Lost most of prop power

[deandec]

This is a 2000 Mercruiser 260HP carborated engine with an Alpha One outdrive. The boat ran fine for two hours. While pulling a tube rider at about 3,000 rpm, we heard a clunk and saw and smelled smoke from the engine compartment.

Checked the compartment for visible clues and found none. Guages all read normal. Fluid reservoirs were all normal.

The unit would shift into forward and reverse gears but would only provide an estimated 2 mph thrust for the 21' Maxum.

Great for trolling but not for towing.

The engine will rev up normally, but no additional thrust is available.

Can someone give me the likely component failures to investigate?

 

[Sparkinator]

Re: Lost most of prop power

Sounds like your engine coupler is gone.

 

[Cptkid570]

Re: Lost most of prop power

yeah, you probably either spun your engine coupler (where the axle from your outdrive goes into the back of your engine) or spun the hub on your propellor. You can test both of them by painting a line on them with fingernail polish or white out, then running the engine under load, and see if the line moved..

 

[wire2]

Re: Lost most of prop power

At the moment of hearing the clunk, did the thrust suddenly stop (the boat slowed) and the engine rev up? That does tend to point to a coupler. The smoke you mention is from the oil/grease getting hot from the friction of the coupler spinning over the splines in the shaft.

 

[Cptkid570]

Re: Lost most of prop power

Exactly.. but, as i said. You can test it. Just draw a line from the driveshaft onto the coupler with fingernail polish.. run it under load and then see if the line still lines up.. then again, if you aren't going more than 2 mph, you may be able to turn the prop by hand and see what is spinning...

 

[deandec]

Re: Lost most of prop power

At the moment of hearing the clunk, did the thrust suddenly stop (the boat slowed) and the engine rev up? That does tend to point to a coupler. The smoke you mention is from the oil/grease getting hot from the friction of the coupler spinning over the splines in the shaft.

As I recall, there was no rev up of the engine at the incident, just a sudden loss of thrust with the sound and light smoke.

We used the power train to get to the boat launch and load the boat on the trailer.

Since it is not near the water at this time, will I see the effect by painting the lines and running on a hose but in forward gear?

 

[SeanMcl]

Re: Lost most of prop power

Since it is not near the water at this time, will I see the effect by painting the lines and running on a hose but in forward gear?

No, there probably won't be enough resistance to twist the broken coupler or prop hub without being in the lake under load.

You can put the boat into gear, with the motor off, and try to turn the prop by hand. If it will turn, then you would see the lines on the coupler or prop move. But if it won't move, that only means you can't twist the prop as hard as the motor can. It could still be slipping under the higher amount of torque from the motor.

 

[Don S]

Re: Lost most of prop power

Just look at the back of the coupler if its all wrinkled and rubber bubbled and out of place, the coupler is dead.
The rubber is smooth on good couplers.

 

[deandec]

Re: Lost most of prop power

Well, I changed the propeller and took the boat to the lake. While floating on the trailer, it would not pull itself off the trailer in reverse, so no thrust at all.

The last time I used this second prop, it moved the boat well, just not as good as the stainless. So, I guess I conclude that the problem is in the upper unit or at the coupler.

Shopping for repair service now is a real pain in Sacramento. All the shops appear to be 2 - 3 weeks out before they can diagnose this one.

I would pull the stern drive, but that accomplishes nothing if I cannot also raise the engine to replace the coupler.

Note: I could not see the coupler from above the engine. I see the drive shaft spining but no coupler so I do not understand how to do the red line marking of the coupler and the shaft.

Thanks to all for the info. It was helpful.

 

[Don S]

Re: Lost most of prop power

Note: I could not see the coupler from above the engine. I see the drive shaft spining but no coupler so I do not understand how to do the red line marking of the coupler and the shaft.

Mirrors, flashlights, and working by feel only.
That is how professional marine techs work 90% of the time.
We are't supernatural, we just learn to deal with our enviornment.

PS: Blood letting on a job is SOP. If you don't bleed on your work, you did something either too slow, or improperly.

 

[dockwrecker]

Re: Lost most of prop power

Classic dead coupler. The smoke is burning rubber.

 

[Bondo]

Re: Lost most of prop power

PS: Blood letting on a job is SOP. If you don't bleed on your work, you did something either too slow, or improperly.

Ayuh,..... Ya got That Right,....

I would pull the stern drive, but that accomplishes nothing if I cannot also raise the engine to replace the coupler.

Huh,..?? It's called Diagnostics,... Seeing exactly What's Broken....

 

[deandec]

Re: Lost most of prop power

Well, since I cannot get a pro rapidly, I will attempt to pull the sterndrive. I have not done that before but do have the instructions and have read a bit about other people's problems.

Will build a stand to assist this old body in the effort.

In my research, folks seem to have a problem with resistance when turning the prop shaft to re-install the stern drive while in forward gear.

My prop spins easily in forward gear or neutral with the engine off. Is this a symptom of something?

 

[dockwrecker]

Re: Lost most of prop power

You can pull the sterndrive to look at the coupler, but I don't think you can change it from there. Mine had to be done by pulling the motor. Bond-o??? Yes? No?

 

[Bondo]

Re: Lost most of prop power

Well, since I cannot get a pro rapidly, I will attempt to pull the sterndrive. I have not done that before but do have the instructions and have read a bit about other people's problems.

Will build a stand to assist this old body in the effort.

In my research, folks seem to have a problem with resistance when turning the prop shaft to re-install the stern drive while in forward gear.

My prop spins easily in forward gear or neutral with the engine off. Is this a symptom of something?

Ayuh,... The drive weighs about 80lbs...
By adjustin' the trailer jack, you may be able to just lean, tilt,+ otherwise not really Lift it...

You've gotta start by Drainin' the oil from the drive,.. Look for Metal...
The lack of resistence could mean it's drive related,+ Not the Coupler....
(Yes, the coupler is mounted to the aft end of the Motor)

"It's called Diagnostics",.... 1 step at a time......

 

[deandec]

Re: Lost most of prop power

Ok, a diversion here. I just painted the line on the shaft and coupler.

They do spin together when not under load as does the propeller.

With the boat floating above the boat trailer in the lake, we applied forward and reverse gears and tried to move the boat at about 2,000 Rpm.

There was no thrust in either direction.

The paint lines were still lined up on the coupler and the shaft.

The propeller is not the one that was in use when the problem originated.

So, now it might be a problem inside the outdrive?

I did drain the outdrive oil. It appears normal color and no contaminants. I used a magnet in the oil and retrieved no metal.

 

[Bondo]

Re: Lost most of prop power

So, now it might be a problem inside the outdrive?

I did drain the outdrive oil. It appears normal color and no contaminants. I used a magnet in the oil and retrieved no metal.

Ayuh,.... Keep diggin',... It's only 6, 8 nuts,+ a 6 dollar gasket,... Pull the drive....

 

[Glastron_V210]

Re: Lost most of prop power

It could be inside the drive, but probably not. I'd guess you would have heard some crunching of gears if this had been the case.

It is very likely the coupler. Pull the outdrive, then remove the engine.

In neutral the prop should spin very freely, and is indicitave of nothing.

The drive is easy to get off. If you are not physically fit ask for help. I do the alpha on and off by myself by using blocks uder the skeg.

There are many posts you can search if you run into trouble.

Good luck, hope it's just the coupler. Getting the engine out is not usually too bad (1-2 days). The manuals are in the adults only section...just follow along.

Chay

 

[Cptkid570]

Re: Lost most of prop power

Well, I would make sure that it's the coupler before I pulled the engine. If it still spun and your line is still right, I wouldn't think it's the coupler.

Can you pull off the very top cap on your outdrive so that you can see the upper gears? Have you tried putting it in gear and spinning the prop by hand?

You may have stripped the upper gears in your outdrive..

Here is a picture of the inside of my upper gears of my outdrive when I stripped mine.. You can't see in there real well, but if you can see the smooth part, that was not supposed to be smooth..

 

[dirtyoldman]

Re: Lost most of prop power

My prop spins easily in forward gear or neutral with the engine off. Is this a symptom of something?

I find this comment interesting. It should spin freely in neutral, one way in forward, and the opposite way in reverse. If not and your coupler isn't moving it's internal to the drive.