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Impulse 9 Shattered Shaft

4955 Views 11 Replies 9 Participants Last post by  ruckus
I had a guy custom make a coupler/adapter for my MG conversion. Installed it and got a loud vibration and was able to observe a wobble in the coupler. I sent it back and he corrected the wobble. Once installed I got less of a vibration/more of a loud buzz.

I was an idiot and assumed since the coupler no longer wobbled that the buzz must be coming from my trans. I drove it for three months like that and finally decided to pull the motor/trans to see if I could figure out the buzz. Upon separating the trans and motor the coupler fell off along with pieces of the motor shaft. The clutch plate bolted to the coupler also had cracks.

a) Anyone know a good source for Warp motor repair parts? I assume the drive end bearing is also toast, although the motor runs pretty smoothly with no load.

b) Has anyone else had a similar failure? If so, did you determine a cause?

c) Any educated guesses as to a cause for the failure (other than me being an idiot)?

All opinions welcome.

Thanks!
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Is the shaft split into pieces from the edge to the center hole? I've suspected that the Warp motors had to large a hole for the pilot bearing. A 0.687 inch hole in the center of a 1.125 inch shaft would be fine (0.219 inch wall) but the 1/4 inch keyway creates a thin area and a couple of sharp corners.
 

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I had a guy custom make a coupler/adapter for my MG conversion. Installed it and got a loud vibration and was able to observe a wobble in the coupler. I sent it back and he corrected the wobble. Once installed I got less of a vibration/more of a loud buzz.

I was an idiot and assumed since the coupler no longer wobbled that the buzz must be coming from my trans. I drove it for three months like that and finally decided to pull the motor/trans to see if I could figure out the buzz. Upon separating the trans and motor the coupler fell off along with pieces of the motor shaft. The clutch plate bolted to the coupler also had cracks.

a) Anyone know a good source for Warp motor repair parts? I assume the drive end bearing is also toast, although the motor runs pretty smoothly with no load.

b) Has anyone else had a similar failure? If so, did you determine a cause?

c) Any educated guesses as to a cause for the failure (other than me being an idiot)?

All opinions welcome.

Thanks!
Do you have any pictures of the shaft, coupler, and adapter? Did you check to make sure the motor shaft and transmission shaft were concentric? Wild guess would be they weren't concentric which puts large stresses during rotation that will fatigue the connection quickly.
 

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Discussion Starter · #4 ·
Is the shaft split into pieces from the edge to the center hole? I've suspected that the Warp motors had to large a hole for the pilot bearing. A 0.687 inch hole in the center of a 1.125 inch shaft would be fine (0.219 inch wall) but the 1/4 inch keyway creates a thin area and a couple of sharp corners.
The first inch of the shaft was either powdered or fell out of the end of the coupler in pieces when I separated the motor and trans. The keyway was gone from the remainder of the shaft.
 

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There is an axiom in incident investigation......

"The problem is always closest to the area of most damage."

Using this as a guide, My guess is that the clutch disk area was out of balance. It wobbled more than farther up the motor shaft where the damage was less.

Yes, the weak spot in the motor shaft is at the end at the two square cuts in the keyway slot.

The key is in pieces or missing because it was ground up or slung out.

Bench test any new ones.....before installation.

The motor shaft can be welded up and machined back to new if necessary. Easy.

Miz
 

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Discussion Starter · #6 ·
Do you have any pictures of the shaft, coupler, and adapter? Did you check to make sure the motor shaft and transmission shaft were concentric? Wild guess would be they weren't concentric which puts large stresses during rotation that will fatigue the connection quickly.
Yeah, I corresponded with Netgain today looking for parts. They asked for pics and that was their conclusion too. "Severe misalignment!" was the exact diagnosis. Everything slid together nicely when I put it all together. There wasn't a misalignment I could see. Sure did wreck the motor though. It needs a new armature and bearings as you can see.
 

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Discussion Starter · #7 ·
There is an axiom in incident investigation......

"The problem is always closest to the area of most damage."

Using this as a guide, My guess is that the clutch disk area was out of balance. It wobbled more than farther up the motor shaft where the damage was less.

Yes, the weak spot in the motor shaft is at the end at the two square cuts in the keyway slot.

The key is in pieces or missing because it was ground up or slung out.

Bench test any new ones.....before installation.

The motor shaft can be welded up and machined back to new. Easy.

Miz
Thanks, Miz. I'll definitely wring out the next one before I drive with it.
 

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"Everything slid together nicely when I put it all together."
Alarm bells ringing!
The coupling should be an interference (shrink) fit on the shaft, or at the very least a "taperlock" type coupling

The failure was almost certainly misalignment / imbalance. The shaft alignment between the motor and the gearbox needs to be no further out than 0.002" Did your coupler use a brass bush in the motor shaft to support the spigot bearing landing on the gearbox shaft?
There is no more than 0.0005" runout permissible on the coupling outside diameter.

I am assuming this was a clutchless conversion. If you use a clutch and flywheel then the whole assembly should be dynamically balanced and this isn't a DIY job.

"There wasn't a misalignment I could see."
The accuracy you need to be working to requires the use of a dial gauge, eyeballing won't do.



Derek
 

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Yeah, I corresponded with Netgain today looking for parts. They asked for pics and that was their conclusion too. "Severe misalignment!" was the exact diagnosis. Everything slid together nicely when I put it all together. There wasn't a misalignment I could see. Sure did wreck the motor though. It needs a new armature and bearings as you can see.
'
'Unfortunate and impressive failure! Can someone explain what we're looking at? It looks like a cylinder(with threads inside) within a cylinder. Maybe before and after pics would help.
 

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Does anyone use that bore for a pilot?

i don't see how and so you wonder why is it even in there? Obviously it a cleaance bore for a socket to tighten a 5/16-18 bolt, but what are you going to bolt to the shaft that deep in?

It looks like a sudden overload fracture, not a fatigue failure. The fracture zone is in the plane of the square-bottom cut bore at the top of the threads. You can see where a drill bit was run in to drill out most of the material, then a boring bar was used to square up the sides and bottom. Very little fillet at the bottom (radius on the tool bit) creates a high stress region. Add in some rust (why is there rust on that surface?) and the margins are reduced. Add in some mass imbalance, even with perfect alignment, and the loads go way up. High loads, lower margins, recipe for failure.

It must be a design from some other application. The shaft is only 1.5 inches long and half of that is bored out--doesn't seem to leave much to grab on to if you are planning to run high torques, but i haven't run the numbers...

p.s. What you are looking at the Drive End of the motor, there is a bearing pressed into the end bell, then there is about 3/4" stub of what's left of the motor shaft, there is another 3/4" of the shaft missing plus about 1/3 of the circumference in the threaded portion.
 

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Looking at the pic , the shaft inside a shaft appearance appears to correspond to the washer diameter. Perhaps excessive torque on the end bolt?:confused:
I think the washer "supported" the shaft, keeping it intact. The key to this riddle is the vibration. It could have been from any of the parts involved (clutch, coupler, adapter). The fact that the coupler guy screwed up the first "try" isn't reassuring.

I believe the technical term is "rabbiting". A slight misalignment along with a tiny bit of slop. The results are ugly. I'm fingering the fit of the coupler. Too loose.

Sorry for your loss. :(
 
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