1985 Johnson Lost power and died.

[Birddog1148]

Picked up this used boat, motor and trailer last fall. The engine is a '85 25hp Johnson electric start. Last fall I took it out once and it ran fine but the bow was way up. Last weekend I put a Hydro-fin on the cavitation plate. Took it out today and it ran fine for a few minutes then lost power and died. Smoke came out from under the cover and I heared sizzling. She cranks over fine but no fire, did get a couple backfires but that is it. Took it back to the shop and put the compression tester on it and both cylinders read 28 psi. When I put some oil in the cylinders the compression check bumps up to 30 PSI. That's as far as I have gotten. I read on an old post on here about a similar situation. I suspect the over the winter my water pump went bad and it overheated, head gasket maybe? Nothing looks unusual under the cover and when it cranks it could not see or feel any leaks.

 

[Solittle]

Re: 1985 Johnson Lost power and died.

Pull the head and have a look see. I suspect you blew the head gasket from the overheating. Not a big deal if that is all it is. Always a good idea to replace the water pump when buying a used engine.

 

[Bosunsmate]

Re: 1985 Johnson Lost power and died.

yes i agree with what you think there.
Take the head off, hopefully just a blown gasket

 

[Bosunsmate]

Re: 1985 Johnson Lost power and died.

Also, check the engine tilts all the way down as if a long pin is still in the transom mount area where all the holes are to adjust tilt setting it will keep the bow higher than it should be

 

[Birddog1148]

Re: 1985 Johnson Lost power and died.

Also, check the engine tilts all the way down as if a long pin is still in the transom mount area where all the holes are to adjust tilt setting it will keep the bow higher than it should be

Thanks for the quick replies.
It worked great with the fin, for the few minutes that it ran.
I'll try to pull the head this week and see what I can find. And drop the lower unit and see what that looks like as well. Figures, just as I am almost done getting the Baja Bug back roadworth this happens to take my time! :mad-new:

 

[Birddog1148]

Re: 1985 Johnson Lost power and died.

Ok, figured I would just sit around and waste time this afternoon so I went back to the shop to work on the boat. I figured I could get the head off without taking the whole thing apart but those bottom 2 bolts were to prove tough. But I got the idea to find a Tiawan socket in one of my junk boxes and make a tool to get in to those bottom 2 bolts. Weld a 3/8 nut on the back.


That did the trick. I will probably dress the spot welds a bit and shorten it up some but it worked.
The head came off and here are the pics:


One side of the gasket is a different shade than the other if you can see it.

Was glad there were no holes in the pistons

 

[Birddog1148]

Re: 1985 Johnson Lost power and died.

Now down around the impeller area. I cant get the shifter linkage disconnected from the top, need to do some wore looking but I pulled the 6 bolts out of the housing and got it apart that way. Housing looks damaged and some sleeve on the shaft is melted.



I know I will have to get that shifter linkage off to change the impeller housing.

 

[Bosunsmate]

Re: 1985 Johnson Lost power and died.

Your head look ok,
no scratches or dings indicating ring/bearing damage on the pistons that i could see
. Do the cylinder walls look smooth, no gouges?
Cylinder looks like its burnt through between cylinders

 

[Bosunsmate]

Re: 1985 Johnson Lost power and died.

I had an 83 a while back. If you post a zoomed out photo i might be able ot recall how to get that impeller housing off.
Thats a good tool you made there

 

[Birddog1148]

Re: 1985 Johnson Lost power and died.

Cylinder walls looked good and smooth, I doubt there is any damage in there. My thought was that the gasket failed between the cylinders as well. I will get another pic up when I can get back to the shop to work on it. Ordered a new gasket impeller kit with housing and spacer ( I figured that is what the melted mess is). Will need to change the lower unit oil while I am at it. And cant forget I dropped a 5/16 socket down in the lower unit. (I can see i looking in from the prop)

 

[Bosunsmate]

Re: 1985 Johnson Lost power and died.

Yes get that socket out of there, nice to keep a socket set together.

You must check the head for warping since you have it off and its had an overheat. It will leak straightawy if its warped. The good news is that its very easy to check for warping with a straight edge and its also easy to fix.
If its warped just put some light sandpaper on a plane of glass and move the head over it in a figure 8 pattern until all the head surfaces are shiny. The high areas will come up shiny first.

Its worth the effort as a warped head can quickly lead to another overheat if combustion gases pressurise the water jacket

 

[Birddog1148]

Parts came in a week or so ago and I finally had some time to work on it. The head must have warped a little because when I put a sheet of sandpaper on a piece of glass and ran the head back and forth on it only sanded the ends. This is where it is now.

Still a little dark between the cylinders but just a little. Should I sand more or is this enough?