'76 Johnson 6 hp; water leak into cyl from exhaust side ?

[BF]

Hiya,

Long time since my last post... I'm finally thinking I should get around to fixin' up my ole 6 hp... as per subject line it's a 1976, been in the family since new. I took it out of commission 2 years ago... it idles fine, compression is good, ignition is good... but at 1/2 throttle and above, it only runs on the upper cylinder, and the lower plug has water droplets on it after running above 1/2 throttle. Thinking it might be a leaky head gasket, I replaced that, but it was not the problem. The other suggestion made to me way back when was that it could be a leaking exhaust gasket, under the block-side exhaust cover letting water in to the bottom jug that way. I do have the factory service manual, but there are no instructions for R/R that cover or gasket. As far as I remember, what I should do is pull of that rectangular cover held on to the port side of the motor by slotted machine screws, inspect, and possibly replace whatever gasket is under there... sound right?

Here are some Q's:

I guess the power head needs to come off for this? Seems like it would be a nearly impossible job otherwise. There wouldn't be enough room to get an impact driver or screw driver on the lower screws.

If the power head needs to come off, I guess I'd also need a new exhaust gasket (if that's what it's called?), the sits below the motor. I haven't looked lately, but I guess the factory manual should have a section on powerhead removal.

Do the symptoms I'm having fit with a leaky gasket under the exhaust cover under the motor? I think (?) the problems may have started following an impeller replacement. It pumped WAY more water afterwards, so I'm thinking the water pressure throughout the motor likely went up quite a bit.

Would be nice to get this working well again... it's a nice little pusher for the next generation of kids to learn on.

Thanks for your $.02

 

[Rick.]

Re: '76 Johnson 6 hp; water leak into cyl from exhaust side ?

I've never worked on a 6HP yet so be careful listening to what I say. My first step would be to try my best to tighten up the screw/bolts on the exhaust cover as best I can. Only after that would I look at pulling the power head. It has worked for me on a 9.9 before. Best of luck. Rick.

 

[the machinist]

Re: '76 Johnson 6 hp; water leak into cyl from exhaust side ?

As you have noticed on the service manual for that motor if does not mention anything about the sideplate cover. As for taking it off, good luck without removing the powerhead as you have observed, as most I have seen will have at least one seized screw & that will always be near the bottom where it is hard to get a good grip unless you pull the powerhead. Plus on most I have seen, if it has any leaks in this area, it will usually be out as compared to having engine pressure inside.

When you replaced the head gasket, did you lap the head on a sheet of glass using valve grinding compound? Just in case the head was warped.

Your miss /dead cylinder could be in your electrical system. And with that vintage, your uses points & condensers. You could have a weak coil or condenser. Have you checked any of the connections under the flywheel.

Yes, if you pull the powerhead you would need that powerhead to exhaust housing gasket if that is what is is called on this model.

 

[BF]

Re: '76 Johnson 6 hp; water leak into cyl from exhaust side ?

thanks for the input... there are no outward leaks anywhere from the side plate cover. It's a low hours strictly freshwater motor and I know for a fact neither the power head or side cover have ever been off before. The ignition is good, I redid that a few years back with new parts when I first noticed some power loss. As for the head, I didn't lap it, but I did check it for flatness, and it appeared to be fine... I could tell the old gasket was original, and appeared to have no leaks, but it was replaced with the newer style gasket. Compression is good and dead even between the two jugs. The problem is a spritz of water somehow getting in there and quenching the fire on the lower cylinder.... not much... but enough. A leak coming in from the exhaust side does make sense, so I think that's the direction to go. Power head removal and then some careful impact driving on those screws is the prescription I guess. Ugh, I hope they come out better than I expect them to.

I found a exploded diagram of the motor, so I have a better idea of what's under that cover now... a plate & 2 gaskets... aside from pulling the power head off and getting out a bunch of 35 year old machine screws, it should be a piece of cake.

By the way, are you the same "Machinist" who posted the 9.9/15 hp maintenance article? If so, MANY thanks! I also have an '82 15 hp and that article has been of great help.

 

[BF]

Re: '76 Johnson 6 hp; water leak into cyl from exhaust side ?

an update just in case anyone ever turns this thread up on a search...

I finally got around to pulling the power head and changing out the exhaust cover gaskets... It went very smoothly. Pulling the power head was no problem. Once off, the rectangular exhaust cover (held on by 11 slotted screws) came off easily. No need for using an impact driver, they backed out nicely with a regular screw driver. Inside, there wasn't really lots of evidence of water intrusion into the exhaust chamber, but there were a couple spots on the bottom with the gasket was heavily caked with carbon. I'm hoping that meant that might've been the prob... carbon buildup could heated up the gasket and plate to allow a small leak into the exhaust side under high rpm's (=high water pressure). Reassembly was fine... I put a thin layer of permatec gasket sealer on the exhaust cover gaskets, and coated the threads of the machine screws with Merc "perfect seal" to keep them from corroding. I also replaced the exhaust gasket the sits under the power head. That one I left dry since it was pretty thick gasket, and I thought permatek sealant would just make a pain to get the power head loose if it needed to come off again.

I'll test run it this weekend and see if this solved the issue. The kids are stoked since they know this is the engine they'll get to learn on.

that's the update... just goes to show it is possible to get those covers off without a problem!

 

[Rick.]

Re: '76 Johnson 6 hp; water leak into cyl from exhaust side ?

Let us know how it runs on the water. I hope all is well. Rick.

 

[BF]

Re: '76 Johnson 6 hp; water leak into cyl from exhaust side ?

Last update:

Tested it on the lake today... ran stronger it but still didn't seem 100%... so I pulled the cowl off and did some diagnosing... if I partially covered the carb opening with my thumb, it picked up at WOT. So, diagnosis was it was running too lean. Thought it could be dirty carb (but I didn't think so b/c I had cleaned it not too long ago), maybe weak fuel pump, but pumping primer didn't help... disconnecting the fuel line while running WOT caused the engine to die < 5 seconds... that seemed too quick to be normal, so my guess was that the float level was set too low.


So, I went back to the cabin, pulled the carb... checked and it was clean... tweaked the float to ride higher and re-assembled. Ran great after that. Took kids for a 1/2 hour ride... didn't hiccup at all. On a 16' tinny with 1 adult and 3 kids, the 6 kept us planing (barely), but that seems about right I think.

The carb wasn't the major issue... there was a spritz of water getting into the lower jug and with it running only on the upper cylinder, just until I fixed the water issue, I couldn't tell the float level was off...

All 3 kids took a turn driving it lots of smiles... and all 3 (youngest is 9) could pull start it when it was warm. So, I'm guessing next summer this motor's gonna get a workout!

End of story!

Thx all.

 

[Daviet]

Re: '76 Johnson 6 hp; water leak into cyl from exhaust side ?

Glad you found your problem, sounds like the kids are glad to.