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Old April 7th, 2020, 07:27 AM   #1
Ryanw10
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Default Mercruiser head gaskets

Brought home a new to me chris craft on sunday for a great price. The previous owner said both motors run good, but the starboard side was always at a different RPM. Compression test revealed that the port side of the starboard motor is not doing so hot, and there was definitely a slight amount of water in at least 3 of the cylinders. Starboard side of the motor seemed good until my compression tester took a crap on the last cylinder. Going to get a working tester and get the compression in the last cylinder, and the question is, do I leave that side alone if the compression is 115 or more? Or since I'm going to have the other side apart pull both heads off. Oil is nice and clean on the dip stick, and if the meter is right, it has 650 hours.

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Old April 7th, 2020, 07:39 AM   #2
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Personally i would do both sides. Reason I say that is we don't know why the gasket is failing on the port side. Did the motor overheat? I wonder if an impeller or water pump went and the engine got too hot.

I would also check compression on the port side motor.
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Old April 7th, 2020, 10:58 AM   #3
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Personally i would do both sides. Reason I say that is we don't know why the gasket is failing on the port side. Did the motor overheat? I wonder if an impeller or water pump went and the engine got too hot.

I would also check compression on the port side motor.
This is what I would do for someone else or if being paid... personally I am a bit lazy and usually worried about the snowball effect that removing the second head would cause. What happens if you break studs taking off the water cooled exhaust etc. I would only do what is needed with my own stuff lol
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Old April 7th, 2020, 10:59 AM   #4
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......and working on boats sucks major balls and is a huge pain in the ass!!!
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Old April 7th, 2020, 12:13 PM   #5
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This is what I would do for someone else or if being paid... personally I am a bit lazy and usually worried about the snowball effect that removing the second head would cause. What happens if you break studs taking off the water cooled exhaust etc. I would only do what is needed with my own stuff lol

this, caveat being if you do the complete top end, you know that much is good to go. I would rather have ALL the valves sealing alike.

BONUS! When you find the cracked block the previous owner neglected to tell you about, you have a completed top end to go on that short block.


Is that a Stinger?

Last edited by XXXJ; April 7th, 2020 at 12:17 PM.
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Old April 7th, 2020, 01:55 PM   #6
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It's a 1980 26' scorpion. Not sure if I'm going to flip this or sell our liberator.

After tearing into it this morning I realized it was not that much more work to pull the other head. Lots of room to work in this engine compartment.

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Old April 7th, 2020, 01:58 PM   #7
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Cylinder #3 shown below. Head gasket seems ok? Dropping the heads off this afternoon to get checked

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Old April 7th, 2020, 02:03 PM   #8
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Can you guess what valve shown is cylinder #3??

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Old April 8th, 2020, 05:16 AM   #9
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Wow!
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Old April 8th, 2020, 09:04 AM   #10
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Awesome you have room to work and that's a pretty nasty looking cylinder!
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Old April 8th, 2020, 12:42 PM   #11
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I would take a wire wheel to the heads and pistons (in place), replace head gaskets, check compression, change the plugs and oil and fire it up. That outdrive prolly needs a impeller or water pump or both. I would just replace both impellers they are cheap insurance.
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Old April 8th, 2020, 03:52 PM   #12
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I would take a wire wheel to the heads and pistons (in place), replace head gaskets, check compression, change the plugs and oil and fire it up. That outdrive prolly needs a impeller or water pump or both. I would just replace both impellers they are cheap insurance.
Started wire wheeling with a brass wheel today on the block and pistons. First though I went through with a razor blade to get the big chunks. Machine shop just called and both heads will be getting a valve job and they will be supplying me with a top end gasket kit. I know both impellers were new at the beginning of last season

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Old April 9th, 2020, 06:58 AM   #13
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Ya may want to have your exhaust manifolds pressure tested too. Definitely check Gasket surfaces between manifold and riser for leaks as well. Be a shame to go through all the top end an find out it was a cracked manifold dumping water into it.
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Old April 9th, 2020, 07:19 AM   #14
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Ya may want to have your exhaust manifolds pressure tested too. Definitely check Gasket surfaces between manifold and riser for leaks as well. Be a shame to go through all the top end an find out it was a cracked manifold dumping water into it.
Excellent point!
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Old April 9th, 2020, 07:24 AM   #15
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Ya may want to have your exhaust manifolds pressure tested too. Definitely check Gasket surfaces between manifold and riser for leaks as well. Be a shame to go through all the top end an find out it was a cracked manifold dumping water into it.
That's next on the list. Valve seats according to the machine shop definitely needed to be done and based on my compression test I'm glad I'm going through the whole top end like this.

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Old April 10th, 2020, 12:02 AM   #16
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I will bet that the engine looks just like that side or there was a leak above the intake on just that side.
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Old April 10th, 2020, 01:58 PM   #17
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Made an interesting discovery today...

I took the risers off the manifolds and the gasket between them appears to be for a closed loop system where the motor is NOT taking on

Second picture is with the gasket on

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Old April 16th, 2020, 08:50 PM   #18
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I believe I was incorrect on the riser gaskets, they are supposed to be there.

The heads I dropped off at the machine shop ended up being cracked and severely pitted around the cylinder that was taking on water. They hooked me up with a different set and did a valve job and resurface on them. Was going to bring the manifold to them to pressure test until I discovered what I think was the root cause of all this. New manifold is on order.

Intake is cleaned and painted and the block and pistons are cleaned up. Going to start reassembly this weekend

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Old April 17th, 2020, 07:32 AM   #19
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awesome!
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Old April 17th, 2020, 10:05 AM   #20
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Looking forward to seeing your compression results after reassembly. And of course, videos of the fire up and the ride.
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