Broken prop shaft

So the Hurricane continues to win these little battles by cutting another day short this weekend. After running really well the weekend before at Quinners party we felt comfortable enough to take it to the river and put some hours on it. Everyone that drove or rode in the boat that weekend commented on how smooth it was.

We ran about 20 miles up river, did some socializing then turned around to head back. About half way I dropped into idle to ride out some big rollers and when I dropped it back in gear it gave a big clunk. I knew it was broke good so I just opened the hatch to make sure we weren't sinking.

Prop shaft snapped right at the coupler. Luckily it was busy and a couple of guys on a pontoon went out of their way to tow us about a mile to the nearest launch and then even gave me a ride to retrieve our trailer at our put in site which was still about 6 miles away.

Looking at the shaft it appears there has been a fracture there for a while so this is probably an issue that started a while ago and finally gave up. Question is why does an ARE shaft with probably 100 hours on it break. I've been meticulous with alignment on this boat, checking it probably more times than I have ever done on all my other boats combined. There's never been any change every time I checked.

At lunch to day I stopped by the machine shop and had them press the broken stub out of the coupler. There's evidence there that the taper never really seated very well into the coupler which was custom made by ARE to fit the Hemi. I confess I never did lap the coupler end of the shaft so I guess had I been more attentive I may have been able to avoid this if that's really why it broke.

Here's some photos, if anyone has anything to add I'd appreciate any advice. New shaft is already on it's way, summer is too short.



left side is real dark and apparently been cracked for a while, also the dark center spot looks like it migrated from the keyway. but again why? out of alignment?, don't think so. Was the shaft never seated properly in the coupler and moving around a bit, I'll tell you we had to put the coupler in a press to get the stub out so it certainly seated partially.


The dark area is the beginning of the taper


You can see where the narrow part of the taper is seated well and the wider part is not.

So anyway we made it back to safety with the help of some good samaritans but I would sure like to know what happened so I can learn from it. Installation error, bad taper fit, is the motor possibly moving under load, sure doesn't appear to be. One thing I have never done is check the alignment with the boat sitting in the water, it's always been on the trailer. Worth a look once I get it back together.

TRBenj wrote: Damn that's a ball buster. If the coupler wasn't seated fully on the taper, could you have been aligning to a coupler face that wasn't perpendicular to the shaft? (Can't see the pics btw).

that's one of my theories Tim.

Sorry to hear that Alan. Glad you made it in safe. And on top of the water.
Really enjoyed one of your last videos (FB.....I think). She was sure running strong and looking great.
She will be back!

Alan,
I agree with Tim's theory regarding alignment to the face of the coupling and if the shaft wasn't seated fully then there sure would have been a very slight out of parallel shaft. On the ARE's I've installed, I have lapped them and did find that the tapers between the coupling and shaft were off. The other issue is the taper is very short and steep so it's harder to fully seat. Keep moving forward. One of these days I'll get a ride!

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.

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.

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?

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.

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.

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.

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

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?

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.

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

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?