Anybody seen cylinder scoring like this?

[hrznjb]

I have a Mercruiser 350 Tournament Ski. I was running WOT when the RPMs dropped from 4500 to 3000. While the engine continued to run over the next 48 hours, it became progressively harder to start and eventually the starter failed.

We pulled the plugs and found water in the cylinders and oil pan.

After a dryout and oil flush, we still had water in the #3 cylinder. The cylinder would not hold pressure on a leak down test and airflow could be heard in the #5 cylinder.

We removed the header to find a blown gasket and a strange scoring in the #3 cylinder. I would have expected a water washout to have maybe left a straight and uniform ring score on the cylinder wall. Instead, I have a serpentine score with irregular width and depth like spalling.

My thought is that the cylinder is cracked and that steam pressue created the spalling as steam moved from the water jacket and into the cyclinder. The overpressue of the cylinder caused the gasket to blow (as a blown gasket is uncommon in this engine.)

Does anybody have thoughts on this theory or an alternative theory? How about a repair strategy (bore and sleeve vs reman long block?)

Thanks for the help.

 

[rs2k]

Re: Anybody seen cylinder scoring like this?

Picture #2 looks like it is from piston seizure. Picture #1 looks like FOD damage, but it may also be caused by a partial seizure.

The seizure explains the drop in RPM. It sounds like the gasket blew and the engine overheated which caused a seizure.

A repair will require a rebuild. Bore and hone the cylinders and replace the pistons at bare minimum. Honing won't fix marks that deep.

 

[hrznjb]

Re: Anybody seen cylinder scoring like this?

Your FOD idea is interesting. Could it have been the gasket material? But it must have been chewed up because nothing was found. As to a seizure, the piston head does not show damage or abnormal combustion patterns.

Either way, I suppose the depth of the scoring will dictate how to proceed. Am I correct?

 

[wca_tim]

Re: Anybody seen cylinder scoring like this?

was the other side dry? perhaps a leak in the exhaust manifold / riser, water in the cylinders, hydrolock, broken piston(s), blown head gasket, etc...

repair strategy: make certain you know the origin of the problem (the guy I bought my current toy from blew the engine up 3 TIMES!!! from a leaking exhaust manifold and never thought to check the exhaust, when he told me, I didn't even know what to say...), if your heads are in good shape, have them freshened up and checked, if fine, shortblock, if not fine, long block.. imho...