It's made to look as though it should have a real key holding the timing gear in place. But there is no key. The timing gear just has a tiny little nub that guides the gear into the proper alignment. Then another tiny little nub pokes out into the slot on the pulley to alignment. Once everything is aligned, the big bolt squeezes the pulley onto the crank, which is what really holds the timing gear in place, not the little nubs.

It's a mildly feeble system. One of the things that gives me some grey hairs on my 16V swap - where a slipped timing gear could result in some valve carnage.

There are a couple of companies that make tougher timing gears that use real woodruff keys. Might actually hang together for a little bit (until you get the motor shut off) if the pulley comes loose. But that's not really such a big deal on the 8V motors - they're non interference.
--
'63 PV544 rat rod, '93 Classic #1141 245 (now w/16V turbo)