Merc 3.0 Low Compression 2 & 3

[tschmidty]

OK, so sounds like the head gasket is blown between 2 & 3 which seems to be a common problem. Compression test gets 135, 85, 80, 130. Couple questions before I tackle it. Engine runs good, no water in oil, etc.

1. Am I confident enough to just order a head gasket and rocker cover gasket and have at it? Ie, order those before I tear it apart

2. If I don't remove the exhaust manifold, can I get away with just those two?

3. Thoughts on which gasket set to get, Sierra, Fel-Pro or OEM Mercruiser (which is not popping up online)?

Thanks in advance

 

[Bifflefan]

Re: Merc 3.0 Low Compression 2 & 3

No, you need the intake and exhaust gaskets also, here's why.
There is a reason why the head gasket blew. More than likely the head has some warp and will need machined. Once the head is off, lay a straight edge on the surface, If you can see any light under it, it needs machined.
Granted that is not all the steps, but you get the idea.
As for the gasket brand, Fel-pro probably made it and Sierra stamped their name on it.

 

[TilliamWe]

Re: Merc 3.0 Low Compression 2 & 3

I'll bet you a nickel that it's not a headgasket. I'll bet you its an exhaust manifold/riser issue. Either way, take the exhaust off and check it out very closely.

 

[fat fanny]

Re: Merc 3.0 Low Compression 2 & 3

After removing the mani and then the head lay a straight edge across every surface if you have no more than .005 gap over a 4 to 5 inch span that's the limit most likey it's blown bbetween 2&3 get OEM Merc. stuff

 

[Bondo]

Re: Merc 3.0 Low Compression 2 & 3

I'll bet you a nickel that it's not a headgasket.

Ayuh,.... I'll take it,...

I'm with bafflefan,... I see a head recon. at Best....
Block, 'n/ or head damage at worst...
Course there could be manifold problem besides,... donno...

 

[tschmidty]

Re: Merc 3.0 Low Compression 2 & 3

Gotcha, and after thinking about it it will be best to pull the head and see where I am at before getting carried away. And yeah I'll pull the manifold too. I always dream of doing the job halfway to save money but I am old enough to know it doesn't actually save you money when you have to pull it apart and do it over right away.

Guessing the gasket failed from overheating considering the state of the impeller when I pulled it in the spring. Betting it caused either temporary or permanent head warpage. We'll see.

 

[Don S]

Re: Merc 3.0 Low Compression 2 & 3

Also check (with a straight edge) the narrow area of the head and block between cylinders 2 and 3. That area can erode away very quickly leaving a low spot that will not seal with a new gasket, and may be too deep to machine.

Can I get in on this free nickle thing too?

 

[TilliamWe]

Re: Merc 3.0 Low Compression 2 & 3

Can I get in on this free nickle thing too?

Nah, actually my bet is only with the original poster. Bond-o isn't getting one either.

I say that exhaust can/is the issue, is because he hasn't told us about any overheat or any other reason to believe a headgasket is blown, other than low compression on two adjacent cylinders. Yes, I know, in the auto world, blown headgasket is the number 1 thing to think of. But in the marine world, exhaust manifolds failing allowing water to rust those valves is a possibility. As is tulipped valves. It does't HAVE to be a headgasket or warped head issue. It very well could be, and I would then gladly give the original poster a nickel.

 

[Don S]

Re: Merc 3.0 Low Compression 2 & 3

The one thing I see in this forum, (not just this post) is that DIYers like to throw parts at a problem, no one ever wants to actually troubleshoot a problem and find out exacty what it needs, just throw parts at the problem. which usually means you fix what the real problem caused, but never found out what the problem actually was.
It's so easy to check for a blown head gasket by just pressurizing one cylinder and listening for air in the next spark plug hole. IF no air, then a head gasket probably won't cure the problem. But who wants to go to all the work by doing a leak down test when you just just throw a head gasket in and hope for the best. Then take it all apart again........... and again.................and again, until you happen on the problem.

 

[tschmidty]

Re: Merc 3.0 Low Compression 2 & 3

Yeah, but head gasket is cheaper than a leak down tester! OK, not all that different, but it really should be pretty clear what the issue is once the head is off.

Thanks for all the heads up. I definitely appreciate the advice you guys give out.

 

[stonyloam]

Re: Merc 3.0 Low Compression 2 & 3

1. Am I confident enough to just order a head gasket and rocker cover gasket and have at it? Ie, order those before I tear it apart

I think that would be unwise. Head gaskets (it sounds like one to me too) do not just fail. They fail for a reason. If you do not determine the underlying cause, you are just asking for more trouble. My suggestion would be to take it to a shop and have it checked out, including the valves. If you do it right this time you will not have to worry about it for a long time. Good luck.

 

[tschmidty]

Re: Merc 3.0 Low Compression 2 & 3

OK, the good: Exhaust manifold wasn't leaking.

The Bad: Definite head gasket failure with head and block damage. Do you think the big chunk of impeller stuck in the water passage contributed? </sarcasm>.

Here is the overall pic and you can see the blown out gasket.

Close up of the block, very similar damage to the head (a small crack down the center between the cylinders)

Here's a question, what is with the exhaust valve on the left "retracted into the head? Burnt I am guessing?

Opinions on fixing it? I know some will say the engine is done for but curious if there are any reasonable fixes to be had. Replacing the engine is not gonna happen for cost reasons (would look for another boat instead most likely).

 

[Bondo]

Re: Merc 3.0 Low Compression 2 & 3

I know some will say the engine is done for but

Ayuh,... No Buts to be found,.... Picture #2 tells the story.... That's a Dead Horse....

The sunken valve is seat failure, valve failure, or both...

You've pretty much got an Anchor,...

 

[TilliamWe]

Re: Merc 3.0 Low Compression 2 & 3

I'll give you your nickel the next time I see you, t. But you obviously left out overheat issues. Cause that is what the impeller blade was doing in there. The valve could be tulipped, due to the high heat in the combustion chamber.

 

[tschmidty]

Re: Merc 3.0 Low Compression 2 & 3

Thanks for all the advice. Kind of curious here, with the sunken valve, seat of the pants feel says the valve spring on that valve is weaker than on the other valves. Could that have contributed to the valve failure since the valve might have a tendency to float at higher rpms? Just not sure how likely that is. It's not like barely staying close kind of weak but certainly not as strong.

 

[coheej]

Re: Merc 3.0 Low Compression 2 & 3

The valve spring is definitely weaker now, but is not the cause of the seat failure. The spring should have been at normal strength when the failure started to happen.

 

[cr2k]

Re: Merc 3.0 Low Compression 2 & 3

If your block if flat and doesn't need to come out for machining you can replace the head and go.

The 3.0 engine is a great little engine. It DOES however need to be keep up with service wise.

Yes; not finding every piece of a failed impeller did very much contribute to this problem.

So many people take that little rubber star thingy sooo for-granted.

 

[coheej]

Re: Merc 3.0 Low Compression 2 & 3

I think he indicated the block was cracked also. The crank and rods may be good, but other than accessories everthing else is mostly junk.

 

[tschmidty]

Re: Merc 3.0 Low Compression 2 & 3

And yeah, the impeller bit me. A case of 'it ran fine on muffs' but overheated first time out. I didn't run it long myself (shut it down and paddled back to shore for an hour) but considering how bad the impeller was I wouldn't be surprised if the previous owner had overheated it before he sold it to the next sucker (me!).

After cleaning it up the two cracks are very small and neither looks like it extends past the surface. The head leveled out pretty well within spec (<0.004) but not sure about the block yet. From what I can see it doesn't extend into the cylinder walls. If the block will clean up OK, I will slap a gasket on and see how long I can get out of it. Considering that it's a case of tossing the motor if it blows, not really sure what I have to lose. The sunken valve is definitely a concern but again, worst case I blow the motor. The motor was actually still running well last time I was out, 38-39 mph 4300RPM 19P prop with 3 people on board so hoping I can get a little more time out of it.

Taking bets for how long until my inevitable post of 'Anyone know where to get a good used 3.0 motor?'

Question for the guys who actually know what they are doing, why are the water passages into the head restricted at the head gasket? If you look the passage is much bigger than the hole in the gasket which is where the impeller chunk lodged. You can see it laying next to the passage in the first picture.

 

[coheej]

Re: Merc 3.0 Low Compression 2 & 3

The head leveled out pretty well within spec (<0.004) but not sure about the block yet.

If you're .004" low in the middle between those two cylinders, you're wasting your time.


Question for the guys who actually know what they are doing, why are the water passages into the head restricted at the head gasket? If you look the passage is much bigger than the hole in the gasket which is where the impeller chunk lodged. You can see it laying next to the passage in the first picture.

The holes in the gasket controls the water flow in each area of the block and head for uniform cooling. If it didn't restrict the flow you would have hot & cold spots.