QC54 Disaster: Bull Gear Teeth

I don't know that degreaser would do that although I'm not an expert. A strong caustic chemical is bound to have some effect although I've not been able to successfully reproduce any characteristic failure to date.

I wonder though about repeated stress failure? In the OP picture you can see at the extreme ends of the gear teeth as well as along the sharp corners of the teeth there is what looks like a delamination occurring. I've seen this before, most recently on a previously unused pulley (either NOS or reproduction, not sure) as well as on this example of a change gear.

In the case of the pulley, I was trying to true it up on the lathe and it just continued to fall away at the edges until it ultimately split in half. This gear though is really the dramatic example. The metal has disintigretated to the point it is expanded on the one side giving a substantial crown to the gear. It's quite amazing, really, I keep it around just to look at.

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It could be that some of these failures will become more common, I don't know. Age related due to the alloy, perhaps, and we will be seeing it crop up now for the first time since the parts were produced. Don't know, like I said, I'm not an expert. Just curious.

-frank
 
I think you are on to something there Frank. I always thought zmak was suposed to be the cure for zinc pest, but it could be quite likely it just gave the items more life, and not a vaccination. My first 618, had gears like the OP, I thought it was from a combination of weak metal, and **** poor operator. Luckily back in the 70's, a new set of gears was not that expensive from Atlas.

I learned the hard way not to use CLR on nickle plated tools.
 
The gear pictured in post #11, I would say that is certainly an example of zinc pest, but as far as I know it was rarely seen from Atlas, batches may have occasionally slipped through with impurities in the zinc. I've seen it also in small die-cast fasteners and metal toys. It's quite a disaster for collectors of the aforementioned toys since some of them command high prices- when they start falling apart...yikes
Fortunately Atlas gears are still in good supply on the used market.
Mark
 
Yes, as well as new gears. I've bought I think four within the past year. However, a new bull gear is probably a bit more expensive.
 
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