WATER JACKET/HEAD GASKET 1987 25 HP 2 STROKE MERCURY

[smokeysailor]

I just bought this motor, had it out 2 times. The last time it had only been running for 2 minutes hadn't even left the dock when water starting coming out one of the spark plugs! Do all failures of this gasket mean the engine overheated? or can it just be because of age? I am going to do the replacement myself, is there any tips to try and prevent the bolts from breaking? Any other advice , I would appreciate!

 

[flyingscott]

No head gasket on that motor. what is the compression? If compression is good resurface the water jacket and reinstall with new gasket?

 

[smokeysailor]

I will check the compression tonight.

 

[jimmbo]

The Water Jacket Covers on a lot of Mercurys will leak around the Spark Plugs, and yes it can happen because the Engine was starved of water, and the Cover would distort, and the Gasket would shift/tear.
Happened a Few Times on my inline 6, After the 3 time, the Dealer GAVE me a New Jacket Cover.
You could use some RTV and hopefully it will solve the Issue
More would be learned if you removed the Exhaust Cover, and looked at the Piston Skirts via the Exhaust Ports(that side of the Piston will show Scuffing before the Intake side

 

[smokeysailor]

The Water Jacket Covers on a lot of Mercurys will leak around the Spark Plugs, and yes it can happen because the Engine was starved of water, and the Cover would distort, and the Gasket would shift/tear.
Happened a Few Times on my inline 6, After the 3 time, the Dealer GAVE me a New Jacket Cover.
You could use some RTV and hopefully it will solve the Issue
More would be learned if you removed the Exhaust Cover, and looked at the Piston Skirts via the Exhaust Ports(that side of the Piston will show Scuffing before the Intake side

I checked the compression: The lower 83.0 The upper 88.5
85.0 87.5
89.5 86.5
I pulled 5 times and then read and repeated 3x's. I don't know how accurate a digital reader is? It seems like the better I pull the higher the reading. I am nervous about taking the jacket off. It has only been in lake & river water but I don't own an impact drill. It would really suck if I broke a bolt. I do all my maintenance and repairs. I don't trust the 2 boat shops in town, so I just google whatever I need to do. I am pretty handy. I put a deck on my boat, a floor, made a bench back seat and put a name on it and painted it. I want to install an electric start on the motor, so I can start it from where I sit instead of having to get up to start it. Do I have to take the jacket off to seal it up or can I just apply it around the spark plug?

 

[jimmbo]

You have to take the Cover off to replace the Gasket.
Here is when I did my 115

 

[racerone]

You should remove bypass covers to inspect pistons / rings.-----Do not spend any $$$ on this motor until you deal with the low compression.

 

[smokeysailor]

My readings are considered low? Great!

 

[jimmbo]

Quite low. As the numbers are Similar, You might want to try another Compression Gauge. When doing the Test, keep pulling until the Gauge reads no higher. Might take 3 or 4 pulls, might take 8 or 9... If the Rings are Stuck a bit of Combustion Chamber Cleaner overnight might help. I had suggested pulling the Exhaust Cover to view the Rings and Skirts, Racer suggested the Bypass Covers, on the Inlet, to do the Same. While the Exhaust Side will reveal Scuffing/Scoring earlier, if the Inlet side is damaged, the Exhaust will be worse. Pulling a cover will allow you to check for stuck or Broken Rings. The Bypass Cover is easier to remove

 

[flyingscott]

get a different gauge