water intrusion 1979 Merc 115

**fatlenny** · 06-20-2023, 05:40 AM

I am getting water intrusion in number 2 cylinder. Where would it be coming from?

Here is a little info.

I purchased a 1979 1/2 Merc 115 outboard for my project boat. She ran really good. never took her over 5500 rpm and always pissing strong, but I didn't have a temp gauge working at the time, normally playing around 4 to 5 thousand rpms.

I got a a deal on a 22 pitch SS prop on market place and got 50mph out of her at 5k rpms on Saturday. I tried to raise the motor up another half an inch and noticed it was not pissing as strong so I lowered it back down and quit trying to go faster at that time. Sunday I put the 15 pitch prop on it, lowered the motor way down, and went to the lake to play with some family and friends pulling a small tube. Temp sending unit installed and never got hot on Sunday..

I did have a hard time starting her at the dock and a fellow boater gave me a shot of ether and she fired up and seemed to run good. Took a warm up lap nice and easy around the lake, beached the boat and met up with my friends. we discussed getting the small tube and letting the kids play on a tube for a while so I let the graduate drive the boat back to the dock. her first time driving any boat. she did great. No issues, started right up, ran pretty good, but idle in gear was a little bit rough. I was thinking it maybe needed a little carb tuning, no biggy.

Got the tubes and started to play. The motor started to run a little rougher at idle, seemed to be smoking a bit more and running a bit rough. smelled like maybe a little rich. stalled a few times in gear at idle, but ran and pulled the tube with no issues after I put it in neutral and revved her up a little bit, seemed to clean it out and ran better.

I just wanted to give some back story to my issue so to my point now. Monday I pulled the boat out of the garage and figured I would see if I can get her to idle better adjusting the carbs a little bit. While I was filling up the 55gal barrel with water, I figured I would pull, check, and clean the plugs. number 2 plug had a milky sludge on it. I believe I understand these motors dont have heads or head gaskets.

I did sit down and try to do some research on my own and was surprised to find there is not really a head or head gasket on these motors to fail if I am looking at this right. I thought for sure that the cover was the head. I have worked on many small engines, but very little on Mercs. mostly air cooled, lawn mower, dirt bikes, or ATVs. Hoping there is just a failure on the exhaust side gaskets allowing water in on the downstroke from this side. Previous owner claims these gaskets were just replaced by a mechanic. It does look like new gaskets from the outside. I did notice one of the lower bolts loose a week ago and weeping a bit of water, so I tightened that one bolt and didnt think of it again till now.

I went back out and finished cleaning all the plugs and did a compression test. Numbers below. Put her back together and fired her up in a 55 gal barrel of water to do a little tuning on the air mixture screws on the carbs. Got her to smooth out and idle a bit better. I didnt take a pic of the plug the first time I pulled it but here is a picture of number 2 after running for about 10 to 15 minutes. I dont like the looks of this, and fearing the worst, but keeping my fingers crossed.

Click image for larger version.

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Compression numbers.
1-115
2-120
3,4,5-125
6-120

What is the bad news here?
Did I hurt this motor some time?
Where do I look for damage?

Planning on maybe pulling the exhaust side apart today, but will first just check for loose bolts on this side. If I find loose bolts I may just snug them all up on this side, pray, and run again in the bucket of water. I hope to hear from some people with lots of experience with these old inline Mercs and can give some insight.

**ChrisCarsonMarine** · 06-20-2023, 06:02 AM

Most likely a leak on the inner exhaust baffel plate,the one right over the exhaust ports.I don't think it's available new and takes special treatment to be reused,give a call,305-394-3354,Chris

**25two.stroke** · 06-20-2023, 11:11 AM

Originally Posted by ChrisCarsonMarine

Most likely a leak on the inner exhaust baffel plate,the one right over the exhaust ports.I don't think it's available new and takes special treatment to be reused,give a call,305-394-3354,Chris

He's right.
Pain in the ASS to fix. Especially salty motors...all the exhaust cover bolts wanna break. The inner baffle/water jacket cover is actually still available from merc @ $225. The outer baffle and outer cover are the ones that are nla...and at such a big span and likelihood to warp they are just as tricky. Did one on an 85 mariner 115 last year. I fixed it but it was not worth the time. Probably $1200+ in shop time from start to finish...and theres no way to bill someone that much for fixin a $1000 motor lol. Not to mention the epoxy mercury made to install those bolts with they don't make anymore, and the 20 yr old stuff we had here was no good anymore...

If Chris is willing to help you out on this one take him up on it...there are not many left who will do that for you!

**fatlenny** · 07-07-2023, 08:27 PM

Ok good news / bad news.

Been working on the merc 800 just so I can keep the boat on the water. Have plans the end of the month to take the boat up to the family reunion to take the kids out and play. So the 800 is working well. Water pressure seems low. connected the water line to the middle back port at the top of the jugs, cylinder block cover, ( showing only 8 to 10 psi ) witch I believe may be the wrong placement. Should water pressure pickup point be instead hooked up at the lower portion of the exhaust manifold cover? I purchased a new impeller, but current one seems to be pissing fine all the time.

Ok now back to the 115.

Good news.
Got her torn apart. Everything came apart pretty easy. Previous owner replaced gaskets 2 years ago. after talking to him I found that he used ant seize on the inner exhaust plate bolts instead of the epoxy or red loctite. Everything came apart pretty easy, but everything seemed still snug. Found that the gasket walked or squeezed out a bit on number 4 and looked the same on number 2, while number 2 ended up failing fully where number 4 looked like it was about to give our. So no cracks and I found where the water was coming from! YAAAAAA!

Now the bad news.
This leads me to my own dilemma on what to do next. number 1 piston has some pretty good scoring, ring shows score as well. ring may be pinched in the piston in this spot. surprised I still have 115psi compression. but this explains the lower compression in this cylinder. little bit of scoring in number 2. 3 and 4 looked good on the exhaust side, to be honest I didnt even look at 5 and 6. I may want to look at 6 as it was another cylinder that was a little bit lower on the compression side.

Now the motor is tore down this far. What to do?
Options
1, get a gasket kit for the exhaust, put it all back together and run it.
2, get a gasket kit for the exhaust, put it all back together and sell it, then look for another motor.
3, Get an entire gasket kit, needed pistons and rings (if available) Hone or bore, then keep and run it.

I already have $1500 in it. I would be leaning toward options 2 or 3 as I would be upset if I just ran it and it destroyed itself soon. What do you all think?

**Dave S** · 07-08-2023, 11:27 AM

3 1.....THEN GO HAVE FUNN....#2.... NO RESALE VALUE....# 3 BEING A 1979 SMALL PORT MOTOR....NA.....sorry I didn't know the caps were on.....

**derekfl** · 07-08-2023, 05:41 PM

from what i hear you can unbolt the rods and pull the crank just like the other merc inline motors. makes dealing with 1 recalcitrant hole less daunting.

**fatlenny** · 07-08-2023, 08:21 PM

Originally Posted by Dave S

3 BEING A 1979 SMALL PORT MOTOR....NA.....sorry I didn't know the caps were on.....

Piston and rings are not available to purchase?

**fatlenny** · 07-08-2023, 08:22 PM

Brought a pic for ya all.

Top piston (Right one in photo) has quite the gouge. Picture makes it look way larger than looking at it by eye. but maybe thats because I dont have my readers on my face when im looking at it in the garage. Number 2 has some gouging and looks like a brass color on the skirt when rotating the motor to see it. The other pistons look pretty darn good from what I can see through the exhaust ports.