

 

[Don S]

Re: 0 compression

To get 0 psi you either are missing a piston, which you would hear.

LOL, one would think that, but I for one have seen and not heard it. The shop owner moved a boat from one marina to the ramp. Engine was down on power per customer. When we got it in the shop I started it and sure enough there was a miss. Did a compression test and 0 psi on one cylinder. Pulled the head and here is what I seen. It must have made a noise sometime because the piston was gone, and the riings were still there.

 

[meesh]

Re: 0 compression

Also could be as simple as a broken valve spring.

 

[krisnowicki]

Re: 0 compression

Guy probably just boat the boat and the previous owner said the engine was "just rebuilt"

 

[TilliamWe]

Re: 0 compression

ok thanks, i will pull the cover off. i didnt think it would be the valves becasue there wasnt to much blow back

Yeah, that doesn't seem to matter. I didn't have "blow back" on mine either, but had several tulipped valves. And the motor would still reach MAX WOT RPMs too, on just 7 cylinders!

 

[Bt Doctur]

Re: 0 compression

That a trick photo,Don. Can`t imagine that all the pieces went into the pan
and not something thru the block.Plus is must have been making a heck of a lot of clanking.