OMC 175 Low compression in one cylinder bank? Head (or gasket) failure?

[eddievanhalen]

Hi,

I recently purchased a 1977 twin OMC Formula. The units are 302 Fords (OMC 175).

The first time I took it out, I noticed some blow-by coming from the starboard engine breather cap. The engine wouldn't stay running for more than 15 minutes or so, then it would die. It would restart 30-45 minutes later or so, then die again after running 15 minutes.

I just got through doing a compression test on the starboard engine and the results have me a bit puzzled. The starboard cylinder bank (Cyl 1-4) has even compression, 120# across all four. The port side (Cyls 5-8) reads:
#5 - 60, #6 - 90, #7 - 90, #8 - 110. So, I know 5-7 are dead. I squirted some oil in the suspect cylinders and it made no difference in compression measurements. Since the starboard side has even compression and I have one good cylinder in the port side, I'm assuming rings aren't the culprit.

I'm leaning toward head gasket failure or cracked head at this point since the bad cylinders are adjacent to each other. Oil looks clean as far as I can tell. I guess I won't know until I pull the head, but does anyone have any ideas?

Any ideas would be appreciated!!

Thanks!

 

[paulie0735]

Re: OMC 175 Low compression in one cylinder bank? Head (or gasket) failure?

I was presented with one of those many years ago with a similar issue. After a leak down test revealed nothing I pulled the head and found 3 pistons not reaching the top of the bore........ due to slightly bent conrods.

 

[WillyBWright]

Re: OMC 175 Low compression in one cylinder bank? Head (or gasket) failure?

Head gasket or valve(s).

 

[ziggy]

Re: OMC 175 Low compression in one cylinder bank? Head (or gasket) failure?

i had adj. cyl. in my l6 low like that. i did a air leak test to decide what to do next. knew it was gonna lead to tearing it apart but wanted to know what to look for. air leak test indicated head gasket and it was. what it didn't show was the crack in the block in the front port headbolt hole. but the test did lead me in the right direction as to what to look for.......
since a shot of oil in the combustion chamber didn't bring compression up. i'd agree with wbw. headgasket or valves......hopefully.......

 

[whywhyzed]

Re: OMC 175 Low compression in one cylinder bank? Head (or gasket) failure?

I was presented with one of those many years ago with a similar issue. After a leak down test revealed nothing I pulled the head and found 3 pistons not reaching the top of the bore........ due to slightly bent conrods.

cool!
makes sense - 1 bad exh manifold caused hydrolocks.