Opinions needed - Valve job or new motor?

[edsmax]

While changing out my exhaust manifolds, I noticed some rust in the exhaust ports of cylinders 3 & 5. This was due to water seepage from a failing manifold gasket.

Asked marina service to run compression and leak down tests. Cylinder 3 is at 105lbs, cylinder 5 is at 30lbs. Boat ran fine all last year. Service manager is going to look at overall condition of motor and give me my options. Motor is original and has approx 600 hours. He said an option is to take head off and do a valve job. Think this will fix the problem? I am awaiting his estimate on the cost of this vs reman engine vs new mercury. Any opinions or experience appreciated.

Ed

 

[rondds]

I'm thinking you need to pull the heads to see if the problem is in the block or the heads. If the cylinders are not scored in the block, have the heads done ($180 per side) and put things back and you should be OK. You can learn a lot more with the heads off and make a better decision about what's actually the problem.

 

[OldSkool]

600 hours is not a lot of hours for a small block GM. You need to remove the head to see if the cylinder itself is damaged. If the cylinder and piston are good then a valve job may be the best fix. Have the head tested for cracks as the water can come from a cracked head as well as a manifold gasket leak.

You'll need to count the cost of reman or rebuild by your mechanic on what is best if an engine is needed. If you do replace with reman then the onus of liability/warranty is with the engine rebuilder rather than the mechanic. (Recommended)

 

[OldSkool]

Ron, Looks like you got in a click ahead of me. As you can see by my post, we are thinking along the same lines.

 

[douglee25]

You need to run a leak down test now before you go any further. If it's leaking at the valves, you will hear it coming out the ports. If that's the case, there's a good chance the valve job would fix it.

Doug

 

[edsmax]

Leak down test was performed and it was leaking through the port. This has been confirmed already.

 

[douglee25]

Then if it's leaking through the port, I'd do a valve job.

If you're mechanically inclined, you should be able to tear it all down relatively easy to save some cost. Send the head to the shop for the valve job, and then have the marina reassemble.

Doug

 

[Happy Hour IV]

Only have experience with 454's but, are you sure water was from a failing manifold gasket ? It would seem to me that a failing
manifold gasket would only leak exhaust since there is no water on either side of the gasket normally

 

[douglee25]

I think the OP meant to say a failed riser gasket, not a failed manifold gasket. A failed riser gasket will leak directly into the exhaust ports.

Doug

 

[edsmax]

Correct; it was actually the riser gasket that appears to have weeped allowing water to settle in the area you see in the picture.

 

[300SR]

600 hours is not a lot of hours for a small block GM. You need to remove the head to see if the cylinder itself is damaged. If the cylinder and piston are good then a valve job may be the best fix. Have the head tested for cracks as the water can come from a cracked head as well as a manifold gasket leak.

You'll need to count the cost of reman or rebuild by your mechanic on what is best if an engine is needed. If you do replace with reman then the onus of liability/warranty is with the engine rebuilder rather than the mechanic. (Recommended)

I agree pull the heads take ya 2Hrs tops

 

[techmitch]

Then if it's leaking through the port, I'd do a valve job.

If you're mechanically inclined, you should be able to tear it all down relatively easy to save some cost. Send the head to the shop for the valve job, and then have the marina reassemble.

Doug

So he should tear it down himself and then ask the marina to reassemble? REALLY...

 

[edsmax]

So he should tear it down himself and then ask the marina to reassemble? REALLY...

I think he was giving me advice on saving money (a good thing). I am going to leave the head R&R to the marina as well as installing the new exhaust manifolds. Ideally, I want this to solve the problem so I can get the boat on the water in time.

 

[rondds]

Guys
Let this be a lesson to us all. THE weak link in the system with these Mercs, whether they be 350s, 305s or 454s, is the stupid riser/elbow gasket. These MUST MUST be prophylactically replaced at least every third season. It's a $10 item and an hour or three, depending on how many engines you have and if there's a riser involved or just an elbow. They are the single leading cause of catastrophic failure of these engines. It happens time and time again!

 

[douglee25]

So he should tear it down himself and then ask the marina to reassemble? REALLY...

Yeah, really?

What's the issue? I'm sure the marina is already busy as Hell.... so what if the owner wants to save a few bucks on the tear down.

Doug

 

[SCORPIO]

How old are your risers and is the boat raw water cooled? If they are older than 4 seasons now would be a good time to replace them, cheap insurance.

 

[Air O'Nautical]

Yeah, really?

What's the issue? I'm sure the marina is already busy as Hell.... so what if the owner wants to save a few bucks on the tear down.

Doug

I get it....and agree.
The tech trying to reassemble what you took apart wont work.
Nobody would do it.
I just went through this job last summer and you end up with nuts and bolts all over the place.
"I" knew where it all gos back only because, I took it apart.

If you are a shade tree mechanic its an easy job.
It is an honest half days work to remove and another one to reinstall (taking the required beer breaks).
There is alot of accessory's to remove from the motor, and it all takes time.
The positions you need to work in are the type you feel the next day!

I agree do the heads and go boating...600 hrs is nothing.

Cheers.

 

[cod]

If the boat ran fine last year, I would say it's not a cracked head as I think you would have a rough running engine with water fouling the plug. There would also probably be water in the oil(milky color). The mainfold/riser connection is a poor design by Mercruiser and its amazing it hasn't been redesigned after all these years. If the riser had a sleeved port for the water jackets that slipped inside the mainifold, you almost wouldn't need a gasket. (Just thinking out loud). Most people probably don't even realize they have this problem, and yes the boat will run fine with maybe a loss of top end speed. As others have mentioned, the valve job should fix the problem, but there is also the possiblity that if the piston ring rusted to the piston(you won't be able to see that) or damage occured to the cylinder wall, after you do the valve job, and compression is back to spec.,you may start burning oil on that cylinder and it will foul the plug.

 

[edsmax]

If the boat ran fine last year, I would say it's not a cracked head as I think you would have a rough running engine with water fouling the plug. There would also probably be water in the oil(milky color). The mainfold/riser connection is a poor design by Mercruiser and its amazing it hasn't been redesigned after all these years. If the riser had a sleeved port for the water jackets that slipped inside the mainifold, you almost wouldn't need a gasket. (Just thinking out loud). Most people probably don't even realize they have this problem, and yes the boat will run fine with maybe a loss of top end speed. As others have mentioned, the valve job should fix the problem, but there is also the possiblity that if the piston ring rusted to the piston(you won't be able to see that) or damage occured to the cylinder wall, after you do the valve job, and compression is back to spec.,you may start burning oil on that cylinder and it will foul the plug.

Thanks - When I changed the oil last fall before winterization, it looked fine. This may explain why I was never able to reach the same top ends as others claim to reach with the same basic package. Highest I top out at is 35-36 mph GPS verified. All plugs looked ok when I pulled and changed them, just high wear. New OE manifolds and gaskets about to go in too (once valve job is complete, obviously).

 

[tdschafer]

I agree with all above. 600 hrs is low , even if it's RWC and a valve job will be ALOT cheaper than a new motor. Heads and manifolds/risers and get back to boating!!