1980 Johnson 150 V6 Broken Crank

[rdomeck]

I have just acquired a tri-hull pontoon that has a model #J150TLCSR. The best I can tell is that it was made in 1980.

I have not brought it home yet, but did stick a battery in it and when the starter spun very fast I pulled the cover to find that the flywheel had broken off at the crank. I will be looking for a crank and flywheel, but plan on tearing into it to find why the crank broke in the first place. Everything else seems to be operational with it and the boat itself is in pretty good shape.

My question is, do these have a problem with breaking the cranks? I have been a mechanic for many years and have built a lot of engines, but non of them were 2 cycle boat engines. My experience is that crank just don't break. There is generally a reason for it.

Thanks for any help or advice you guys (or girls) can lend.

[boats.net]

The crank breaking is not a commen occurance, I am uncertain what may have caused the crank to break.

[rdomeck]

Thanks

Thanks for the response. I just got the boat home and will start researching parts for it this weekend. I did put it in gear and turn the prop. Much to my surprise the engine does turn over and seems to have compression. Guess we will see what is going on with it!

[rdomeck]

Got it apart....

I was able to get the engine apart and have found two different bore piston's in it? I don't think it's right, but wanted to ask. I have 3 pistons at .020 bore and 3 pistons at .030 bore. I don't have my bore gauge at home, but I'm assuming that the cylinders match the pistons.

Is it normal for people to do this in 2 cycle's? I wouldn't do this in a 4 cycle for sure. Luckily the one cylinder that is scored is one of the .020 bore's and hopefully I can get 3 of the correct size pistons and bore the 3 cylinders out and put things back together!

Thanks for any input, Randy

[boats.net]

That motor has been rebuilt before. Someone used oversized pistons.

[rdomeck]

Piston overbore

I realize that the engine has been rebuilt before, but I'm wondering is it common practice to have two different sizes of pistons?

Thanks, Randy

[Dawgs226]

So why did the crank break?

[rdomeck]

Not sure

I'm not exactly sure why the crank broke. One of the pistons is scored, but not enough to cause it to seize. Could have even been some beating on the flywheel with a hammer trying to get it to start.......The engine still had compression and some of the cylinders although I didn't do a compression check. Luckily I have been able to find all of the parts to fix it locally. Still more money than I was hoping to spend.

Seems like this is what boat ownership is all about. Work on it every weekend for a year to be able to use it 5 times the next year.....Hopefully my family will enjoy it once it's done!

[Dawgs226]

Well i rebuilt my 1986 so i hope i can help