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87 merc leaking water from next to top plug

M

Mugsydigs

New member
My 87 45hp 2 stroke merc mariner is leaking water from a small hole just beside the top spark plug. Consequently soaking the other plugs causing misfire. Is this a water jacket? Worth fixing? Any advice would be helpful, thanks!!!
 
Yes, the water jacket - could be just the gasket unless you have (burned/rotted) a hole in the cover itself (salt will do this over time).

27-437772 is the merc part number for the gasket, runs about 11 or 12 bucks - worth trying...
 
On replacing this gasket in particular, I like to use an adhesive. Reason is that corrosion is usually present and the pits interfere with the seal functioning properly. So I clean off the corrosion, use something like Disc Brake Spray Cleaner to cleanse the surface, apply Blue RTV Adhesive and button her up.

Normally the water jacket cover bolts are corroded and like to break off on you. A good pre soaking with a good penetrating oil (PB Blaster for one) helps. Then I like to use impact and that can be as simple as a box end wrench on the head of the bolt and hammer whacks on the end of the wrench. Once you get it moving you are usually OK. It's the breaking loose that is the gotcha And whacks work where a constant twisting force will/can just twist off the shank....usually down in the block where you can't get to it to remove it!

With the bolts out, wire brush the threads and run a suitable tap in the block holes. If you will apply Blue Locktite thread sealant to the threads prior to insertion they will go in easier and will be less susceptible to corroding and making future removal easier. All these chemicals are at most auto parts stores.

Mark
 
Agreed. Just did a Merc 110 with a new gasket--and it leaked like a sieve. Added silicone to the gasket and it worked fine.

Jeff
 
Awesome complete informative responses as usual you guys. I've been watching this thread because it looks as though I have this same problem on the 87' 25 HP I've been working on. I'll need to fix it once I get the carb right. Thanks. Rob
 
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