Vintage VW Generator Pulley Discussion

Recently, a potential customer called, needing a Generator Pulley. His, he told me, had self-destroyed! “Do you have any?” he asked.

I replied that I did have a stack of Pulleys but that he should bring his Pulley so that we could match it.


Destroyed was an inadequate description of his Pulley and its parts. As we surveyed the parts, the customer explained what had happened. I never fully understood what had happened, but…

I think that it was incorrect placement of the Spacing Shims (washers) so that the Pulley Nut could not be properly tightened. Take a look at the damage:

The first thing which I noticed was that the Pulley was a chromed after-market version. Chromed surfaces are not just smooth—they are slick so that attempts to properly torque a bolt or, in this case, a nut, can be inexact.

Powder-coated surfaces pose the same problem. I made the mistake, once, of sponsoring the powder-coating of engine components, including the Generator Pulley. The resultant difficulties cured me of powder-coating Pulleys of any kind.

I’ve been chastened for saying that, but if I save one person from the problems of chrome and powder-coating—I’ll die happy!

What did I do for this customer? We sorted genuine German Pulleys until we found a really nice, used Pulley which was going to get the job done. Also, a Woodruff Key (shaft key), 8 good Shim Washers, a good German Pulley Coned Washer (or collar) and a Pulley Securing Nut.

I want to say something here about the Shim Washers. I have accumulated a box of Generator Pulley Shims over the years and draw from them when I need some. Over time, I noticed that some Shims are quite flimsy and are easily bent. They appear to have been stamped from thin sheet metal which has left raised edges. I prefer the less flexible Shims (see specifications at the end of this discussion).

Let’s look at a Genuine German Pulley which would have come on a 1967 Beetle Generator.

In the Owner’s Manual, the Glove Box Edition which came with each VW, Volkswagen has a good illustration, with instructions, for installing and adjusting the Generator Pulley Belt. This should be The Standard when installing a 1967 Beetle Generator Pulley Belt and related parts.

1967 Beetle Owner’s Glove Box Edition Manual—Page 29

The Belt for a Generator always should be a V-Belt with NO notches. Notched Belts are for the Alternators in mid-‘70s air-cooled VWs.

  1. Be certain that you have the correct Pulley and Belt to install onto your Generator. Having the wrong Belt will lead to frustration when Belt Tension will not adjust properly. Having the wrong Pulley can result in the failure of Pulley, Belt and Generator.

  2. Be certain that the Crankshaft and Generator Pulleys are properly aligned. If the Generator Pulley is not in line with the Crank Pulley, strain will be placed on the Belt and Generator that can lead to Belt and/or Pulley failure—or perhaps worse! The Belt could flip off and the loss of ability to cool could cause pretty rapid Engine Failure through overheating. This may seem to be an unlikely scenario—but, I have seen misalignment of Pulleys.

  3. The number of Spacer-Shims: There always should be 8. The Shims are to be placed between Pulley Halves to alter the Tension on the Belt–more Shims causes the Halves to be separated farther and the Belt to “fall” farther between the Halves as a result. Fewer Shims between the Pulley Halves means that the Belt will ride higher between the Halves (because the Halves will be closer together). So, you need to adjust and check, adjust and check, until the Proper Tension is reached. Proper Tension can be determined by depressing the Belt at mid-point, on the side towards the carburetor/fuel pump. If the Belt can be depressed about 5/8ths inches (a little more than a half inch), proper Tension has been achieved. You don’t need to put much pressure on the Belt in order to check this deflection. Just a firm thumb on the Belt, depressing the Belt at mid-point. Test yourself several times and you’ll get the idea.

Now, let’s suppose that it takes 5 Shims between the Pulley Halves to achieve proper Belt Tension. What becomes of the “extra” Shims? They should be placed on the Outside of the Outer Pulley Half, between the Outer Pulley Half and the Coned Washer, which will be secured with the Pulley Nut.

But are these “extra” Shims really “extras”? “Not at all!” says Barry Blythe, the local VW Mechanic. These “extra” Shims serve to take up slack between the Pulley Coned Washer and the Outer Pulley Half. Examine the Generator Shaft End and you will see that the Threads do not extend past the Generator Pulley Halves. There are Threads sufficient to accommodate those few “extra” Shims and the Pulley Coned Washer and Nut. The “extra” Shims fill the void that will be left between the Outer Pulley Half and the Pulley’s Coned Washer and Nut. Otherwise, there would be a little slack between the Nut and the Outer Pulley Half and Coned Washer so that when the Nut is tightened (to the extent of the Threads), the Outer Pulley Half would be allowed to wobble. This would not be a good scenario! In short, the wobble would turn into a nightmare for the Complete Pulley Assembly, ultimately resulting in Pulley and Belt Failure and likely would damage the Generator. So, be sure that you keep those “extra” Shims and put them where they belong–between the Outer Half of the Pulley and the Pulley Coned Washer!

  1. More on Tensioning the Belt: Okay, so you have the Belt positioned between the Pulley Halves and are tightening the Pulley Shaft Nut. Seems tight, so you let it go at that. Wait! You now need to turn the engine by hand (use a wrench). You are going to find that the Belt will “seat” between the Pulley Halves. You may have to repeat the Adjustment Procedure several times until you have the Correct Number of Shims between the Halves so that the Belt rides properly between the two Halves and the Deflection at mid-point is about 5/8ths inches. Each time, after tightening that Pulley Nut, turn the Engine manually to “seat” the Belt in order to check for proper Tension! This is very important.

Why spend so much time discussing this Pulley and Belt and associated parts? Because—the life of the Engine depends upon these simple elements.

And, a well Adjusted Belt will see that the Battery remains properly charged.

Treat these components with care and your Volkswagen will return the favor in long-life and lots of enjoyment!

David Brown, our Go-To Parts Consultant supplies the following VW Parts Information:

  • The Pulley Halves are sold as a set of Inner and Outer Halves with the Original VW Part Number of 131 903 109. The correct Pulleys for 1967 are the ones with two “tabs” on the Outer Half and two “slots” on the Inner and with a round Center Hub.
  • The “Cone Washer”…..VW calls it “Special Washer”, is VW Part Number 111 903 183
  • The Shims (0.5mm thickness) are 111 903 131 A. VW calls them “Distance Washers” and the number required is noted as “x” which means “as needed”.
  • The Pulley Nut is 111 903 181
  • The Woodruff Key is N 012 705 1. These “N” Part Numbers are standard DIN parts and are 3mm x 5mm in size. The other Key on the Fan end of the Generator Shaft is the same.

These all are Original VW Part Numbers. The Pulleys, themselves, have been superseded a few times but the rest of the parts have kept their Original Numbers.

By the way, the Belt always has been 111 903 137 A for both 6v and 12v from 1955 up to when the Alternator replaced the Generator in mid-1973. How many other car makes have used the same Fan Belt for 20 years? (Note—the same Belt now is being sold as 111 903 137D)

Posted by Jay Salser

My wife, Neva, and I have been driving and working on VWs since 1976. In fact, we raised our family in these cars. Now, we are retired and enjoy VWs as a hobby. The ’67 Beetle always has been our favorite year. We own a '67 Beetle and a '68 Karmann Ghia.

  1. Really informative, JK!

  2. There’s an ancient passage in the Bible which says, in effect–“It’s the little Foxes that spoil the grape vines”! Meaning that it’s those little things, often overlooked, which cause greater problems when not responsibly managed.
    Thanks for editing and posting this discussion, Eric!

  3. From Karen Olansen.

    “You noted in your discussion about problems with powder coated pulleys. In my reading, I have seen stories about loose lug bolts after powder coating the rims. It was suggested that the powder coating be removed from the surface where the lug touches the rim. “

  4. Back to the basic ! Excellent article Jay and great engine picture ✌️

    1. Your engine! :)

    2. Hello, Guy. I keep thinking of you and hoping that you folks are doing well. Sort of an early COLD Christmas present this year!!! I pulled the ’67 engine photo from the internet. You may know–but, what is the tube leading from the driver’s pre-heat tube, around the engine and to ? It must be directing heated air to some component. Do you know? Otherwise–the engine looks mighty good and factory. Thank you for reading and staying in touch, Guy! jay

      1. Good question, I was wondering the same thing as I had not seen the rubber tube like that on any 67 Bug. May be a European fitting of some kind?

        1. Jerry…David Brown and I have talked about this. We believe that the T-ed Tube off the pre-heat paper tube may have to do with a gas-fired heater. David tells me that there are many “configurations”. Since his VW career has been in Pennsylvania, he has seen lots of cars from Canada–which were more apt to have the gas-fired heaters. So–that’s our theory–until we hear from Guy. Thanks for commenting! jay

      2. Hello Jay, I have sent you an email with the information on the heater booster for 67 Deluxe Beetle. Thank You Jay !

    3. Ha! The joke is on me! Eric swapped photos on me–that IS YOUR Black ’67 Beetle. Guy! jay

  5. Thank you so much for commenting, Karen. Please see this Link: Yes…some years ago, I became aware of the complications when critical elements of vehicles/machinery are powder-coated.
    Pulleys are very critical to the operation of the Volkswagen (Crank and Generator Pulleys). The mounting orifice MUST be left uncoated if a pulley is to be coated. Also, the surface where the V-Belt will run must remain uncoated.
    As a result, I find it easier to paint the VW Pulleys. They are easily painted and the paint can be renewed, at will.
    Professional applicators know the procedures for protecting critical surfaces and orifices. But–in my experience, not all of them take the time to protect those critical areas. It’s up to the owner of the parts to be diligent. I continue to run across bad experiences regarding powder-coating. That said–powder-coating offers fine and durable surfaces which will last for extended lengths of time and continue to look good. jay

  6. This should be a test for reading skills, Jay. It would not be your fault if anyone misunderstands any of this.
    This tensioning setup is one of those things that amaze people who are not familiar with VWs. Makes for lively conversation.
    The process certainly needs to be done by someone who cares about what they are doing.
    If they are still selling the Idiot’s Manual, your contact info should be included for any clarification.
    You are an integral part of my ’67 ownership. Thanks.

  7. Hello, Fritz…coming from you, a very well published author–I humbly accept your comments. It causes me to want to do better. Keep enjoying your ’67 there on the Farm! I guess that I never have asked, but…does Dawn also enjoy the Beetle? jay

  8. Folks–David Brown tells me, in a separate off-line comment, the following story–and I quote: “Here’s a good short story……While I was working at Volkswagen a woman came to the service department and said her Fan Belt broke. The Service Manager was alarmed since she drove it in. She said ‘I took off my pantyhose and tied it round and round the pulleys.’ It worked, I saw it !! Of course, no one had a camera in their pocket in those days, HaHa.” (David Brown).

  9. I have been prompted by two comments outside of this WebSite. The comments had to do with “Hydrogen Embrittlement”. I mentioned the slick chrome as possibly permitting faulty torquing of parts. Hydrogen Embrittlement is more insidious. Read from this commentary regarding parachute equipment:

    From p. 96, The Parachute Manual by Dan Poynter (2d edition, Parachute Publications, Santa Barbara, 1977):

    “4.104 The Plating of Hardware

    FAA Advisory circular 105-2: 5, b (8) reads; “PLATING OF FITTINGS. Plating or re-plating of load-carrying parachute fittings may cause hydrogen embrittlement and subsequent failure under stress unless the plating is done properly. Chrome or cadmium plated harness adjustment hardware may also have a smoother finish than the original and may permit slippage. The parachutist should be aware of these possible hazards.”

    All plating is not the same. The result may appear similar but the strength of the finished product depends on the plating process used.

    Most hardware is plated with cadmium to Federal Specification QQ-P-416, Type 1, Class 1,2, or 3. This is a fairly simple process whereby the piece is run through the plating bath and then “Baked.” When re-plating with cadmium, the old plating must be removed and this must be done in a cyanide bath (rather than acid). Decorative plating, on the other hand is very attractive but difficult and tedious to do. The old plating must be stripped off. The metal must be buffed, copper plated, buffed again, nickel plated, buffed again, and chrome plated followed with a final buffing. All of this handiwork is very expensive and to further complicate the process, the hardware must be baked after each plating.

    The plating bath is usually an acid solution and all acids contain hydrogen. The hydrogen enters the pores of the metal and rearranges the molecular structure rendering it brittle. hydrogen embrittlement is most apparent in spring parts because of their small cross section. Their resiliency is damaged by the hydrogen, not by any heat treating to which they have been subjected.

    Magna-fluxing (magnetic particle inspection) will not pick up hydrogen embrittlement and the plating will fill up any cracks which may have developed. The hydrogen does its damage and leaves so there is nothing to detect until the piece fails in use. Quality doesn’t help either: the harder the steel, the more susceptible it is to hydrogen embrittlement.

    BAKING. However, all is not lost. If the plated hardware is placed in an oven at 375 Fahrenheit degrees for a minimum of three hours WITHIN FIVE HOURS AFTER THE PLATING PROCESS, the hydrogen may be “Baked” out and the original strength of the metal may be retained. But take note: once this five hour period has passed, the damage is done. After this, no amount of baking will restore the hardware to a high percentage of its original strength.

    Plating shops should be picked carefully. The “Junk chromers” who specialize in bumpers and other ornamental work are not concerned with strength and most do not have an oven; many are not even aware of hydrogen’s damaging effects.

    Parachute hardware may be properly chromed but it is so difficult and expensive that it rarely is. Because of the problems involved, cadmium plating is recommended. Good cadmium plating facilities with ovens may often be found on some large airports; use one which specializes in exacting aircraft work.”

    My take-away from this information is that crucial parts should not be chrome-plated. This includes the two critical pulleys for the air-cooled Volkswagen. jay

  10. Danke aus Deutschland, Salser.

    1. danke fürs lesen und kommentieren, Hubler! Many thanks for reading and commenting on this article, Hubler! jay

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