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Alternator pully failure

Posted: Sun Oct 15, 2017 9:52 am
by mlrailguy
I was noticing a lot of unusual noise while playing in the dunes last weekend. This is what I found. Have been running this for 18 yrs. Also the key is sloppy enough to fall out of keyway. Was able to wiggle back half off with two screwdrivers.

Re: Alternator pully failure

Posted: Tue Oct 17, 2017 7:21 pm
by mlrailguy
OK, I only had 4 shims on here, so guessing it was never actually tight. This allowed the pulley to rock on the shaft , I assume. The key is actually worn enough that it just drops into keyway. Is this normal? Shouldn't it have to be tapped into the groove? Am I going to need to buy new alternator?

Re: Alternator pully failure

Posted: Wed Oct 18, 2017 8:52 pm
by Marc
Thou must always have a total number of shims (between the pulley halves + stored under the cup washer) no less than eight. Any less and the nut may run out of threads before the halves are cinched together.
VW abandoned the tab & slot setup in favor of the "043" style pulley which has a D-shaped snout on the front half with a matching opening on the rear half. I prefer the late style but the early setup works OK provided there are enough total shims in place.

Ideally the Woodruff key should fit snugly in the keyway - if it starts out sloppy it can only get worse over time. I was stranded in a small town in Wyoming coming back from Sturgis in 2016 with a bad alternator; took a few days to get a NAPA rebuilt shipped into town and when it arrived the keyway was loose. Didn't want to wait another three days for another with no promise that it would be any better so I went with it. It did make it home 1000mi to Seattle but just barely, destroying the pulley as well in the process.
Pulley - 1000 mi on First NAPA Alternator (Copy).JPG
First NAPA alternator (Copy).JPG


Got another one on warranty at the local NAPA store and it had the same issue, just not quite as bad. By this time I was disgusted with NAPA's core-inspection standards and decided to just run it until it dropped. I used a punch to deform the surrounding material enough to close up the slot. When I found a good deal on a new alternator I put that in the trike and retired the "fixed" one to a car that never leaves town ;)

Clamp the key in place with Visegrips and have a helper support the shaft from below with a massive object (to prevent damage to the bearing) while you peen the shaft to close up the slot...then flip over to the other side and repeat. Use a small file or sandpaper to knock down the surrounding disrupted metal if necessary to allow the pulley half to slide past.
Second NAPA Alternator 2.JPG

Re: Alternator pully failure

Posted: Mon Nov 20, 2017 6:25 am
by petew
I just took the key out and tightened it up. Fixed. Modern alternators don't have keyways. But yeah, that pulley is nasty. :(