1984 Johnson 115 Spark issues

[Scovbert]

Hi all, It seems I’m only getting spark on the top 2 cylinders, the other 2 that don’t seem to spark are on different banks, which seems weird to me because most of the time if 2 cylinders drop out it’s on the same bank. I’ve done all the basic diagnostic checks. Stator looks good physically and ohms out as it should. All 4 coils ohm out good. Both power packs are good, I just replaced one that was bad, Regulator/rectifier is brand new. I’ve replaced all 4 plug wires and put in brand new plugs gapped to the manual specs. I noticed while running at idle on muffs the motor would stall, but would sound like it was running great at 1800-2000 rpm but still would occasionally miss. My spark tester shows spark on all 4 but it just can’t be possible. I pulled all 4 plugs and all 4 were wet but the top 2 showed signs of ignition and the bottom 2 looked brand new still, just wet. I rebuilt the carbs prior to all this and it’s running on fresh gas. I did a compression test and all 4 cylinders read 110psi even. All grounds are good and clean. I’m leaning towards the timer base, but I’m not a 100%. Any advice is appreciated.

 

[Bosunsmate]

test the wetness with a lighter, it may be water.

 

[Scovbert]

So just to clarify, it turns out my spark tester isn’t lying, I pulled all 4 plugs I checked them against the block. All 4 had bright blue spark so it’s not a spark issue after all. I’ll confirm it’s not water now and report back. Just out of curiosity how would water get in the cylinder?

 

[Scovbert]

Smells like a hint of gas but would not light when I put a match to it.

 

[Bosunsmate]

Youve water mixing in it then, id suspect exhaust gasket first

 

[Bosunsmate]

And you need to get it done without delay as water in those bearings will be forming corrosion soon, so spray wd40 or something similar in there as soon as you get the exhaust cover off. If there are inlet covers on that itd be worth taking them off for the bottom two cylinders and spraying in there too.
You can also drop the LU and run it for about twenty seconds to lube it up

 

[Scovbert]

Pulling it apart tonight, hopefully just the gasket! Thanks for all the advice, I’ll get penetrating oil in there ASAP. I’ll report back.

 

[Bosunsmate]

If you can, you really want to get it in behind the piston too where the bearings are. Turning the motor over by hand to make sure moisture doesnt sit in one spot also helps

 

[Bosunsmate]

Have a look for the difference between the two pistons/ cylinders on top and the bottom when you get the covers off. Water ingress will make the pistons looks very clean, like they are steam cleaned. Sometimes just looking in the spark plug holes with a torch will show this.

 

[Scovbert]

I’ve looked in there with a light and the bottom ones are so clean I can read the numbers on the top of the piston. I’ll check the tops now. I was told by the previous owner that the motor was recently rebuilt but I thought man after a season there would be some carbon buildup. Now it makes sense.

 

[Scovbert]

I was able to get the cover and exhaust plate off, but it was a dreadful job without pulling the power head! I’m almost considering pulling the power head anyway because I don’t think I’ll be able to get the lower bolts back in. Anyway, as you assumed there was a very small amount of water in the bottom 2 cylinders and the gasket for the plate was completely shot. I added some penetrating oil to the cylinders anywhere I could get some. Tomorrow I will clean up both sealing surfaces and pick up new gaskets. I was considering doing the head gaskets and thermostats while I’m this far in but maybe that’s excessive. Thoughts?

 

[Bosunsmate]

Yep, i dont think ive heard anyone enjoy that job. Some people just drill through the back plastic lower cowling to deal with those bolts and put rubber stoppers in them afterwards. Id do that if i owned one, it looks quite alright to me but im not the type to wax a car.
You could clean out the thermostat housing. I always dril the little hole in the middle about double its current size, because if that gets blocked the engine can overheat then seize etc.
I wouldnt bother with the headgaskets at this point unless you dont mind spending the money. Its odd that back gasket has gone even though its just being recently rebuilt. Maybe someone was practicing doing a rebuild on it. You should check using a straight edge that the back plate isnt warped too much that the gasket wont work

 

[Scovbert]

Thank you for all your help! I’m going to the supply house soon to grab the materials for the job. Any recommendations on what gasket sealer to use? And should I use the breakable locktite on the bolts when reinstalling? I’ll look into the idea of drilling holes for the lower bolts, otherwise I’m not sure how I’ll torque them. I was fortunate enough to get them out using a universal adapter on a 6” extension and a deep socket, but it wasn’t fun.

 

[Bosunsmate]

No worries, im glad that you will get it fixed yourself. Here in NZ boat mechanics are very expensive.
i wouldnt use locktite on those bolts myself, ive never had them back out. Its being a while since i rebuilt a motor, mine are all going well touch wood, the only bolts ive normally used locktite on are the big end bearing bolts if ive being too tight to buy new bolts.
As for sealer ive always used permatex aviation form a gasket (i just like it because it sounds like it is used on aeroplanes) im sure most would do the job except cheap silicon ones. Just as a reminder, im sure you know, but do ensure both surfaces are clean of any old gunk as its quite some pressure that gasket has to contain

 

[Scovbert]

Thank you! So I bought the high end permatex and got the gasket for the exhaust manifold but they didn’t have the cover gasket in stock. They ordered that for me so it’ll be in tomorrow. Tonight I’ll clean everything up and get the manifold on and finish up everything else tomorrow. I’ll report back later or tomorrow with an update.

 

[Scovbert]

So it rained here the last 2 days but I was able to get all the materials I needed and clean all the sealing surfaces. I plan to go out there tonight and get the thermostats all done while I’m at it. They sold a kit for 32$ so I figured while I can access it all I might as well. Planning on wrapping this thing up tomorrow and trying it out. I’ll report back.

 

[Scovbert]

Just opened up the t stat housing and guess what? No thermostats were in there! Just the poppet valves. Glad I decided to look into this.

 

[Bosunsmate]

Thats a good find, starting your motor will be a whole better experience now. And you probably saved it from eventual cold seizure too.
Always takes a while to uncover what past owners have being up too. Ive just yesterday found such bad mechanics on my car, often im not sure if its the owner or a bad mechanic

 

[Scovbert]

Ok, so unfortunately this didn’t fix my problem completely. It seems as though the leaking into the port side cylinder is resolved or at least mostly resolved as the plug now shows signs of ignition. The starboard side is still not firing and still wet. So I can do one of two things. Throw this thing in the dumpster or try to change the head gaskets and hope that’s the problem. Very frustrated, any advice is appreciated.

 

[racerone]

Drop it off at my shop.-----Probably an easy fix.--------Does spark jump a gap of 7/16" ( 1 cm ) on all 4 leads , yes or no ?