New Pulley Question

Just received my new pulley with timing marks and am a little confused. I note on the back side that there a threaded section on the back (see pic.) Since the pulley pulls straight off after the nut is removed, what are the threads for?????. Also is there some kind of woodruff key that fits into the slot of the pulley that should be replaced. My repair manuals do not provide many details about replacing the pulley.
Troy

Don't worry about the threaded part, most aftermarket pulleys have that for reasons which are unknown to me. Just press it on, over the existing woodruff key on the crank. This should still be there from when you removed your old pulley

The spiral thread on the outside is a design factor to seal the crankshaft. If your engine block has been modified/machined for a sand seal that pulley design won't work. Off-roader's machined the engine casing end to accept a seal with a much smaller tolerance.

Thanks guys
Troy

pushes oil back in the case.

i think it's called a "labrinth" type seal

"Sand Seal" in most dune buggy ads.

what i meant was, the pulley has a labrinth seal. pressure/air would cause a little blow by at that point so the lips kindof slow the air/oil movement down and more stays inside the case.

Bruce what you are trying to say is ... It's a cork screw type thinga-ma-gig! YA spins the oil back into the crank-a case.

i knew you'd get it.

The reverse threads found on the backside of a pulley is a built-in oil slinger. If you've ever opened up an engine case, you'll see VW provided no actual seal at the pulley end of the crackshaft as they did for the flywheel end. When oil tries to escape the case, it travels into these grooves. Being a reverse thread design, it flings the oil back in. If oil does manage to escape and leak at this area, you may need to install a working breather system as there is too much pressure built up inside the engine.
A sand seal pulley is completely smoothed over as not to tear the seal. Sand seal pulleys are favored by the dune buggy crowd to prevent dirt entering the engine case since there is no actual seal provided at the factory.

And..as an interesting note, 356/912 engines did have a seal at this area as well.

Off to the store to get a 30mm socket