Expert: Jeff Grigg - 1/9/2008

Question
Hi Jeff. I have just had my Johnson 115 repaired after picking up metal on my two top pistons. There was no indication of overheating and I had just had the carbys serviced. The repairers immediately told me the reason was old fuel/oil, lack of maintenance, but when this was discounted, they blamed a collapsing fuel line for the engine "leaning out". My insurance assessor says that there is no chance of that. On my first run after a $4.5K repair bill ( 2 pistons, rings, bearings and head rebore) the motor overheated during the breakin period, 10 sec into a full throtle run in the third hour. The repairers have blamed and replaced a faulty heat send unit. I have done a short ( 2kl) full throttle run with them since. However I will be taking my boat out with crossed fingers until my confidence in the motor is restored. My question is do I believe my repairer about "leaning out" melting down my pistons or is my insurance assessor correct that this can't happen on a motor of this size?

Answer
Without checking the engine myself there is no way to tell. Just from what you have posted I don't trust the repairers. Any time you have a major failure like what you had the techs MUST find the problem. They just can't guess. This means checking everything from the fuel tank back, all the senders etc.
The should know what caused the problem.
A restricted fuel line, such as what could happen with a sloppy carb rebuild could lean out the top two cylinders, but it would be very rare, and you should notice the problem long before any damage was done.
Since it was the top two cylinders I would have suspected overheating from the beginning.
Were the thermostats checked/replaced? Water pump? Corrosion under the powerhead? Blown head or exhaust gaskets etc.
I feel your repair bill was excessive, and the shop did a bad job of diagnosing the problem.
Take the engine back to the shop and have the check out all the senders etc. There should be one for each cylinder head. Something still doesn't smell right.
Post back with what is found if you need more help.
Jeff