So, a couple weekends ago I installed an AFR and went out to do some tests. Yes, my car was running rich as most people have said recently... more on that later. I'm cruising along the highway, paying very close attention to my new AFR gauge and little attention to the CHT gauge.

I pull off the highway and things smelled a bit hot - after all it was 90 degrees and sunny - then I glanced over at the CHT - over 450!!! I've never seen temps like that so I pull over immediately and let it cool. Fired up no prob but the temps climbed quickly back into the high 300's within a few minutes. After reaching around (and googling a bit) I reached back and felt the belt and cooling fan totally loose.

I called my insurance company and got her towed back to the house. Due to vacation and work, it took me two weeks to finally pull the engine. Here are the pictures:
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How could this happen?

How could a 40 year old part that has gone through thousands of heat cycles fail?

There is no evidence of a woodruff key (N 012 708 2) in those pics.

I must have been running for a while without it, and finally the impeller hub wiggled loose and OVER that fan bolt???....
Missing large washer?

I am guessing that the bolt was not like in the pics when found, but laying in the fan housing...

Stu

When this occurs the hub key becomes ejected because the key way in the crankshaft is compromised and will no longer hold the key in place(especially at WOT with centrifugal force being high).

Generally this requires complete disassembly to correct as the morse taper and keyway of the crankshaft are permanently damaged and will not hold the hub securely in place.

With CHTs hitting 450 it probably has seen other compromises as well, even if it only saw those temps for a few minutes or even a few seconds under load.

I did the original engine assembly including the fan and housing about 3 years ago...

And I took it apart myself. The bolts are untouched other than a quick wipe down. I saw no key and no evidence of the key anywhere. Are there any other parts not shown in the pics that are typical?

Thanks,

Steve

The key is probably laying atop the cylinders somewhere. They typically discharge at a high rate of speed, bounce around and are delivered to the top of the engine with the cooling air charge.

I emailed you a couple of tricks to try to bail yourself out of trouble :-)

Yes..........A big fat washer that hold the hub to the crank.

The bolt that is in the end of the crankshaft is supposed to have a thick large washer and hold the fan hub onto the crank. Since it looks like the fan is still bolted to the hub, it seems the bolt out of the crank is/was not doing anything (holding the hub and fan to the crank )

The big washer is probably laying atop the cylinder tins too. If the parts were ejected at 3-4,000 RPM they will probably never will be found.

I once had this happen on the dyno when a center bolt broke in half at 5K RPM on a test engine. The fan flew off and the key ejected and pierced through the ceiling of the dyno room after it exploded a fluorescent light bulb. The ceiling had acoustic dampening material as one layer, then a sheet of 3/8" plywood above that.

The fan and hub assembly ran up the wall in the corner of the room and jammed inside the exhaust fan for the test cell. We finally found the big fat washer 8 years later when I re-plumbed the test cell, it was jammed between the floor and the wall and was folded in half.

Hey Jake!

Steve are the photos taken as discovered? Did you put the crank bolt back in the end of the crank or is that how you found it?

I hate to second guess Jake but it Looks like the bolt was installed during your rebuild without the thick washer to me.

I did not put the bolt back. Give me a few minutes - i will pull the bolt and see if part of the washer is still there

Also was the bolt still tight when you just pulled it?

I would say, if you find the parts, to clean it up and bolt it back together again. Then try to wiggle the fan, and if it moves you know you're hosed.

If not, run it--but save for a new engine, because you have pretty decent odds of this one not lasting very long. And it may blow spectacularly, which would be cool to those of us who don't have to suffer through it.

If the keyway is messed up, the crank and fan hub are both toast. At that point you need a new crank, and if you're replacing that you're doing a full-on rebuild anyway.

Jake may know ways to save it; I don't know any that I'd trust for long, but he knows a heck of a lot more than I do.

Or you may get lucky, and it will run once it's together again for a good while.

--DD

The center bolt was tight, very tight. Plenty of red loctite on there as well. The fan bolts connecting to hub were all tight as well. No sign of the key anywhere - or the large washer, other than the one between the hub and fan. See pics:
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If the hub came off with the bolt still in place, you must have forgot the washer that goes between the hub and the bolt, or somehow the big assed washer came apart. If you did forget that washer, or used a smaller washer, you are very lucky to have seen 3 years without it.

I would pull the seal and replace it. The woodruff key may be inside the lip of the seal. I would replace the fan hub, get a new key and thick washer that belongs on the center bolt and put it back together. Oh and change the cooked oil.

But as Dave posted you may want to think about rebuilding another engine. The heat cycles may have caused the worst of the damage. Who knows you may get lucky.

I am startingvtonthink that the thick washer was also left out of the equation, Steve. I thought that maybe you had retreaded the bolt yourself, after the fan "fell off".

The odd thing is the OD of the bolt is just a tad smaller than the ID of the hub and I cannot see how it stayed together for more than a few minutes without the load bearing washer.

The key could be tucked behind the crank seal....

My observations: CAREFULLY inspect the nose of the crank and the inside of the hub. Both MUST be smooth over the complete contact area of the taper. Good used hubs are available. In the second closeup of your hub, the surface appears to be trashed. Chingered up cranks require replacement. While a few little divots may be OK, ANY raised spots can be fatal to the fit. Make sure the Woodruff key fits tightly in the slot. If it's just a tiny bit loose, you "might" get away with a good cleaning and some green Loctite. If the key is undamaged and the fit is obviously loose, the crankshaft is history. The key mostly serves to locate the hub. It doesn't really hold it from spinning; the taper does that. Get the correct washer. It will NOT be available at your FLAPS or HD. I can't tell if the bolt you have is correct, but it should have little teeth on the contact surface of the flange, making it somewhat self locking. You shouldn't need thread locking compound for this fastener.

Get a new seal AND o-ring.

Good luck!

The Cap'n

I found what appears to be the large flat washer - it was never installed.

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Sure looks like the right part to me.

I'm blown away that the fan stayed on the crankshaft for the last 3 years! I wish I could remember exactly how I installed the damn thing in the first place.

WOW! I can't believe it stayed in place for more than 5 minutes!

This made me go back and verify that my large washer was in place. It was but it never hurts to check.

It probably does not apply to this case but the team at my local race group say that the torque spec of ~23 ft/lbs specified by the factory is too low.

The fastest guy on the track says that he consistently uses the fan center bolt to turn his 10:1 CR motor over for timing adjustment all the time and has never broken a bolt (and never lost a fan) while the guys in the paddock right next to him HAVE lost a fan using the stock specs...

Stu