Sheared Alternator Shaft

RSlater · 08-17-2005, 07:59 AM

Just driving along at about 2500 rpm in 2nd when she decided to detonate.

Credit Drago for the Photos
Sorry guys Wheels declined on the photo shoot

Jadams1 · Jadams1's Garage

WOW, that must have sounded bad when it let go.

RSlater · 08-17-2005, 09:05 AM

Definantely woke me up as I was out for a nice leisurely drive around the lake. Sounded like a massive backfire.

Drago · Drago's Garage

That'll buff right out.

Oh, and I hear you can just use a little dab of JB Weld to put those blades back on.

rdane · rdane's Garage

Musta been the heat..

MysticLlama · 08-17-2005, 09:33 AM

Wow, that is crazy how it just trashed the fan like that. Yikes.

TerryH · TerryH's Garage

wow... pretty catastrophic from an alternator's point of view. Must have some kind of major stress on the alt shaft for it to shear off like that.

Perhaps the front alt bearing has been seized/dry for a while causing metal fatigue from heat. That would be the load bearing area that would be stressed by the belts.

RSlater · 08-17-2005, 10:08 AM

Quote:

Originally posted by rdane
Musta been the heat..

Do ya think!!

When I told JW about it he said he hadn't seen that before.
But he has since talked to gerber and they've seen it a couple of times

Drago · Drago's Garage

Has JW commented on the lower pulley damage yet?

RSlater · 08-17-2005, 10:27 AM

Quote:

Originally posted by Drago
Has JW commented on the lower pulley damage yet?

May be repairable.

Drago · Drago's Garage

Quote:

Originally posted by TerryH
Perhaps the front alt bearing has been seized/dry for a while causing metal fatigue from heat. That would be the load bearing area that would be stressed by the belts.

The alternator shaft spins freely.

TerryH · TerryH's Garage

yeah, I don't see any blueing on the broken shaft.

Perhaps the broken alt shaft is a result rather than a cause. If one of your fins suddenly broke and went around the pulley causing the belt to overstress the shaft...... we'd better call Columbo on this one. Ahh..... just one more thing, sir.

alan911 · 08-17-2005, 04:14 PM

Oh the Humanity.!!!!!!!!!!!!!!!!!!!! Worse than the Hindeburg....

Jubbie · 08-17-2005, 05:31 PM

Lucky the fan shroud and the belt held the fan for a bit, lest you have a new air opening in your hood.

Damn, sorry to see that. Was the belt set right?

RSlater · 08-18-2005, 05:23 AM

Quote:

Originally posted by Jubbie
Lucky the fan shroud and the belt held the fan for a bit, lest you have a new air opening in your hood.

Damn, sorry to see that. Was the belt set right?

Lucky is right since the entire deck lid and tail are carbon fiber.

Yes. The belts where recently adjusted.

Drago · Drago's Garage

Quote:

Originally posted by RSlater
...since the entire deck lid and tail are carbon fiber.

Toot, toot.

Walt Fricke · 08-18-2005, 08:50 AM

The photos don't have the fracture surface in as sharp a focus as some of the other parts, but if what you see is what there is, this looks like a sudden failure. Typical shear or bending failures of rod-like parts (bolts, axles, shafts) show a kind of "waves on a beach" or "half a tree-rings" which look like they start at a point on the circumference of the shaft, and then have semi circular rings getting larger and deeper into the shaft as successive stress cycles broke a bit more and a bit more, etc. Sometimes you can see rust on the outer and earlier parts of this growing fracture. Sometimes those parts are polished. Then there is a pebbly, grainy area which all looks the same as far as surface characteristics are concerned. That is the area which finally just broke all at once, rather than bit by bit.

If so, that would be one clue supporting the "fin broke first" hypothesis. Still, that is a thick steel shaft and some of us know from trying to tug on the fins how weak they are.

Walt Fricke

Drago · Drago's Garage

Quote:

Originally posted by Walt Fricke
The photos don't have the fracture surface in as sharp a focus as some of the other parts, but if what you see is what there is, this looks like a sudden failure...

....Then there is a pebbly, grainy area which all looks the same as far as surface characteristics are concerned. That is the area which finally just broke all at once, rather than bit by bit.

Yeah, sorry about that picture coming out blurry...it looked more focused on the tiny little preview screen on the camera.

What your describing is exactly how the break looks...very uniform and grainy. Still, I have a hard time thinking that one weak blade breaking off would cause a ~5/8 inch steel shaft to fail.

osidak · 08-18-2005, 09:57 AM

Wow - besides being expensive that just looks spooky

Early_S_Man · 08-18-2005, 10:11 AM

Quote:

What your describing is exactly how the break looks...very uniform and grainy. Still, I have a hard time thinking that one weak blade breaking off would cause a ~5/8 inch steel shaft to fail.

It wasn't the blade breaking that caused the sudden load on that shaft ... it was the sudden decceleration caused by the fan assembly jammed in the housing! There isn't enough room for loose fan blade bits, rotating fan, and housing to coexist in the same space ... there had to be some serious bending and shear moments involved when the fan came to a sudden halt! The inertia of the alternator rotor/field windings was overwhelming ... compared to the fan and shaft resisting force ...