Crank Pulley ripped off!

[Brave Salmon]

My crank pulley somehow got ripped off the balancer. Sbf, 3 bolt pulley with 2000 miles. Bolts were tight and no other damage is apparent. Motor still runs fine. I can replace the pulley but what caused the failure. I was cruising at 35mph with no strain on anything. Here's a picture. Suggestions are welcome.152575

[RoadRacer]

No idea to the root cause, but I've had the same exact thing happen to me on a SBF. Mine was at the race track when it happened, but still quite bizarre.

You may never know, I put mine down to a manufacturing defect.. I did over 50,000 miles on its replacement!

[33fromSD]

I've seen this before too twice on SBFs. The first one the guy it happened too did not have the crank pulley fully seated squarely on the crank so when the engine was running, the off kilter crank pulley turning other pulleys on the engine caused the crank pulley to shatter due to a wobble.

The 2nd one was a buddy I knew grabbed an old 289 out of the junk yard which looked like a solid rusted pile of junk, but it ran though, the problem was the crank pulled was so rusted to the point that after a few hundred miles a stress fracture formed in the pulley and in time it broke away. Made one hell of a noise running down the interstate.

Jim

[J R Jones]

The drive pulley is mounted to the inside of the harmonic balancer. That implies that the crank is vibrating and the balancer ring damps it out.
Your fracture looks like a fatigue failure, not a load failure. If you examine the raw edges you may find dark (older) fractures and clean (recent) fracture.
This could be an old part beyond it's service life, or your damper does not match your crank balance. Your engine balancer may have an opinion.
jim

[Bob Cowan]

Looks like 1-2 loose bolts caused a wobble at speed. Some balancers have blind holes. And some have holes that are tapped all the way through, but over the years the unused threads get rusted. If you use a bolt that's just a smidgen too long, you can torque it down to specs, but it won't provide proper clamping force.

[GoDadGo]

I've Never Seen This Kind Of Pulley Falure Before!
Just understand that there are a lot of things I've never seen before.

[first time builder]

I agree with Bob To long of bolts or rust in threads cause an improper "tighten" feeling.

[NAZ]

I've Never Seen This Kind Of Pulley Falure Before!
Just understand that there are a lot of things I've never seen before.

That's because you don't have that problem with a Chevy.

[NAZ]

Looks like 1-2 loose bolts caused a wobble at speed. Some balancers have blind holes. And some have holes that are tapped all the way through, but over the years the unused threads get rusted. If you use a bolt that's just a smidgen too long, you can torque it down to specs, but it won't provide proper clamping force.

Sounds as if this is a likely cause. Easy enough to check if the cap screws that held it in place are still there. Simply screw them in the blind holes without a washer and see if they bottom out with more gap than required to apply a clamp load to the pulley.

[J R Jones]

NAZ, There is that, or, the pulley fragments left on the balancer hub would be held tight, or not. Sometimes problems are not dramatic.

I admit to not torquing every fastener, out of convenience or lazyness. Experience and awareness has provided a muscle memory of a fastener clamping the surfaces, and then stretching to it's "happy state". Like Zen. Actually that is "torque and turn" before it was popular.
I have actually watched more than one hack, pull a fastener tight, then give the wrench an arbitrary jerk, "just to be safe".
The SCCA did a survey/analysis of club car failures at the track and found the vast majority root cause is fasteners.
jim

[Brave Salmon]

All three bolts were still in place holding down the fragments from the pulley. The stamped steel pulley was comprised of two thicknesses of steel held with rivets. Ford OEM used a bizillion of these in fords for years before going to 4 bolt pulleys in the mid 70s. All bolt holes are through holes and the bolts at 1" are short enough to not pass through to the back of the balancer which is 1" thick. Its not a clamping force issue. I suspect that the pulley was defective from the factory. I had checked the timing a month ago and would have noticed any wobble at that point. There was no pulley or damper wobble at all. I've installed a new pulley today and Ill see how it works out over time. Torqued the 3 bolts to 40Lbs/ft and the water pumps 4 bolts to 25lbs/ft. Thanks for the assist gang.

[J R Jones]

You opening comments include the statement of 2000 miles service life. Was this a new part, or a used part with total mileage unknown?
As you stated, this part has been made in big numbers. The technology (steel stamping) is a mature process and creates reliable parts.
A Ford made, or sourced part would not fail at 2000 miles. Was this pulley a reproduction created off-shore?

What Ford engine is this? Were the harmonic balancer and flywheel part of the engine balance?
If you do not get to the bottom of this, you should zero your "B" trip odometer and stop at 1990 miles for an inspection.
jim

[J R Jones]

Salmon, Two more troubleshoots come to mind.
The harmonic balancer also has to be bolted-on correctly. You should check the fastener torque securing it to the crankshaft.
The composition of the balancer is a cast iron hub pressed into and isolated from the outer ring by a rubber isolating band. The outer ring should not have run-out as it turns and nothing should interfere with the isolating feature.
For instance the belt pulley should contact the hub segment only and not come in contact with the outer ring.

If there is a defect in the part, it could be dimensional like my interference comment above, or a material defect which is more likely with an offshore source.
jim