81 Merc 140 stops at WOT

[SSTKO81]

Its that time again. And I'm addressing an issue I had at the end of the summer. When I'm cruising at WOT, for no apparent reason the engine will suddenly rev up and forward motion will just stop. -Almost like my prop fell off, but the engine doesn't die or anything. So I'll pull the throttle back to neutral and hit it again and i can cruise(sometimes for several minutes at WOT) and it will do it again. I was considering a prop hub problem(?) Drive gear somehow slipping(?)

-and I appologize, I just realized I put this in the outboard section, rather than the I/O sterndrive forum.

 

[1979checkmate]

Re: 81 Merc 140 stops at WOT

well, it has to be a gear slipping out or a prop hub failure. I would think you would hear a gigantic thunk when the gear reengages though, if not, my first guess would be a hub failure. Try this: take a permanent marker and draw a straight line from the prop, onto the hub. go run the boat, once you experience the issue again, lift the motor up and inspect. If the permanent marker line is no longer aligned on the hub and prop, you have a spun prop hub. If it is still aligned.. look into a lower unit issue $$.

 

[SSTKO81]

Re: 81 Merc 140 stops at WOT

Well I do tend to get a "thunk" when i put it in gear, be it FWD or REV. Especially when I shift slowly it will chatter a little in the shift, then "thunk" into gear. It done this for years and I always thought it was normal. Now I'm wonding what the lower unit issue could be if that's the case

 

[j_martin]

Re: 81 Merc 140 stops at WOT

It's supposed to clunk into gear. If you let it chatter, it'll get to end of life much sooner. It's a metal to metal dog clutch, and the rubber hub in the prop will soak up any potentially damaging shock at idle.

Do the prop marking trick as instructed. There are no clutches in the drive train that can slip. If it were gears, it would be a lot noisier messier, like parts out the side. It's likely just a worn shock hub in the propeller, easily replaced while you wait at the prop shop. (Takes a pretty good press setup)

 

[SSTKO81]

Re: 81 Merc 140 stops at WOT

Thanks for the help guys. It's in dry doc now. can I put it in gear and try giving the prop a turn by hand? Should end with same results, right? I know the prop has gotta be at least 20 y/o and I was looking forward to getting a new 4 blade anyway, so maybe this is a blessing in disquise...

 

[SSTKO81]

Re: 81 Merc 140 stops at WOT

I tried putting her in gear and twisting the prop by hand the other day. I think those blades would have cut my hand off before they moved. I couldn't turn it a milimeter! I'm sure I don't have nearly the torque of a 140hp Merc in my forearms, but I figured I'd get some kind of movement. Maybe not? Any other possible issue it could be?