Possible Valve issue-gctid397274

[Guest]

I have an 87 2550 Ceria with a 5.7 OMC under the deck.

It started running really poorly the other day and upon investigating it I discovered that my number 7 cylinder has only 60 psi of compression while the other 7 cylinders are 175 plus. I squirted oil into the cylinder and the reading didn't change at all so I am assuming it is valve related.

My question is can I safely remove the head with the boat in the water or will the open exhaust system flood the boat.

Thank you.

[2850Bounty]

Yes, you should be able to remove the cylinder heads while the engine is still installed.

I'd warm the engine up prior to cracking the manifold and riser bolts loose. You don't want to risk snapping a bolt off.

You can finish up after it cools back down.

Just drain the engine coolant completely either with the side engine drain ports, or by removing the lower Circ Pump suction hose.

If raw water cooled, and if you use the side drain ports, be sure to probe them.

Remove exhaust manifolds/risers, cap off the Y-pipe ports, and cap off the sea water supply... although with the Cobra, I don't believe that this is necessary. Play it safe anyway.

If you end up replacing a cylinder head, be sure that you match casting numbers so that you end up with the same size combustion chambers.

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[Guest]

Before going that far...are you sure it's not a rocker?

There are a couple of ways to confirm a bad valve.

My favorite is to get the cylinder up on tdc compression, then apply some compressed air gradually and listen to where it's hissing. Intake and it's an intake valve, exhaust, well, exhaust, and if it's coming out the pcv/dipstick it's rings/detonation damage. It works really well.

Anyway, also pull the rocker cover (You will anyway of course) and check for a bad rocker, or a rocker nut that backed off. It could be that simple.

Chay

[2850Bounty]

cfoss wrote:
Before going that far...are you sure it's not a rocker?

Chay, good call.......... however, he's getting 60 psi of compression in number 7 cylinder.

I suppose that it could be an exhaust valve rocker arm........ it's certainly worth looking in to.

[Guest]

Maybe a broken spring... I have seen this a few times.

Most valve issues are from water incursion how are your exhaust manifolds?

[Guest]

We bought the boat used last year and this is our second season. It has 570 hours on the hour meter. The manifolds were replaced before we got it and they appear to be in excellent condition. It ran really well last year and we started off great when we relaunched this spring.

It would be great if was only a rocker are but it has been my experience that it would be rather noisy if it was. I am going to remove the rocker cover this weekend and check it out further. I'm just concerned that with the exhaust opened up I could possibly sink the boat if I removed the head with the boat still in the water. I am trying to keep costs at a minimum because money these days is a huge issue.

Thanks.

[2850Bounty]

shadowf1 wrote:
I'm just concerned that with the exhaust opened up I could possibly sink the boat if I removed the head with the boat still in the water.

If the outside water level was high enough to flow over the top of the Y-pipe, then your boat is sitting too low in the water as it is.

Marine Mechanics pull cylinder heads in larger I/B and I/O boats often. They just close off these ports as a safety measure.

If you are that concerned, place a straight edge across the gunnels and extend one end over the water.

Measure down to the water level, then measure near the engine bay down to the top of the Y-pipe.

Now do the math.

I'll bet that you have inches to spare, and then some.

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