Opinions need on '85 Yamaha 90hp rebuild

[TNBassman]

I was out with my '85 15' Procraft Saturday and the motor a 85 Yamaha 90hp lost power and died. After a while I finally got it running again but it sounded different. When I got it home I did a compression test and found that the center cylinder was 50% of the other two. So I removed the head and found the piston liner was scored pretty bad. I need your guys opinion on what to do. Is it a very big job to replace the powerhead for around $2,000? I'm sure I can do it even though I have never worked on a boat motor. I have the Selco repair manual and decent mechanical skills. Or should I just let my local dealer fix it for around $3,500. This way I know it will be done right and what ever happened to make the piston fail will also be fixed. I was told by a coworker that what ever I do I should disconnect the oil injection system and just add the oil to my gas. Or should I just put the head back on, make sure it starts and trade the boat in on a new Triton.

 

[Osprey]

Re: Opinions need on '85 Yamaha 90hp rebuild

Bassman,<br /><br />Given that you are good mechanically and are comfortable going for it, the biggest issue you will likely face is broken bolts during disassembly.<br /><br />Is this a saltwater use motor?

 

[TNBassman]

Re: Opinions need on '85 Yamaha 90hp rebuild

No, I've only used it in fresh water. I don't know if it has ever been used in salt water before I bought it but it did have some corrosion in the water jackets and a couple of the head bolts had rust in the middle of the bolt. The only thing I'm worried about is finding out what happened. If I don't find out why it failed it could happen again. Of course it could have just been it time to go. After all it is an 85 model with who knows how many hours. I did a comp check on it when I first bought it and all cylinders checked out fine. Some thing that might be a clue is when it first happened I removed the intake cover off the carbs and found a pool of oil and fuel. It ran fine for the rest of the day except for a loss of power at take off.

 

[rodbolt]

Re: Opinions need on '85 Yamaha 90hp rebuild

hello<br /> with proper maint that oiling system will outlast you. 2000+ hours are not uncommon if the system is kept clean and adjusted. but if ya feel better then leave the pump drive shaft out at reassembly and premix.nost the time a fuel pump diaphram will leak and spray raw gas into the crankcase. which erver cyl drives the fuel pump bites the dust.like osprey says broken fasteners can be an issue. get good with a drill,taps and helicoils. its imperative to remove the exhaust cover and inspect the exhaust divider plate. a pin hole in the plate will spray water in a cyl and take it out as well. other than that rebuild the carbs,replace the fuel pump. replace the water pressure control valve grommet and water pump and you should be back in action. also check with some of the reman shops. hydrotek and southwest I have delt with. some posters here report good luck with iboats vendors.