1984 OMC 200HP compression

[Logan.k]

Hey everyone.
Just went out and purchased a 1984 edson intruder with known drive issues. Unfortunately I was not able to run the engine as it's the middle of winter here. Just a a video to go off of.
My concern is once I got it home and into my garage I discovered it wasn't winterized properly.
There is a small crack in the block which doesn't seam to be affecting anything (no compression lose on adjacent cylinders and no water lose).
All cylinders read 120 +/- 1 or 2 except one which reads 90. The one that reads 90 does have moisture in it as well as the back cylinder on the other side(which still reads 120).

I should add the boat starts and run absolutely fine. Other that the drive issue.

Just curious what your thoughts are.
Is it worth attempting a head gasket?
Or maybe it's a ring issue and will losen up when it can go for an actual run.
Any advice would be greatly appreciated.

 

[racerone]

edited

 

[Scott Danforth]

if your motor is an I/O, those numbers are low

if your motor is an outboard they are not bad....except the one bad cylinder

 

[Logan.k]

if your motor is an I/O, those numbers are low

if your motor is an outboard they are not bad....except the one bad cylinder

Motor is a 1984 inbord omc V8 I belive the 305 not sure if it's a 2v or 4v. Seems to start and sound alright other that the compression on the one is way off.
I'm going to try tightening the heads tomorrow and maybe get lucky. I also read online de carbing might help.

Edit: I should add the compression tests were done cold.

Any idea what the compression should be?
I can't seem to fine any info on the 305 marine and its my understanding the marine versions had lower compression.

 

[Scott Danforth]

being a 305 V8, your compression in all holes should be 150 psi.

its not anything about tightening the heads. most likely you have rust in a valve seat.

fire it up and check after running it. if that low hole doesnt come up or all of them for that matter, do a leak-down test. you may have to pull the heads and get a head job or you may be looking at a reman.

pull the stringer drive and change the raw water pump (do a whole pump, not just the impeller). inspect the vertical drive shaft.

take care not to damage that $1000 shift cable.

check the condition of transom and stringer mounting blocks

 

[Logan.k]

Unfortunately I don't have the equipment to do a leak down test. I think I'll do as you suggested and just pull the head and take them to a shop to get machined.
Would a cracked piston wall still blow 90?
I'm assuming not so hopefully it's just a valve or head gasket issue.

Thanks a bunch!
I'll let you know what I find.

 

[Scott Danforth]

Without a leak down test, how do you know it's the head and not the rings?

No sense pulling the head and spending money until you know what the problem is.

You can borrow a leak down test kit from any FLAPS

 

[Logan.k]

Right, got a little ahead of myself and forgot rings existed lol.
How do I know if the lose of compression is going out a warn valve or rings though?
Wouldn't a leak down test just show compression loss?

 

[Bondo]

Right, got a little ahead of myself and forgot rings existed lol.
How do I know if the lose of compression is going out a warn valve or rings though?
Wouldn't a leak down test just show compression loss?

Ayuh,..... Welcome Aboard,.... A leak down test is done by bringing each cylinder to it's Tdc, 'n blowin' compressed air in through the spark plug hole,.....
If you hear the air through the carb, it's an intake valve,.....
If you hear the air from the exhaust, it's an exhaust valve,.....
If you hear the air through the oil fill hole, it's the rings,.....

 

[froggy1150]

And you can verify rings with a squirt of oil. If after getting a low reading a bit of heavy oil, enough to cover rings, and if compression comes up some.... the oil slows air. bypassing the rings. Do all three and you will know the answers

 

[Logan.k]

Hey all. Finally got a chance to run the leakdown test losing a bit of compression to rings but the majority of it is lost to the exhaust valve on that low cylinder. This is likely due to it being on the exhaust stroke over winter as it was never foged.
Looks like it'll need a head job.

Thanks for all your advice