90hp Yammy

[Crappie Reaper]

Ok, I'm going to trade my shock collar setup for the Charger bass boat with the 90hp Yamaha on it. I pulled the plug on the lower unit yesterday and the oil on it appeared to be clean and clear. The outside of the motor under the cowling is very clean. It has three cylinders and two of the plugs are brand new, the third looks as if it had been burning clean with no visible shavings on it. The guy said the boat belonged to his brother who had it underway on the Verdigris River here in Oklahoma, when the thing just died. The motor itself is locked up and will not turn. CrappieDentist has suggested that I raise the motor up as far as it will go and spray WD40 into the cylinders and let it stand for a couple of days. Then take a breakover bar to the nut on the flywheel to see if it will break free. My guess is that this motor may need a head unit, along with a bit of boring.

I am open to suggestions as to what can be done to troubleshoot what's wrong in the simplest manner.

[Barnacle Bill]

Since it can be the lower unit causing it to seize, I would pull it first. You are going to need to replace the impeller anyway if you get the motor free. Then proceed as planned except use PB Blaster unstead of WD-40. Its 100% better and available at your local Advance Auto. If you get it free run a compression check and see what you have.

[Scrapper]

Thumbs up on PB Blaster...Way better than WD-40. We haven't bought that for the shop in a few years. Sea Foam Deep Creep is also an EXCELLENT product although mores expensive.

So you say one plug was clean?? As in no oil?? Now shavings is good. Maybe if its has low compression it can take just a honing...need to get it scoped.

Take the lower off first like ibnfshn said. They can lock up and the motor won't do anything. Think you made a good deal there. Ecspecially if the lower unit checks out good. People love yammies!! Wish I had one...lol.

[Crappie Reaper]

What would be less headache to repair if at all possible? The lower unit, (replace), or rebuild the motor?

[Scrapper]

The lower unit! A lower unit would not be bad...if there are not any shavings in it and the oil is clean I bet its okay. Can you put it in neutral?? If its bound up you won't have a neutral...if motor is froze you will still have a neutral.

If you do not have any deep gouges in the cylinder wall...meaning you could just bore the one cylinder it wouldn't be too awful bad...if you have to sleeve it you get into bigger $$

If you do go ahead with this hit up iboats and ask around. DO NOT use an automotive machine shop...only a marine one that specializes in outboards. There are different things you do to an outboard block that you do not do to your typical automotive block. If you get here free....first and foremost..pull the head and examine. Make sure there isn't a piece of a ring or something laying in there. If you try to start it or you do a compression test and soemthing is beating around in there you could have even BIGGER problems than you would've.

If everything looks to be clear in there....replace head and gasket...torque it down to whatever its supposed to be...then do a compression test. If any of the holes are very far from 10% off from one another....ie...100, 105, and 60...I'd start taking her apart to find the problem. As long as you have SOME compression...like 50 or 60 or something...you may get away with a hone and rering and maybe a piston....if you have 0 or somewhere there abouts...you looking at a bore or sleeve probably. You will probably find you have a good score in it...if its gouged really good it will have to have a sleeve pressed in. Either way it won't be cheap...but would be cheaper than a new one if all else if okay...and yammies are good motors.

When you tilt it up and spray...do this over a period of two or three days. Don't do it and an hour later start trying to turn it. Spray every 4-5 hours or so....let it sit for 2 or 3 days...penetrating oil works MUCH better if you let it sit for a good long while. If the rings are savagable they will thank you also.

Just a few thoughts...let us know if you need anything else!

[Crappie Reaper]

I don't plan on trying to save the motor if something like the lower unit, or an rebuild is in order. It's not worth the time or the cost for an '84 model. I believe it's the first year Yamaha made outboards. If I check things out and it's going to be costly, then I think I'll just start placing parts of it on ebay. The tilt and trim works fine. If I find that it would be a minimal cost to repair, that's an option that would interest me. If not, no biggie. The collar setup I traded off to get the boat, motor and trailer cost me about $425, 6 years ago. I'm fairly certain I can make that back, plus some.

Thanks for the info and help. I will try the above suggestions and give a report back.

[Slipcork]

My 1984 40hp Yamaha had a bad oil pump in 1994. That is when I bought it with a bad hole. That is before Wesco even had pistons for them. Had to wait on them to make them. But, we bored all 3 holes .30 over. That was in 94. She will turn bout 6k rpm and fly.

Call Glenn at K&K Marine, Hot Springs AR. 501-767-9128. Pull power head and ship it to him. They can hook you up with it. Mill the head, port it. You name it.

My website. Page 1 boat racing in Hot Springs.