Broken prop shaft

phatsat67 wrote: Ken, is that coupler side splined too? MC has used splines for propellers for a while now.

The ones I've seen had splines on both ends, but I don't know if they all are

Riley wrote: Just curious, is everyone that has bought one of these using a torque wrench to lock the shaft into the taper? Does that matter?

More than likely a 10" crescent and a piece of pipe

Ken, is that coupler side splined too? MC has used splines for propellers for a while now.

Not to beat this to death but I stumbled onto the patent info, regarding the coupler taper it appears the steep taper was deliberate to facilitate "easy" removal and decrease man hours required.

From the patent application
"A coupling receives a steeply tapered end of a propellor shaft and is secured thereto with a lock nut held in place with a set screw. A housing taper is steeper than known locking tapers to facilitate housing removal. The housing is internally threaded to receive an extractor element which, after lock nut removal, is screwed into the housing for abutment with the end of the propellor shaft with continued advancement of the extractor element resulting in housing separation from the shaft."

full link

I used to be in the steering wheel business. We sold steering wheels that fit onto splines and tapered steering column shafts with a hub mated to the wheel with Huck fasteners. Never had issues with fit.

Doesn't Mastercraft use splines/taper on their propellor to shaft engagement?

As a ranking ameteur who never even aligned a prop shaft, let alone replace one with an ARE, but who does have some mechanical aptitude, is there a reason why splines aren't used in conjunction with the taper instead of a keyway? Square corners are bad enough but reduction in cross-section to 7/8" seems to point to using a larger shaft diameter if the keyway is going to stay. I know that's impractical at this point.

Splines sure don't fail like that keyway. They're more expensive to machine but there must be another reason that I'm missing

As I am sure several know, but some may not, the ripples indicate crack growth. The closer ones point to where it started and the ones farther apart indicate where it was speeding up due to the reduced cross section. The big chunk in the middle is where it finally broke. We have known for some time that sharp corners are bad, but surprisingly they still get left. That was my first thought.

MrMcD wrote: I installed a new ARE shaft, now has 50 hours on it but this thread has me concerned. I know I lapped the prop well but do not remember lapping the coupler end. Maybe time to tackle that job? Mine was installed in 2014 is that the new or old version? Sorry about your troubles but thanks for pointing out an issue to be addressed! Mark

Me too. We've got about 50 hours on ours. I'd be pretty disappointed if it broke. If I remember right, they required the nut be torqued to 60 lbs?

I installed a new ARE shaft, now has 50 hours on it but this thread has me concerned.
I know I lapped the prop well but do not remember lapping the coupler end.
Maybe time to tackle that job? Mine was installed in 2014 is that the new or old version?
Sorry about your troubles but thanks for pointing out an issue to be addressed!
Mark

phatsat67 wrote: Do you have a good shop locally that could machine lap the coupler than face it after it was installed on the shaft?

I've never thought about it that way, but really would make sense. When you add up the cost of a shaft, lost time, and possible cost of a prop, it would be good insurance against alignment issues.

Dang Alan, that sucks. I guess I was too hard on the throttle at Quinners. (thanks for letting me run it around again).

Joe is the shaft expert. Kev has had Duane in indy make some pretty neat stuff all around. Would be a great option if something else breaks. Do you have a good shop locally that could machine lap the coupler than face it after it was installed on the shaft?

I've always wondered how far off the coupler faces are. I try and do my alignment by moving the shaft into all 4 possible positions once my initial alignment is set to check coupler face and shaft runout.

Hopefully this doesn't break. We have put about 200 hours on my brothers ARE in the 89. Extra 1.23 torque and slightly less HP than the Hemi.

Pete, if they sold those shafts without a key people would be spinning them in the taper more often than not. I'd guess that 1 in 20 of their customers would take the time to lap the shaft into the taper, maybe less. I think it's just practical for inboard shafts to have a key, but some engineering has to be put into the taper and key design, as it sounds like Joe indicated to one of the suppliers.

Hollywood wrote: The keyway on the new Elbert's coupler is long and square (1/4"?) just like the prop end.

Well that makes sense, glad they could learn from my field test results over the last 5 years. Do they put a pin in the key to keep it from sliding like General Propeller?

JoeinNY wrote: . That taper is short, and that keyway is deep.   .

I agree the keyway seems far too deep and is exactly where mine broke. I'd hate to think it couldn't handle a sub 300 hp motor but the fact that they have changed their taper means something. I wonder if the keyway has changed as well. If it wasn't July I would take more time and go a different route. I'm probably setting myself up for another hit,

Guess I'll look into general prop over the winter.

So after some thought I'm going to lap the new shaft to the coupler and then put it on some blocks and check the coupler face runout before installing it. I'll have it machined if need be. Realign it and then check it again with the boat in the water and see where it is.

Pete, to your comment, I was told yesterday that ARE did change the taper of the coupler end on their newer shafts. he didn't say why, only that it was an improvement. I had to stay with the old taper because the coupler was custom made to the old taper spec and I'd have to pull the mating piece off the transmission and send it to them again and I don't want to loose the time and money it cost for a new one. I'll get it lined up perfect and take my chances. It should be fine if I make sure it's trued up correctly.