It was running fine and clank,clank.... cloud of white smoke and Crap ,WTF, locked up. Dealer is looking it over now. I can not see investing a lot in to the motor as it is a 1989. it is on 18 foot starcraft sfm 180. I stopped at three places and used motors are not to found so far. Any ideas? I am in the N.E corner of Iowa.

Try craigslist.org Pick minnesota, then pick mpls/st paul., Pick boats or in the search just punch in mercury.

Is the motor the 6 inline or 4 cyl?

It is a 4cyl. inline. The top two pistons were seized up and tore up the jugs a little.Number one is worse than number two. Looks like a rapid overheat engin failure. But no mechanical reason found that would have caused it.Weeds around the water inlet or a trash bag ect??? is what the dealer thinks. Insurance is paying for a rebuilt powerhead.