Merc 70 possibly blown up in driveway - stupid human tricks

Buzz Killington

Petty Officer 2nd Class
Joined
Apr 27, 2010
Messages
128
Motor is an oil injected 70 with an oil pump that still works (probably going to bypass it soon). I installed new controls this past weekend and was trying to get it running on muffs. Boat sat in the garage for 1.5 years while I restored it. I had a hard time moving the idle speed lever and I (in hindsight) suspect that it stuck open at the motor. Anyway, finally started running and was howling like a banshee. High RPMs. I assumed (wrongly) that it was excess gas I had pumped in while priming and let it go for a few seconds. Prop was spinning fast so just to be sure it was not in gear I moved it to F and then back to N. At the same time I realized it was time to shut it down and as I shut it down, or because I shut it down, I heard a bang.

Engine stopped dead. Powerhead was too hot to ouch. Starter would engage but it would not turn over. Let it sit and came back to it today. Removed lower - it spins. Removed plugs and shot PB Blaster into the cylinders. I can rotate the flywheel 3/4 of a turn with no problem but it will not go all the way around and there is a definite "catch" or resistance so I have not forced it.

I appreciate any advice. This broke my heart because I worked like a galley slave to get the boat finished for Memorial Day :/

Dave
 

Buzz Killington

Petty Officer 2nd Class
Joined
Apr 27, 2010
Messages
128
Thanks for the replies. Explanation makes sense. Any ideas of what it should reasonably cost a shop to rebuild?
 

Chinewalker

Fleet Admiral
Joined
Aug 19, 2001
Messages
8,902
What year is the motor? If a shop does the work, you're not likely to get out of it for anything less than $1500. If it's an older motor, you could find a lot of decent used outboards for that kind of money.
 
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