Did i destroy my 1981 Johnson 35HP Seahorse?

[Ihateclevernames]

Gents, first time poster.............long time lurker. A good amount of information has come from this site in the past and I hope to gain more insight from some of you "old salty" dogs out there.

I recently purchased a larger modified V-Hull Alumacraft Jon Boat with casting decks and the works. the engine was a 1981 Johnson 35HP Sea Horse with electric start. the motor started up fine upon inspection and we took it out on the water, with a few choke issues, but once we got it going..........it ran pretty strong and smooth with the throttle more open than not.
The next day, I hooked it up to the muffs and started tinkering with the carb a bit just to ensure that things were clean and what not. Upon getting everything back together, I started putting it all back together in order to take it out on the water again and test it out for a longer period of time. With some work, I got her started and headed out on the river, only to find that I didn't have a great deal of power, therefore I throttled down and allowed it to warm up a little more. Once it warmed up, it seemed to provide a little more power and I headed on up the river. Still not moving as fast I was going the previous day during the test run. After about 15 minutes, I could see mirage coming off of the engine cover which told me that it was extremely hot. I killed the engine and then removed the cover. I was barely able to due to the extreme heat and i could smell plastic burning. I immediately got the extinguisher ready and moved the fuel tank away from the engine and allowed it to cool down.

After about an hour, I inspected the engine and saw that several wiring components, along with the base of the coils that had melted due to their close proximity to the engine head.

Needless to say, i didn't bother trying to start it again and trolled back to the ramp.

The guy that I purchased it from told me that he had a new water pump installed prior to their decision to sell it, but im not entirely convinced that he isn't taking me to the cleaners. I have no idea why it would have gotten that hot without shutting down. Thermostat failure? Cracked head?

I guess overall, I am afraid that I may have killed the engine for good by running it and allowing it to get that hot. I have tried to check compression, however this is with the engine cold and the best I can get out of both cylinders is about 35.

Thanks in advance for any help. Just looking to see what I am getting in to prior to taking it somewhere and being once again taken to the cleaners.

On a brighter side, The boat is in good shape and I am happy with the way it is set up, along with the trailer. So the motor may just be a wash on that purchase. It kills me as being active military, I am on an extremely limited budget.

 

[Grub54891]

How long was the test run? If it was going to overheat the first time out, it should have within 10 minutes. The part you say "once I got it back together" makes me wonder what ya took apart?

 

[Ihateclevernames]

The test run was about 15 minutes.

I figured the same as well. Unless of course it was some freak incident where something happened to fail after the test run during the time that I was running it at the house.

Didn't take much apart, disconnected the battery, moved the starter over a few inches and removed the carburetor in order to inspect it.

With that being said, I did notice that based on the pictures and diagrams I was able to find on this forum and several sites...............the guy that worked on it last had no freaking clue what he was doing. Things where bent and jimmy rigged in order to get the choke to work properly. It appears that the engine did once have an electric choke, however it was missing pieces, there fore things were bent and rigged in order to get the choke handle to engage the choke lever and close the carb.

So after taking it off and going through the carb and finding that it was in pretty good shape (as I was told) , I replaced it on the motor. The biggest issue that I saw was the manipulation of the levers, springs and other components on the left side. I carefully bent them back to the way they were depicted in pictures on line and managed to get the choke lever working somewhat properly.

After i put everything back together, I changed the lower unit oil (from the bottom up) and them fired it up. It seemed to only want to fire up with the throttle wide open, and then backed it off to the point that it wanted to die and then adjusted the mixture in order to get a decent idle.

Thanks for the quick response.

 

[Grub54891]

Hopefully it isn't toasted, sounds like it is though. The crab/timing sink and link has to be spot on, or that will happen. Bummer.....

 

[Ihateclevernames]

So basically, what could have happened in order for it to come to this? Could it have been this way prior to the test run and then just amplified the longer I ran it?

So, with that being said.........

Where should I go from here? Should I run a compression check to see what comes back? Should I take it in somewhere and have them diagnose it?

I am guessing that based on how hot it got that i will have to at the least...........

Replace the coils
Replace the power pack
Check the wiring
Have the links, springs and choke levers replaced

and at the most...............

Replace the piston rings?
Basically rebuild the entire powerhead?

 

[F_R]

You might as well accept reality. You toasted the pistons in that motor. Nothing short of a powerhead rebuild is going to make it run reliably again. Needless to say, also find out what is wrong with the cooling system. BTW, you suggested it should have shut down automatically when it started to overheat. No so. There is no such a device to do that. At least not on that motor.

 

[Bosunsmate]

Pull the head, maybe i havent read this all correctly but perhaps the head gaskets gone and not much else has being damaged.
Inspect the cylinder walls

 

[Bosunsmate]

BTW, you suggested it should have shut down automatically when it started to overheat. No so. There is no such a device to do that. At least not on that motor.

I was thinking if you hooked up the overheat sensor (one that was working) to the kill circuit that would cut the engine

 

[Grub54891]

I was thinking if you hooked up the overheat sensor (one that was working) to the kill circuit that would cut the engine

You can hook up an alarm that will go off if it gets to hot, it'll tell ya to stop before the damage is done.

 

[F_R]

What bosunmate said is an interesting idea. Might even work, if it doesn't cause an ignition problem at normal temp. However, the motor under discussion has no overheat sensor. Maybe one can be added. Interesting. However, my experience with the factory sensors is that they are extremely unreliable. You wouldn't believe how many motors I've seen with the paint burned off the powerhead and the alarm never went off.

 

[tomhath]

When you were testing it before heading to the river, was it pumping water? Please don't say you ran it without putting it in a barrel or muffs on it.

 

[Ihateclevernames]

Yeah, I was running it with muffs on prior to taking it out.

I guess all in all, trying to figure out what happened in order to cause this is my major concern. Obviously it is something that I did, because I ran it and allowed it to get to hot. However, what was actually making it too hot is the question.

Hard to believe that everything was fine with the exception of the choke during the test run and then after tinkering with that, I managed to kill it.

As you guys stated, a powerhead rebuild may be required. Is it worth it on this engine? I don't exactly have the $$$ to flat out purchase a new motor for this boat, but could stand to put a little bit into repairs.But from the sounds of it, we are talking a pretty significant chunk of change.

I will take a few pictures later on of it.

 

[Tim Frank]

Gents, first time poster.............long time lurker. A good amount of information has come from this site in the past and I hope to gain more insight from some of you "old salty" dogs out there.

Seems like you missed the numerous posts in here where the 'Old Salty Dogs" strongly recommend an on-water test before buying, or at least a good visual inspection and test run in a barrel.
From the description of all the problems that you found during your post-purchase visual inspections, the clues were all there if you'd looked carefully.

Running it on muffs and a hose is not really going to tell you whether it is pumping water on its own. The most likely cause of all this is the cooling system not working....clogged pathways (is this a saltie) , suction obstructions or similar. Nothing you posted suggests that you checked the cooling system output while on the water.
I'd guess that the problem existed on both trips and you just missed it the first time....and/or the trip was shorter so the o/heat was not as severe.

It also sounds like an OEM manual (also frequently suggested by the OSDs) would have saved a lot of grief.

At this point a compression test might show that you got lucky, but FR knows his stuff.

 

[Ihateclevernames]

Yep. I am secure enough to know that I screwed up and didn't dig into it enough prior to purchase.

The first test run wasn't nearly as long as the second run after purchase. Overall, I was more concerned with the boat than I was with the engine as i got somewhat overzealous after running it on the test run.

That being said, what is done is done. Buyer beware is the old saying..............and I wasn't aware.

So now, I have started digging into it a little bit and pulled the thermostat and took a look under the head. The top of this pistons seem somewhat charred, however on the sides, they look pretty clean. However that is not to say that the rings aren't shot. They cylinders are smooth and I don't feel any gouges in there or anything like that.

The gaskets on the other hand are trashed. Charred as can be and pretty much unusable. I am going to throw the thermostat in a pot of water to see what happens, and I will post the result.

 

[Ihateclevernames]

Thermostat failed to open up at 212 degrees, so I pulled it out. I am guessing that the opening would be somewhat significant on the end where it is supposed to open up, where as mine failed to open at all.

Could this have been the cause for overheating or potentially been damaged during the time where it overheated?

 

[oldboat1]

sounds like post mortem, but anything is possible when stuff is melting.... On the positive side, think there should be a number of powerheads that would bolt up, 70s-80s. Depending on what was destroyed, you can probably convert a manual start donor motor with your electric start components -- have a number of possibilities.

 

[Ihateclevernames]

sounds like post mortem, but anything is possible when stuff is melting.... On the positive side, think there should be a number of powerheads that would bolt up, 70s-80s. Depending on what was destroyed, you can probably convert a manual start donor motor with your electric start components -- have a number of possibilities.

Exactly what I was thinking.

After looking a little bit closer, I noticed some cracks between the ports are inside of the head. So yeah, im thinking it is done.

I would assume that the lower unit is still good and there are a number of parts that can be reused it possible.

I found a similar model that has a few issues close by, however I am not sure if it will be compatible.

I currently have a 1981 Johnson 35HP Sea Horse with electric start

He has a 1976 Johnson 35HP with electric start, and his ad can be viewed here.

Would a number of my parts be compatible with this particular engine? Or would I be better off getting something new such as a 4 stroke? I am actually quite fond of the idea of digging in to this engine and learning it in order to use it for years to come, however I don't want it to turn in to more of a money pit than it already has.

Thoughts?

 

[oldboat1]

into apples and oranges if deciding whether to buy new. Different game (and can blow up a $10,000 motor too, which would presumably be harder to swallow). The '76 will have some differences (ignition). It sounds like you might be looking for a replacement motor rather than a donor -- which is fine. That particular motor sounds like it might be a little rough.

 

[sutor623]

Yea that guys dreaming if he wants $475 for that motor. Won't shift into reverse and coils are going bad? Troubleshooting ignition problems is touh for the average joe. Sumthin tells me he is selling that motor cause he can't figure out the problem. If compression is good on that motor, it may be a good head donor. But I wouldn't pay over $300 for it out my way. If that

 

[bonz_d]

In my area it would cost more to rebuild than replace. Could start watching for a used one with a blown out lower unit. Which in my experience is normally the case with these engines. Just remember that the one you have will only swap over about a 4 year period, I believe it was 1980-1984.