1985 40 hp ELTK dropped compression in middle cylinder

[bama]

I have a 1985 Lund Tyee 5.3 with factory installed twin Yamaha 40's. I LOVE this setup(except for graph transducer mounting). My last trip, the motor quit on me a few times at full throttle and when I tried to start it the last time, it didn't sound right. After the fishing trip, I tested compression and had 20 pounds. 120 on the other 2 cylinders.

I am a frugal man. I like this setup. I teach small engines and am quite comfortable doing overhauls on small equipment and have done heads on my 350 TBI in my pickup.

The price of updating just doesnt' make sense to me. I am considering rebuilding this engine. I know it is old. What could be the drawbacks that I am not seeing? I went through lower units when I bought the boat in 2018. Trim and tilt works great and I went through those as well.

Dropping $5-6K on a new engine just won't fly. I like to fish, but that is a LOT of FREE fish to catch.

Thanks for any advice given.

 

[R_P]

If you are comfortable with engines the only drawback I would see is removing bolts that in my saltwater environment do not like to be removed after so many years. If in freshwater it should be a LOT easier. Tear into it to see what you have to work with and go from there. If everything comes apart nicely and all you need is to rebore the block for oversized pistons you would be ahead moneywise. The real issue becomes WHY did that cylinder self destruct and how do you prevent it from happening again

 

[bama]

Freshwater motor its whole life, luckily. Mostly Minnesota and North Dakota. I was hoping to hear rebuilding something this old is not crazy.
They are not too smoky and darn quiet for being 2 strokes. They will idle all day long for trolling.

I always check the why when I rebuild a chainsaw. Other then rebuilding carbs, replacing all oil and gas lines, and changing spark plugs, this thing has not been touched. It turns over smooth so hopefully the crank is fine. I am assuming on these, the rod mains are not replaceable. I will be curious to see what it looks like. In a week or two I will tear into it.

Thanks for the response.

 

[racerone]

Are pistons available from the Yamaha dealer ?

 

[boscoe]

Rebuilding something that old can be worth it. For the learning experience if nothing else. Then there is the sense of satisfaction of having done a repair on your own.

You are going to have to open the motor up to see what is the problem. Then decide to repair the block or scrap it.

If Yamaha OEM were available I would not use them. I would use aftermarket pistons and rings. The older a motor is (and the less valuable it is) IMO the less the reason to use OEM high priced parts.

 

[bama]

Rebuilding something that old can be worth it. For the learning experience if nothing else. Then there is the sense of satisfaction of having done a repair on your own.

You are going to have to open the motor up to see what is the problem. Then decide to repair the block or scrap it.

If Yamaha OEM were available I would not use them. I would use aftermarket pistons and rings. The older a motor is (and the less valuable it is) IMO the less the reason to use OEM high priced parts.

I found aftermarket as an entire rebuild kit. The cost is what is attractive to me as to repower this boat with same HP would be a 90 horse if I went single engine. Saw a used 10 year old 4 stroke for $8000.

I can get the kit for less than $500. Then it’s just machining(or finding another block) and making sure crank is good.

I don’t mind the little bit of 2 stroke smell I get when running. As a former wood burner, I lived on that stuff.

 

[bama]

Are pistons available from the Yamaha dealer ?

I saw aftermarket but had not looked oem. I guess I’m used to aftermarket from the chainsaw side.

 

[bama]

UPDATE!!!

I took the motor apart today. I am including some pics. #2 is the bad one and #3 had scoring as well. Crank bearings feel good. There was Carbon on the top one which cleaned up easily. Big end bearings are free, but the small end rod bearings are bad on the #2 piston. Head looked good and seals didnt seem damaged. There is a piece missing, I think, in the casting on the oil injection after the carb but this did not cause the failure.

So, looks like it got hot and then aluminum transferred to the cylinder. I do plan on putting in a new impeller, but the old one is good and it always had a good pee stream. I had not replaced the thermostat and it was original.

Nothing has been touched on this motor. I had to crack open all the paint covering all the surfaces.

IS there anything I should be looking for that I would not think about if it were a chainsaw engine? I am used to working extensively on those of that era. I think I could go up to .030 over but would try for less. Next step is to find a machine shop unless I am missing something.

 

[bama]

I dropped it off at the machine shop. I also noticed the brass oiler gear in the crankcase was almost wore through. Since #2 melted all the way around the cylinder, now, I am guessing it was not enough oil?