Alpha one 5.7 I/O shifts fine, prop spins in gear at idle, no thrust under power

[Happy Hours]

This happened to me. Can anyone point me in the right direction?

While cruising at speed across the water the motor suddenly revved up. I Kicked it out of gear immediately. My first thought was the prop fell off. We were at the end of our 3day camping trip so lucky for me I was almost back to the boat ramp when it happened.

I could put the boat in gear and the prop would spin and move the boat at idle. Give it any power and the engine RPM's go up but the boat doesn't go faster. It's like it's in neutral. I limped back to the boat launch.

While on the trailer I shifted into F. The prop can be rotated clockwise and clicks while you do it up in the transom area. I read in another posting that the click sound was fine. Shift into reverse and the prop turns countr clock wise and also clicks. The prop cannot be spun the opposite direction while in gear so I ruled out the prop having a spun hub. Can anyone concur this could be ruled out? I didn't hit anything with the prop before this happened either.

I have read that the engine coupler would be another item to investigate. A previous post said you would smell burning rubber I didn't smell any burning rubber. I'll take a peak in the bilge and see if there are any rubber pieces.

The out drive shifts like always in to F and R. No poblems there, it's very smooth. I've owned this 1988 Bayliner Monteray for about 5 years and have kept regular maintenance and tried to do preventative maintenance along the way.

Any thoughts?

 

[bigdaddypt]

Re: Alpha one 5.7 I/O shifts fine, prop spins in gear at idle, no thrust under power

I would still consider a spun hub. Put a line on the hub and prop that is lined up. Do it with something that won't wash off. Put it in gear and wait for the situation to happen and see if the mark is lined up still. If not, spun hub, if so it's another issue.

 

[fishrdan]

Re: Alpha one 5.7 I/O shifts fine, prop spins in gear at idle, no thrust under power

Sounds like a spun prop hub to me. If it's spun, chances you won't be able to make it slip by hand, so trying that isn't a good test. Remove the prop, scratch/mark across hub and prop, reinstall the prop and take it for a short cruise, enough to get it to slip. remove the prop and see if the marks still line up, they probably won't.

If the prop uses a Torq-Flo hub insert, you can replace it yourself.

 

[generator12]

Re: Alpha one 5.7 I/O shifts fine, prop spins in gear at idle, no thrust under power

There have been other posts about identical situations on the forum. Virtually all refer to a "spun prop". You can't necessarily identify a spun prop by hand. The torque requirement to break it loose is not easily replicated in the driveway, but it happens under load. What you describe is almost certainly that.

If you have access to another prop, try it. If not, you should probably get one anyway just to have a spare. (I have three.)

Good luck bud.

 

[Happy Hours]

Re: Alpha one 5.7 I/O shifts fine, prop spins in gear at idle, no thrust under power

Took the prop to a shop this morning. Upon further exam it was in fact a spun hub. After cleaning the prop up some there was rubber around the base of the nut. It was black rubber and blended well with the grease. After scraping it off you could see it was a spun hub based on the area the rubber was found. Bought a new (2nd) prop and having the old repaired.

Thanks for all the replies. I learned something today.