92 mariner 115 4 cylinder electrical problems and a soft knock in motor

[Tazs92mariner115]

I have a 92 115 mariner 4 cylinder. The boat sat for over a year without even running, then I ran it last fall. Winterized it and it sat through the winter. Now this summer, It's had this problem of not starting. It also has had erratic tach and volt readings. I attributed it to the circular main harness inside the motor cover. It would go to having nothing at all when you turn the key, to it turning over and having it not even try to start at all. When this is acting up I know because the tilt won't work on my stick shift to raise the motor. I've got a tilt switch on the front and back, and on the '**** pit' tilt on the shifter. When it's done this, I opened the cover and pull that loom apart and put it back together, everything worked again. WELL, now yesterday it sounded like the motor had a knock in it. It also continued to run for I'd say like 5 seconds after I turned the ignition to off. I inspected today took the spark plugs out and there was some flakey gray looking stuff stuck in one of the spark plugs. I pulled the cover on the back of the motor and as I am turning the flywheel by hand, I can hear a strange noise coming from the top of the lower unit. Could a carb problem be the cause? I'm going to take the left side of the motor apart too to look at the pistons. I'll report back but besides if I see a scored piston, what else could it be? What should I look for if there's a spun bearing? The knock I heard wasn't a loud knock but it was surely enough to get my attention. I originally thought oh electrical, like a cylinder was not firing, at all but what should I look for if it's more than just a cylinder not firing at all?

 

[Steven P.]

Re: 92 mariner 115 4 cylinder electrical problems and a soft knock in motor

Was the sound you heard a knock or a ticking sound. If you have to run it again and listen close. If you have a compression guage check compression and post what you come up with. Compression doesn't always tell whats going on. One thing to remember that motor doesn't run on all 4 cylinders till around 1800 rpm. Just top 2 up to 1800.

 

[Tazs92mariner115]

Re: 92 mariner 115 4 cylinder electrical problems and a soft knock in motor

I'm going to tear it down a little further before I try to start it again. I've never heard it make that noise any other time. Is there a bearing in between the power head and lower unit? The metal flaking I saw in the spark plug has got me wondering if it was nothing more than filings from replacing the spark plugs like two weeks ago? Was it just carbon that flaked off the piston? Carbon is black but would it turn gray after being burnt? The number three cylinder is where you can hear a slap when the spark plugs are out and I'm turning the flywheel by hand. I will also get a compression check as well before I tear it down any further. Right now I've just got the back cover off of it. I will report back with what I find. Thanks for the help!

 

[Tazs92mariner115]

Re: 92 mariner 115 4 cylinder electrical problems and a soft knock in motor

Oh yeah there is one thing that has not escaped the narrow part of my mind. A few years ago, I had a stud on the bottom of the powerhead and top of the lower unit snapped off, front right side. It's been that way forever. Well then this year I tightened a couple of smaller bolts that had worked loose in between the powerhead and lower unit. I'm wondering if that has something to do with it as well. I found the stud on the ground so it snapped with a crack then just fell off. The studs that have the nylock nuts on them, the front right one snapped but that was a few years ago though, maybe that is coming back to haunt me. Like I said though, compression check and then I'll report back with what I find.

 

[Tazs92mariner115]

Re: 92 mariner 115 4 cylinder electrical problems and a soft knock in motor

I found maybe a 6 psi difference in all the cylinders. Around and just over 105, so with that being checked, is it possible that the lower crank bearing went out and the knock was coming from the side of the piston in cylinder number three because of the slop in the lower crank bearing? It would explain the flaky grey like stuff that I pulled out of the number three spark plug. Thinking I should change the bearing and seal and maybe while I'm at it, get a rebuild kit for the impeller, but I know for a fact it was pumping water. If three got stressed from a carburetor issue with it running it lean, it would score the piston and there probably wouldn't be as much compression. Am I wrong for my speculation about the lower bearing going out and the whole crank finding new tolerances? The motor kept running after I turned it off for like 5 seconds... because of the crank being out of place?

 

[Tazs92mariner115]

Re: 92 mariner 115 4 cylinder electrical problems and a soft knock in motor

It was pumping water into cylinder three, and part of the gasket is what I found in the spark plug( the grey flaky metallic like pieces) the middle two pistons have oil line witness marks. There 's no score marks on the pistons. I'm still thinking the lower crank bearing went. There was sand in the induction plate and through out the layers. There was a stud that broke off like two years ago. It was the right front side stud I found laying on the ground. I never thought any more about it because there was no water in the lower unit grease when I changed it, So I left it alone. I'm thinking after the start up of this year, is when I noticed a few bolts in the front of the exhaust plate were loose and I just tightened them back up. I think the lower crank shaft bearing is the culprit. I will continue to report back on what else I find. I hope that new bearing lines the powerhead and the driveshaft housing up and I hope that slap will come back out of cylinder three. That is where the soft knock was coming from.

 

[Steven P.]

Re: 92 mariner 115 4 cylinder electrical problems and a soft knock in motor

The color of the spark plugs should be black or dark brown. If #3 is greyish in color then you are getting aluminum transfer from your piston and cylinder wall onto your spark plug. In this case you will have ok compression but the damage is to your piston skirt not so much to the rings. You would have to go in from the front removing carbs. and intake and get a scope lite to see in cylinder. I had a 60 mariner a few years ago with this problem.

 

[Tazs92mariner115]

Re: 92 mariner 115 4 cylinder electrical problems and a soft knock in motor

Yes I know that the induction plates had sand in it and the gasket was leaking in two places, middle cylinders. The grey flakes I found on the spark plug, had gasket DNA all over it. I will have to pull carbs and check the pistons and connecting rods out. If it trues up after I change the lower crank bearing, that will be half the battle. I might have gotten lucky with the crank and the rest, but I won't know till I pull the carbs.

 

[Tazs92mariner115]

Re: 92 mariner 115 4 cylinder electrical problems and a soft knock in motor

I have to get the flywheel off, and take the crankcase off, but it looks like the mechanical issue is with cylinder 4, I actually found a piece of smashed metal and it looks like it has some copper in it. I'm thinking it is either a piece of the connecting rod or the crank case housing. I won't know for sure till I get the crank and piston out. Unknown also if it is just a problem with cylinder four, or if it is in fact part of the lower bearing. I'm hoping the wear sleeve with the lower bearing is what caused the problem. I will also take some pictures and post them when I can. There was water getting into the crank housing because the second bearing in between 1 and 2 has a little surface rust on the race.