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Sun Feb 02, 2014 12:03 pm

Hi, 71 beetle, stock. I put a reman alternator on about 1,000 miles ago. After having the engine out for pushrod tube replacement and general cleaning,oil cooler replacement etc... got it back together and there is a loud knocking sound produced by the Alternator. I also put a new fan on it and doghouse.

When I take the belt off, no noise so it's certainly the Alternator. I've never heard an alternator make this kind of sound, usually they whine, scream, grinding noise, but not a knock. It really sounds like a rod knock, but the noise is absolutely coming from the Alternator. It happens at all RPM's Idle to cruising speed.

When I spin it by hand, no noise, no rubbing, grinding etc...of course I can't spin it very fast so I can't reproduce it.

Any thoughts or comments on the knocking noise? I'm going to pull the engine out to replace the oil pump & go with Oil pump and Filter all in one, so I want to tackle this at the same time. Just don't want to do something that won't fix it.

Thanks guys!

Sun Feb 02, 2014 12:15 pm

The oil filter and pump in one things can be installed with the engine in the car just pull off the front piece of tin and the pulley and there will be enough room to get it in there. Try pushing down on the alternator while you spin it I had my doghouse not seated correctly so when the fan belt was installed the alternator was pulled down a small amount and it rubbed.

Sun Feb 02, 2014 12:17 pm

The fan is probably rubbing the fan shroud. Loosen the bracket holding the alternator down and move it one way or the other

Sun Feb 02, 2014 12:53 pm

Took the nut and washer off, lots of metal dust, got the pulley off and I found the issue. I'll post pics In a bit. Outer pulley spun and wore a groove on inter pulley shaft. Easily making a knock knock noise as it slipped

Thanks for the advise guys, saved me an engine pull

Sun Feb 02, 2014 5:34 pm

Here are the pics, the outer pulley half wore a groove on the shaft of the inner pulley half. essentially the outer pulley half was slapping back and forth when it was running. I was able to hold it in my hand and move the outer half back and forth, exact same sound I was hearing.

Sun Feb 02, 2014 6:42 pm

yep, that's because its one of those shitty aftermarket empi or scat pulleys. the nicer spin true pulleys are the same, but made a lot better. original pulleys have two tabs one bigger and one smaller that fits into two corresponding holes around the shaft part. i have a stack of the crappy cheap ones that did the exact same thing. never had an issue with original, or spin true pulleys (last time i bought one, about 5 years ago, was about $40, versus $15 for the cheap ones)

Sun Feb 02, 2014 8:00 pm

you need to have enough shims in the pulley....usually around 10....otherwise the outer spacer will bottom out against the hub of the back half of the pulley,allowing the front half to rattle back and forth till it looks like yours...even though the belt feels like its adjusted properly....the crap pulleys usually have the rear half come off the hub cause they're not welded properly,but that's not what happened to yours

Sun Feb 02, 2014 8:21 pm

This is true, but even with enough shims, it'll still eventually do that with a cheap pulley. I took a trip to bugabuluza one year in my 72 super. Bout 100 miles away. I had just built a motor for it, and this was the maiden voyage, had a new empi pulley (came with a parts lot), and figured it would be ok, I get to the show just fine. As I'm pulling out, I hear that knocking. I see the outer pulley half is off center. I go back, find a scat booth selling the nice spin true pulleys, and it's been on there since, and that was about 5 years ago. Moral of the story: ya get what you pay for 8)

Sun Feb 02, 2014 8:43 pm

and never use the fancy tapered spacer and chrome acorn nut that comes with the chrome pullys....I've yet to see one of those that haven't come loose

Sun Feb 02, 2014 8:58 pm

I did not have it shim'd correctly :( I just ordered a German OEM replacement, I will shim it right this time.

Thanks guys, great help as always!!!

Sun Feb 02, 2014 9:18 pm

It's great that you caught it close to home. A buddy put a new pulley on- and 175 miles into a (noisy) trip on the freeway to WA- his pulley spun out. It lasted one trip- so was only stopped and started maybe 6 times.

Mon Feb 03, 2014 9:07 am

Hmm, I've never actually had a problem with the tapered washer and acorn nut. But mine is kinda old and doesn't screw on smooth, but kinda rough, so maybe that's why mine stays on, XD. But in my other motors, I just use the stock style nut and washer.