78 Johnson 115 low compression 1 cylinder

[Bosunsmate]

I was testing whether it was firing or not by pulling off the plug wires while running. Also, when you say, “Your cylinders are sounding pretty bad”, are you implying they should have much more compression, I’m assuming? Thanks!

Singularly not plural- i shouldnt of added an S to cylinder. Just the one cylinder isnt looking so hot.
But i agree with Harrington, 103PSI is more than enough to make it fire. I suggest you find out why it isnt before you tear it down.
Ive had motors work on low compression on one cylinder for a long time. The gouges get carbon in them and things can settle down for a long time. So if you are like me and every penny counts then thats what i would be doing, ideally you should be looking to rebuild but Macgyver wouldnt and he gets by

 

[Faztbullet]

ideally you should be looking to rebuild but Macgyver wouldnt and he gets by

MacGyver is a fantasy show...sort of like da free energy chit going around.

 

[Deuce24]

Fellas, thanks for all the help/advice! I’ll post some pix this weekend and keep y’all posted.

 

[racerone]

My guess it that the black mess is a result of the gasket leaking between the block and exhaust housing.-----Some think that this more will heal itself and run OK.----I have some of last week's lottery tickets at half price.

 

[Bosunsmate]

ideally you should be looking to rebuild but Macgyver wouldnt and he gets by

MacGyver is a fantasy show...sort of like da free energy chit going around.

:laugh:Well i did get my Four wheel Drive home from the back country once by doing something Macgvyer would
The alternator went and the battery was losing power, soon enough the fuel pump and solenoid would cut off.
So i used the graphite from a pencil to make the brushes and it worked enough to get me home. I sung the Macgvyer tune most of the way back.
When you dont have much money sometimes you have to do what can work even if not optimal

 

[Deuce24]

So I was able to pull the head cover off and here are the pix. I also did notice some water in the bottom cylinder and spark plug would not ignite when lit with a lighter.

 

[Deuce24]

Pix are of the top cylinder which has good compression, and 2 pics of bottom cylinder 1 is the top of the bottom cylinder and one is the bottom of the cylinder.

 

[racerone]

Picture is worth a 1000 words.

 

[Deuce24]

Picture is worth a 1000 words.

Where the discoloration is there aren’t actually gouges. There is a small gouge just to the right of the discoloration more like 6:30.. same on top of cylinder. The gouge on top is at 12:00. What is the discoloration from? Obviously something happened there but it’s as smooth as the rest of the cylinder.

 

[Deuce24]

So...resleeve, new piston and rings? If I’m going to take it apart to do one I’d just assume do em all. So the question is.. is that motor worth doing that to? I don’t mind spending the time to do it, but is it worth the $$??

 

[harringtondav]

So...resleeve, new piston and rings? If I’m going to take it apart to do one I’d just assume do em all. So the question is.. is that motor worth doing that to? I don’t mind spending the time to do it, but is it worth the $$??

Figure a new motor at $80-$100/hp. Consider unknown used motors are unknown, and maybe worse than what you own. Are you into boating for the long haul?

I can only offer things to consider for your decision. It's clear you have the ability to tear down and rebuild. Your big costs will be the machine shop, and new pistons. You need to gather these. This forum can steer you to a piston/ring supplier. I don't remember it. Your best bet is to contact a reliable auto machine shop and get a verbal estimate.

I've always considered 2 stroke O/Bs as very robust and long lived. If you're into boating for the long haul, a rebuild may work out.

 

[racerone]

Some will argue.-----It is also time to evaluate the lower unit.------Be a shame to invest coins into the powerhead and then find out you need gears and bearings too.----Motor is 40 years old and likely needs at least a seal kit and impeller.

 

[Faztbullet]

If its a virgin and never been into you will have to replace all 4 pistons due to high ring design. Don't need a sleeve just bore oversize. IMO not worth putting $1100 and time into a $750 motor.

 

[Bosunsmate]

Ok so you know why it wasnt firing. Have you worked out how the water was getting in?
Was it the head gasket or Exhaust?
I wouldnt spend money on it. Id give those cylinder walls a rub down with light wet sandpaper. Then solve the leak problem- you may just need to shave/sand the head on a piece of glass or a mirror with sandpaper on it as they get warped rather easily.
Drop the LU and attach a hose to the water pipe inlet into the engine. See how she runs on that. If ok then check over the LU especially the impeller, check the oil too and then go boating.
You may get a long time out of it and sure one cylinder may be down a bit on power. So you may lose 5% or so top speed but you also will have $1000 still in your hands

 

[jimmbo]

Id give those cylinder walls a rub down with light wet sandpaper.

ROFLAMO:rofl:

 

[Bosunsmate]

ROFLAMO:rofl:

Haha, i get the same reaction when people see the rest of my belongings

 

[interalian]

If you can do all but the machine work yourself, these old pigs can be worth the effort. But it's been said already: what's the condition of the gearcase?

I did a top end rebuild knowing (at the time) the gearcase was good. A year later I found the driveshaft has a plating failure which made it rust underneath and flake off, just where the water pump seal rides. I have a spare LU that's working OK but the skeg was beaten in its earlier life. I'm thinking about swapping its guts into my nicer housing.

racerone once promised he'd come help me do that work - maybe still?

 

[racerone]

The wee ones are coming to play in Ontario this summer.----Next year for a trip to the Sundre area for me.------Perhaps bring an an ---Action Marine 17---- with me.

 

[interalian]

Now that looks like it'd be fast. Where's water around Sundre? Glennifer, Sylvan, Gull, I guess.

 

[Deuce24]

Update.. replaced the head gasket and exhaust cover gasket. Still have good spark and still nothing on that bottom cylinder. All rings were in tact, was some blow by, and the bottom ring on the bottom cylinder in question was/is seized up, upper ring seemed ok. The oil running down the motor was definitely from exhaust cover gasket failure(and a little from carbs when tilted up). I was hoping I was getting water from this failed gasket as well, but still not sure that I was.