Seized motor frees itself

[preaney]

Had a strange problem recently with my ?86 Force 125. Was out on the lake running at WOT for about 5 mins when the motor seized - or so I thought. Was at full throttle one second, then a clunk noise, and it stopped. Could not crank the engine and could not turn the flywheel using a wrench on the bolt on the top. Prop turned freely when trying to crank/turn flywheel. Don?t think we hit anything as there was no damage to the skeg/prop/lower unit. Was using last year's gas but had stabilized it and oil mix was fine as far as I knew.

I figured that the motor was shot. Hadn?t checked for coolant flow when taking boat out as I usually do, and thought I had overheated it and warped it until it locked up.

About eight hours later, my son tried cranking it and it had miraculously freed itself up. Cranked it for a few secs and it fired up. Let it idle at the dock for about 10 mins, and was pumping water just fine. Took it out for a test run and was fine at low rpm, but made some unusual noises at higher RPM (sounded like a scraping noise). Shut it down for fear of more damage.

Got it in the driveway and removed the lower unit drain plug ? lots of water in the lower unit. No metal shavings visible in the cylinders from the spark plug holes.

So what I thought was a powerhead problem looks like it might be a lower unit problem instead (or both).

Is there anything that could happen to a lower unit that would stop a motor cold from full throttle? I would think that if something locked up in the lower unit, 125HP at full throttle would shear something and the motor would keep going.

 

[Frank Acampora]

Re: Seized motor frees itself

I had a 125 that stopped dead at full throttle. It restarted and ran fine for a couple of weeks, then under full throttle, the prop shaft broke inside the case. Upon tearing the engine down, I found one piston with 1/3 of the lower ring on #4 cylinder missing. Of course, I also found the broken prop shaft. Because of the wear in the reverse gear, I suspect that the broken ring and prop shaft happened at the same time (The immediate stop with a heavy Stainless prop snapped the shaft) and the shaft jammed itself together well enough to run at partial throttle. The real surprise was that the broken ring did not score the cylinder even though it messed up the ring groove. I was able to replace the piston with another used one I had. However, the reverse gear hub (center) was worn enough to be totally useless and the land on the shaft which bears against the reverse gear center only in reverse (normally) was also worn almost all the way.