Merc 402 - Water Coming out near Cyl1 spark plug

[cambo]

My old MERC 402 suffered some fairly serious problems (splines on crankshaft and drive shaft bent/stripped). So, I picked a couple spare units up for parts. I got everything together and things seem to be in order. Changed gear oil, new impeller, new gaskets between powerhead and mid-section.

Model: Mercury 402 (2cyl, EL - Electric Start, Long-Shaft)
Serial Number: 7102322
Year: 1977

Here is the current setup:
Powerhead: (new to me motor #1 - everything except ignition)
Lower unit: (new to me motor #2)
Ignition: from existing motor (I know it was working)

Initial Tests
Compression: 120PSI on cyl1&cyl2
Spark: good - plug 1&2
Fuel: good

So I fired up the FrankenMERC 402 on the muffs and it started up and it seems to run good. Sounds good and has a good pee stream.


The problem I'm having is there is water coming out from below/around spark plug hole on cyl#1. What I gathered from previous threads indicates this is probably the gasket behind the cylinder block cover.

My question is: Is it possible to replace this gasket without tearing the whole motor apart (ie. without taking bottom end off, mid section, etc)? Any other options to fix this leak (JBweld, high temp silicone, other)? If it does require a gasket change, does this gasket require gasket sealer or would it go on dry?

Thanks,

-Cambo

 

[jmburock]

Re: Merc 402 - Water Coming out near Cyl1 spark plug

This is definitely a leaking water jacket gasket. The only acceptable fix would be to get a new gasket and put it in there. They go on dry although you may want to put some permatex around the spark plug cutouts as this is where the leaks begin. You don't need to take the whole motor apart to change this gasket, but you do need to deal with some of the most break-prone bolts I have ever encountered. I broke 8 out of 14 of them and spent quite a while drilling them out and putting in Heli-coils. Good luck.

 

[NJCinMN]

Re: Merc 402 - Water Coming out near Cyl1 spark plug

Not to dispute jmburock as he is suggesting the proper way to fix this issue but I've read several posts by reputable source on this forum to avoid taking the water jacket off at all costs because of the issue of broken bolts. They suggest time and time again to degrease and put a bead of silicone around the leaking cylinder first and then if that doesn't work you're on to the "proper" fix. Of course this only applies if you have a minor leak. If water is gushing out then you must remove the water jacket and replace the gasket. Good luck.

 

[jmburock]

Re: Merc 402 - Water Coming out near Cyl1 spark plug

It is indeed a difficult job to deal with these bolts. Hopefully your motor isn't run in all saltwater like mine was. Certainly worth trying to silicone it first. Test getting one bolt out and if it gives you any trouble consider stopping until you are prepared to drill out hardened 8.8 bolts and put in Heli Coils. I can assure you that you will go through multiple cobalt tipped drill bits if you have to drill them out...

 

[NJCinMN]

Re: Merc 402 - Water Coming out near Cyl1 spark plug

One other thought...some older mercs had nuts on the back side of those bolts instead of turning into the block. If that's the case then no worries about breaking bolts other than needing to buy new nuts and bolts.

 

[cambo]

Re: Merc 402 - Water Coming out near Cyl1 spark plug

This particular Merc had the nuts on the backside (not threaded thru the block). In any event, I had to remove the head to get the bottom bolt out (nut was spinning). Just as well, since it would have been pretty well impossible to remove the old gasket and torque the bolts properly with the bottom cowling in the way.

For future reference, does anyone have any efficient methods for removing old gaskets. I just took my time with a razor blade and it seemed to work (then used a soft plastic scouring pad to clean it up), but I imagine there is a much better way?

I haven't tested it on the muffs yet, we'll see how this new gasket holds up.


Thanks,

-Cambo

 

[cambo]

Re: Merc 402 - Water Coming out near Cyl1 spark plug

Tested the motor out tonight on the muffs. Unfortunately, even after changing the gasket there is still a small leak below spark plug #1 (although, much less than before - what was a weak trickle is now a slow drip). Not sure what I did wrong here, is it possible the cover is warped?

Basically, I cleaned off the old surfaces good. Installed a new gasket, using a thin coat of Permatex? Aviation Form-A-Gasket? No. 3 Sealant. I then tightened the new bolts in three passes (25in lbs, 50in lbs, then 70in lbs), in the bolt order specified in the Seloc manual. The gasket isn't leaking anywhere but below spark plug #1 (exactly the same place as before I changed it).

Any ideas what happened here? I think I'm going to try the high temp silicone around the leak area.


Thanks,

-Cambo