Blown piston on a 1990 Johnson 9.9

An uncle of mine recently bought a boat with a 1990 Johnson 9.9 on it. He ran the motor 3 times with the motor running perfectly. Fourth time out it fired right up and idled great but when he tried to throttle up it would choke out and die. He took it to a mechanic up there and he got the news today that it has a blown piston. I have never gotten that far into working on a motor but thought I would ask you guys if you think it is worth repairing or is he better off buying a different motor. The mechanic told him that the piston is no longer made and can't be found, but I found one that is supposed to fit on ebay for $35. What else would I be looking to do while I am in there?

Define "blown".
Did it break or burn a hole in it? You need to determine what caused the problem.
If the cylinder,bearings & crankshaft are all ok you might get by with piston,rings,crank seals & gaskets.

I realize we are looking at what is essentially second hand information.
Usually, when a 2-stroke pops a piston, the first thing to go is the idle quality. So....I question the validity of the troubleshooting of the "mechanic" or the quality of the information we are seeing.
Will be really difficult to give much help until more, and more accurate information heads this way.
Second....only the standard bore OEM piston is not available. The .030 OEM pistons are still available. Aftermarkets are available in both sizes. I see no big roadblocks so far.

Right now this is the best information I have. He was more than a little frustrated about the situation when I talked to him, so he wasn't real talkative. At this point he is talking about selling the boat and trying to break even on the whole thing, but I am trying to keep him from doing that. I would have thought that a bad piston would cause idle issues too myself. I will try to get some more info as soon as I can. Thanks for the quick replies.

Do not give the motor to the mechanic or shop that told you that it was a blown piston. There are some out there that will tell you things like that in the hopes of you just telling them to keep it. Then they will repair it and sell it. Get the motor back.

A compression check will tell you a lot

The mechanic offered him 50 bucks for the motor and thankfully he did not take the deal. I am going to get the motor in the next few days and check things out myself. I will take some pictures and post up what I find out once I have it back at my house and have a chance to tear into it. Thanks to everyone for all the help.

sounds like it has something in the high speed jet in the carb. Did you get the motor yet?

Steve

I stopped by yesterday evening to look the motor over. The bottom cylinder is locked up though I didn't put too much effort into it. I can see what appears to be a little bit of metal shavings in there. After talking to my uncle some more he told me that the mechanic said that when he tore it down it looked as if the cylinders were getting more oil. The said the cylinder walls, the pistons and the spark plugs were bone dry. The mechanic assumed that my uncle had failed to put oil in the gas, but after checking and making sure there was oil in the gas he was amazed that everything was so dry.
What could have caused the cylinders to not be getting oiled up? I am remaining optimistic about the damage not being too bad, but until I get it home I can't be sure. As soon as I do get it home I will post some pictures and let you guys have a look at it.

That is the major problem with two-cycle oil mixed with gas.

You can tell by the color of the gas, if it has oil in it or not.
BUT, there is no way to tell how MUCH oil is in the gas.

Hope you come out on the positive end

When the motor first started acting up he thought maybe he had gotten some bad gas so he dumped it and refilled with fresh gas and remixed the oil at 50:1 so there was the correct mix of oil in there....I just can't figure out why the oil hadn't coated the cylinder.

chrispbrown27 said:

When the motor first started acting up he thought maybe he had gotten some bad gas so he dumped it and refilled with fresh gas and remixed the oil at 50:1 so there was the correct mix of oil in there....I just can't figure out why the oil hadn't coated the cylinder.

Click to expand...

Maybe the first batch of gas did not have the correct oil ratio in it when it started acting up. Then he refilled with the correct ratio. The damage was already done.

Has anyone been using starting fluid on that motor?

Not that I know of, but he just bought it two or three weeks ago so no telling what the previous owner had done.

I finally got a chance to tear into it today. The mechanic had just left it partially torn down so a lot of the work was done. I forgot to take pictures of the cylinders, but the top cylinder was moving freely and the bottom one was seized. I could also see some small shavings in the bottom cylinder. I was still optimistic though.........and then I removed the fuel pump and saw this........


Not good.....this is the other side of the crankcase......


And the view from inside....the crank looks ok to me....what do you guys think?


So, thoughts on what happened? As I pulled the crankcase apart I found shreds of the bearing that went around the crank, but not really sure where the rest of it went. The cradle piece was completely missing.

Eeekkk.... slung a rod through the crankcase. I'm gonna guess that it's probably not gonna be cost effective to have a shop repair it. Are you considering repairing it yourself? Have you started on a estimate for the parts needed to fix it?

Ya' know, at this point it is 'search for another powerhead' time.
The crank is not good, remember it is a roller bearing crank.
Without seeing the piston sides I would say it had water in that cylinder at one point and was left with water in it until cranked.
Just a guess on my part.
While off, check the water tube grommets in the adapter that came out with the powerhead and see if they are pushed over, deformed and are blocking water flow. That will tell you more about how the engine had been run as well.

At this point I think he has decided to salvage what he can in parts and start looking for a new motor. I have looked around at parts and with the crank needing replaced I really think he would be better off selling what he can in parts and putting the money toward another motor. I did suggest holding on to the lower unit because he hadn't seen many long shaft 9.9's and if he could find a short shaft Evinrude or Johnson between 1986-1992 we could switch out lower units.
Thanks to everyone for the advice and help.