Polo cam pulley - Worn woodruff key - Roberson

In the above link is a photo of the camshaft pulley off my Polo. The photo was taken during the head gasket replacement whilst up in Scotland. Hopefully you can make out the rather 'chewed' woodruff key, which was so badly worn; it was possible to put the timing out by two teeth. Also, you might be able to see that the face which would be against the end of the cam shaft is blue. With no choice, the part was re-fitted so we could get home. But when the car was in for tappet replacement not long after, the garage replaced it, as a precaution.

The question is what could have caused it?
Polo cam pully - Worn woodruff key - none
The key is used for locating the gear in the correct position on the camshaft, once everything's tightened up, it's redundant. It does provide a backup if things aren't tightened correctly, but this is what happens.
Polo cam pully - Worn woodruff key - Civic8
Possibly a mixture of incorrect key fitted and incorrectly tightened bolt,that would be my guess!.

Polo cam pully - Worn woodruff key - Roberson

By look of it, it?s been 'slack' for a while. With the valve timing out by that much, I?m surprised damage wasn't experienced elsewhere.
Polo cam pully - Worn woodruff key - Peter D
The bolt has a blue treadlock coating on it and it may have lock priot to being torqued up may be even when it was firsat built. I assume you have replaced the damaged parts and replaced the bolt with a new one. Regards Peter
Polo cam pully - Worn woodruff key - Roberson
As far as I can recall, the bolt was fine, and didn't show any sighs of thread lock coatings like locktight etc. My uncle (an engineer) and the garage were both happy the bolt was ok to use again. But yes, the pulley was changed.

I have a feeling it was done by the garage the previous owners used. It had the HG replaced a long time ago during their ownership, so the chances are when the head was off the first time, this was when the damage was done. They didn't even change the oil after the HG failed, hence it was back in a thousand miles later for a bottom end rebuild.

First I knew about it was when the bolt was slackened, the pulley had a considerable amount of free play before the bolt was fully removed. When the pulley was removed from the end of the camshaft, this was what we saw.

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