Spun prop or something else?

[bizron]

Hey guys,

While out on the lake this past weekend, we experienced some trouble with our 1991 Bayliner Capri. Hopefully you guys can chime in on what you think could be wrong with it.

We were cruising along at a good clip (deep water) with the outdrive trimmed up. Without warning, the engine RPMs surged and it felt like the boat lost it's forward thrust. It seemed to me like it had somehow popped out of gear, so I backed the lever back to neutral quickly.

Outside of the engine RPM surge, there were no weird grinding/popping sounds. After I shifted back to neutral, I coasted a bit and decided to try shifting back to forward. I got the familiar "feel" of shifting to drive with the lever, but I didn't feel the typical feedback from the outdrive.

I could tell something was wrong because when I pushed the lever forward, the engine RPMs increased as expected, but there was zero thrust coming from the outdrive. I feared that maybe we had lost the propeller....

I trim up the outdrive all the way and find the propeller still attached. I climbed to the back and got my brother to try to engage the drive while I watched the prop. Zero activity with the prop selecting forward or reverse.

After trying to think it through, we checked the shaft going to the outdrive and it was turning fine. We decided to shut down the engine and play with the propeller some.

With the drive in neutral, the propeller would spin both ways freely with no weird sounds.
With the drive in forward, the propeller would lock one direction and ratchet the other.
With the drive in reverse, the propeller would behave exactly opposite of forward...ratcheting in one direction and locking in the other.

The behavior of the prop suggested to me that if it locked in one direction, that the gearing/shafts were still working as they should. I'm mechanically inclined, but I've never opened an alphaone outdrive, so I could be way off.

There was a theory that maybe we had spun the prop hub and that was our problem. A bunch of people with spun props seem to suggest that the prop does move some, but starts slipping above a certain RPM. Our prop doesn't move at all.

After the tow of shame back to the dock, we took her home and removed the prop. It didn't look burned or melted. There was no real indication of damage that I could see. I've seen that the older props can have problems even if they look fine on the outside.

I wouldn't suspect it's a shift cable issue because the drive does react to forward/reverse/neutral selections.
I wouldn't suspect it's the coupler or anything drive-shaft related because the chain of power seems to hold up all the way down to the prop.

The prop seems fine to me but it wouldn't turn at all in water, even trying to just idle in drive.

What would you guys think is the problem? Thanks for any input!


1991 Bayliner Capri (21 ft)
4.3L V6 Mercruiser
AlphaOne outdrive
13 3/4" 21p prop

 

[ktbarrentine]

Re: Spun prop or something else?

I'm putting my money on stripped gears in the upper drive. Drain the OD oil and let us know what you find. If you are mildy adventurous, you can pull the top cap off the upper and peak inside. (That's my crystal ball forecast based on your description so far).

 

[Bt Doctur]

Re: Spun prop or something else?

low oil in the drive melted the gears, you would start to overheat cause pump is not turning
a previous hard strike caused the driveshaft to snap, no gears but normal cooling

 

[ktbarrentine]

Re: Spun prop or something else?

Hmmm..yup...didn't consider the temperature aspect, but got no description of any temperature readings (good or bad) after the power loss (if you ran it enough to tell)... That may help to narrow it down some more. Probably a good idea to pull the drive and give 'er a good once over and see what it looks like split apart. When was your last drive pull and routine drive maintenance action?

 

[thumpar]

Re: Spun prop or something else?

Could also be stripped splines in the coupler. It should be pretty easy to figure out by pulling the drive.

 

[bizron]

Re: Spun prop or something else?

Thanks for the input guys!

Temperature readings weren't monitored closely enough to say if cooling was affected or not.

It'll be Sunday before I can get back to pull the outdrive, but I'll see what I find and report back.

I'd like to put some muffs on her and see if the prop spins, but I have a feeling that nothing will have changed. The shaft is turning as it comes out of the engine, but who knows what is going on after the shaft disappears into the outdrive area.

Since putting it in gear works (the way it ratchets), it really does seem like gears would be stripped or something inside the upper unit. I would expect to have heard some kind of pop or grinding sound if gears were shearing off, but where it's outside the boat and near the water, who knows if I would've heard it or not....

Thanks again for weighing in!

 

[thumpar]

Re: Spun prop or something else?

If the drive shaft is spinning but not the prop while in gear it is something in the that broke and not the coupler. You can take the top cap off and have a look at the upper gears.

 

[bizron]

Re: Spun prop or something else?

Alright guys - sorry for the delay.

We took off the top cap and noted that the bearings looked to be fine. No chewed up gears or anything was visible from the top.

After draining the oil, I didn't notice any massive chunks of metal flowing out the drain of the outdrive.

We removed the outdrive from the boat and verified that the drive cable was moving properly. After separating the upper/lower, it still wasn't clear what was wrong. Turning the drive shaft in the upper caused movement in the gears and caused the vertical driveshaft to turn. Shifting the lower unit manually caused the prop to ratchet and lock accordingly, so something had to be up.

After working my way down, disassembling the impeller housing, etc. I quickly found the culprit. The vertical drive shaft has snapped underneath the impeller section, but above the lower gears.

Some searching around proved that by the time you buy a new vertical drive shaft, new impeller kit, special tools for assembly/disassembly, etc. it was going to be cheaper to just buy a new SEI unit....which is what I did.

Yesterday we managed to get everything lined up just so (took multiple attempts) and after filling the unit with oil, we now have a properly shifting outdrive again. With any luck we may get to start the break-in procedure this upcoming weekend.


So how does a vertical drive shaft break like that? Well, the boat was loaned out to an inexperienced group (family, sigh) and they didn't know how far to back the trailer down the ramp in order to get the boat back on the trailer. My mother who was with the group admitted later that they had dragged the propeller on the boat ramp while the engine was running. There was no mention of the incident, but I did remember noticing the prop had burrs on it. I suppose I should've pressed for an explanation, but ideally they would've just been honest.

The prop is stainless steel, so even though the prop showed signs of damage, the real damage could've been transferred on up the chain. I suppose an aluminum one would've just broken. I'm not sure, but I'd suspect that the vertical driveshaft must've suffered some kind of hairline crack in it. Then as we were driving across the lake and the outdrive warmed up, a few key waves of resistance may have stressed the vertical shaft just a little too much.

We may never know exactly what caused it to give up...

 

[thumpar]

Re: Spun prop or something else?

Was your skeg missing? The skeg should have hit first that is one of is purposes.

 

[ktbarrentine]

Re: Spun prop or something else?

The vertical drive shaft has snapped underneath the impeller section, but above the lower gears.

Wow...hadn't heard of that break location before, but sure others have seen this phenom. Breaking there would allow your water pump to still work, so lack of a temp excursion coupled with the loss of propulsion starts to help narrow things down. (I am more familiar with the typical vertical shaft break point at the O-ring groove just below the upper gears on the "older" drives (pre 1991)... which then causes an overheat condition as well as loss of propulsion).

Glad you are ready to splash again! Best of luck!

 

[bizron]

Re: Spun prop or something else?

Was your skeg missing? The skeg should have hit first that is one of is purposes.

It wasn't missing completely, but it was way smaller than the SEI unit's skeg. I never realized just how much was gone until I compared them.

Thanks everyone for your insights.