Stripped driveshaft - Why?

[yonipainting]

I have recently bought a bass boat with 150 Johnson Looper. The lower unit was dropped down to show a stripped driveshaft.
I didn't buy a new or used driveshaft. Friend of mine claimed he could repair it. He welded the material on splines, machined it back to the right diameter, and the splines were machined back on. All this was done at the professional machine shop.
The driveshaft fit perfectly in the crank. The lower unit was re-packed (there was a lot of water in there) and re-sealed and installed back on.
I drove the motor (on 3/4 of power) for 10-15 minutes and driveshaft spun again.
Not sure if it is the driveshaft or the crankshaft yet (have to drop the lower unit).
Now, the question is why was the driveshaft stripped at the first place, what are the possible reasons for that?
If I drop the lower unit, find a stripped driveshaft, inspect the crankshaft and conclude that splines up there are good, what do i do? Do i put my suspicion on fixing of the driveshaft (it was not put through any thermal treatment) , do I look for the original part, or do I just give up on the motor because there is something going on with the crankshaft bearings maybe?

Thanks

 

[GA_Boater]

Bad, rusty, notchy bearings in the lower unit due to water is my guess. I would also look at the matching splines in the crank to make sure they are solid.

 

[Bosunsmate]

I suppose you have ruled out your prop now being the cause (spun in hub)
Id be inspecting the gearbox oil and magnetic pick up screw if that motor has one.
To ruin those splines you normally need a sudden jolt such as a gear in the LU jamming up

 

[kbait]

Or running over the too-long bow line (just replaced a customers drive shaft for that issue.. snapped at pinion gear in gearcase).

 

[yonipainting]

I suppose you have ruled out your prop now being the cause (spun)
Id be inspecting the gearbox oil and magnetic pick up screw if that motor has one.
To ruin those splines you normally need a sudden jolt such as a gear in the LU jamming up

Yes, spun prop is ruled out do to a fact that there is no water being pumped out

 

[bonz_d]

Had the same issue with a 1988 70hp Evinrude. Driveshaft was also stuck into the crank because it had spun. When I finally got it out there were basically no spines left on the driveshaft and upon further inspection the splines inside the crank were wiped out also. Whe I also got the shaft out I found that there was no o ring at the top of the shaft to water intrusion out. Was told by a number of people that the missing o ring is the major cause of driveshaft failure at the splines.

 

[Chris1956]

Gee, what would happen if the gearcase was installed, and the driveshaft and crankshaft splines were not mated, but forced together? Sounds like a possible scenario as well.

 

[Tim Frank]

Yes, spun prop is ruled out do to a fact that there is no water being pumped out

Can you explain what you mean?
Not sure what connection you can make between pumping out water and a spun prop hub.

 

[yonipainting]

Can you explain what you mean?
Not sure what connection you can make between pumping out water and a spun prop hub.

Well, as far as I understand (and I am not claiming to be an expert by no means), If there is no water being pumped through the motor, that is a sign of impeller not turning, and in turn a sign of lost connection between the crank and drive shaft ( that is the explanation I got from the mechanic even though it is not making a complete sense to me as am writing all this)
I can also turn the prop by my hands when in gear and flywheel is not turning.

 

[Tim Frank]

Two different things entirely.
Do a search in here on "spun hub". There are good explanations and a procedure for checking.

 

[bonz_d]

Two different things entirely.
Do a search in here on "spun hub". There are good explanations and a procedure for checking.

If the splines on the driveshaft were wiped out there is a better than good chance that the splines inside the crankshaft were also. Then if the driveshaft was repaired/replaced w/o reparing the crankshaft then there still would not be a proper fit between the 2 and it would just strip it out again. There is a great load on that joint and won't take much to destroy it again.

I think it would be wise to pull that LU and recheck that driveshaft and yes I understand that it will be difficult to check the crank.

 

[Tim Frank]

Sure.....but it's a heck of a lot easier to check the hub first..... just in case

 

[bonz_d]

Maybe he should just put it on muffs, run it in gear and see if anything turns.