Mysterious BHW Camshaft Hub Keyway Damage

After months of struggling to diagnose a timing problem on my 2005 Passat wagon I discovered that the keyway on the camshaft sprocket hub had been damaged somehow, causing the timing to be extremely advanced. The mystery is that prior to pulling the engine (to do a BSM delete and a manual swap) the engine had been running perfectly. I brought the engine to a mechanic (who turned out to be an incompetent con) to do the BSM delete. In the process he also installed a new timing belt and water pump. When I reinstalled the motor in the car it would barely run and because I removed and reinstalled the engine twice (another story) and had the ECU tuned I assumed the problem was human error. I checked the timing belt about 5 times before I pulled the camshaft hub off and discovered the damaged keyway.

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The first picture shows the normal key, the second shows my damaged hub. The key is one with the hub, not separate, and it appears like the key has been sheared to be offset. As far as I know the engine has not had any catastrophic events.
After installing a new camshaft hub the car ran perfectly.

My questions are-
Has anybody seen this kind of damage before?
How does this happen?

I guess that makes sense. It’s hard for me to imagine that someone with enough experience and the special tools to remove the cam hub could be so careless. I bought the car from the original owner at 140,000 miles. They said they only got it repaired at the vw dealer. After I discovered it I went back to the dealer and looked through all the repair orders and don’t remember any cam or cam seal work.
So either the guy who did my BSM delete messed with it for some reason or a previous mechanic who somehow compensated the timing to make it run right despite the hub being off. As I said, before I pulled the engine the car ran well.
Thanks for clearing that up.

I’ve had one like that. It also had a misinstalled air filter and some dumb after market fuel filter that was configured in such a way that absolutely no filtration was occurring. There are some real boobs out there.

Anyway you’ll need to get a sprocket from either BHW or BEW. BRM won’t work. FYI.