Drive Belt Check,
Adjustment and Replacement

Note: The only absolutely essential spare you need to carry in any
VW (besides the spare tire and the means to change it) is a spare
fan belt. If you try to drive your VW with a broken fan belt, you'll
wreck your engine within a few miles.

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This article covers the following topics -

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Checking the Drive Belt

Note: The belt should be at least tight enough so that turning the generator/alternator pulley with a wrench also turns the engine. If it is too loose, turning the pulley will just turn the generator/alternator shaft while the belt slips on the pulley. In this particular engine, proper fan belt tension is vital, since any belt slipping reduces the amount of cooling air that is supplied by the fan to the engine. Of course, having the belt too tight can cause premature wear on the alternator/generator bearings.

  1. The alternator/generator drivebelt, also referred to as a V-belt or simply fan belt, is located at the rear of the engine. Because this belt drives both the alternator and the engine cooling fan, the good condition and proper adjustment of the belt are critical to the operation of the engine. Because of their composition and the high stresses to which they are subjected, drivebelts stretch and deteriorate as they get older. They must therefore be periodically inspected.
  2. With the engine off, open the rear hood and locate the drivebelt at the rear of the engine. Check the belt for separation of the adhesive rubber on both sides of the core, core separation from the belt side, and/or severed core.
  3. Also check for fraying and glazing, which gives the belt a shiny appearance. Both sides of the belt should be inspected, which means you will have to twist the belt to check the underside Use your fingers to feel the belt where you can't see it. If any of the above conditions are evident, replace the belt.
  4. To check the belt tension, with your thumb push in on the belt midway between the pulleys and measure the deflection with a ruler. The drivebelt deflection should be about 5/8-inch. If the tension is more or less than this, it must be adjusted to bring the tension into specification.

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Adjusting the Drive Belt

Note: Adjustment for the fan belt tension on a Type 1 engine is kinda goofy compared to more modern cars. Since the generator/alternator is in a fixed place on this engine, VW had to provide for adjustment of the fan belt another way. They did this with shims. The alternator/generator pulley is really two separate halves. To adjust the belt tension, the pulley nut is removed and shims are added to or subtracted from the space between the pulley halves. Adding shims decreases belt tension, and subtracting shims increases belt tension.

  1. To adjust the belt tension, you must first remove the pulley nut. The front half of the alternator pulley (front is front) has some cut-out slots in it. Insert your big screw driver into one of these slots to hold the pulley stationary while using your 19mm wrench to loosen the pulley retaining nut.
  2. Note: VW supplied a tube spanner with every car just for this job (it also fits the wheel nuts and spark plugs!), but any 19mm box wrench (ring spanner) will do the job.

  3. Remove the pulley nut, and you see a metal bell-looking thing, and under that are some shims. Remove all that stuff and then remove the rear (rear is rear) pulley half.
  4. Belt tension is adjusted by inserting or removing shims between the pulley halves.
  5. Note: Although the shims are thin, removing or adding even one makes a considerable difference in belt tension.

    Note: Spare shims are placed just underneath the metal bell, so the complete stack of shims and pulley halves remains the same. This ensures that the nut will fit the shaft correctly, and the spare shims will be available for future use.

    Note: When removing the shim stack to replace the belt with a new one, it's a good idea to keep the the shims between the pulleys in a separate stack to the spares, so you have a starting point for the number of shims needed for the new belt. Most often, a new belt will require more shims between the pulley halves.

  6. Install the belt, shims as needed, the outer pulley half, spare shims, bell-shaped washer, and retaining nut. Make sure that the fat bell-shaped pressure washer is in place immediately under the retaining nut. This washer is essential in maintaining an even pressure around the pulley hub through the shim stack.
  7. Stop the pulley from turning with the large screwdriver as described above and tighten the nut securely.
  8. Note: You may find it useful with a stiff new belt to remove the locking screw driver and keep tightening the pulley nut so the engine turns over a few times. This will help the belt climb out of the valley between the pulley halves as they tighten. Replace the locking screw driver in the slot for the final tightening.

  9. Recheck the belt tension and repeat until the drivebelt tension is correct.
  10. Note: The problem with this adjustment method is that you have to guess how many shims you need to add or subtract, then put it all back together and check it. If it's still not correct, then you have to go back and do it again. This is not the best design, but it works.

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Replacing the Drive Belt

Note: The correct belt size for all upright Type 1 (Beetle/ Kharman Ghia/Thing/older Bus) engines (except 12-volt engines with alternators) is either 900mm or 905mm. The correct size for 12-volt engines with alternators is 11.3 x 912mm. The length is important because of the limited tension adjustment available in this engine design. Take the old belt to the parts store for comparison if you aren't sure.

  1. To replace a belt, follow the above procedures for the drivebelt adjustment, but slip the belt off the crankshaft pulley and remove it.
  2. Note: If you have piece of tinware around the back of the engine pulley you will need to remove it (three screws) to gain access to the engine pulley. Don't forget to replace this tinware afterwards - it helps prevent items falling into the valley around the engine pulley. Nothing cuts up a new belt faster than that missing screw!

  3. Remove the bell shaped spacer and the thin shims. Remove the outer half of the pulley, and the fan belt will come off. In-between the pulley halves, will be another group of pulley shims that adjust the belt tension depending on the number of shims used.
  4. Note: You must have at least 10 shims!

  5. Install all 10 shims between the pulley halves as a starting point, and place the belt into position while installing the other half of the pulley. Install the remainder of the shims (if any), then the bell shaped spacer, and tighten the nut down the same way you removed it.
  6. Make sure the key is off, then rotate the engine a full revolution and check the belt tension. You should be able to push the belt in between the two pulleys 5/8". No more, and no less. If you can move the belt more than 5/8", you will need to remove shims from in-between the pulley halves, and add more if you cannot move the belt 5/8".
  7. Note: The belt is tightened by moving the pulley halves close together, which makes the belt ride up higher, and this removes slack.

  8. Remember to rotate the engine between each fitting of shims, to make sure the belt is fully seated before you check it's tightness. Always put any extra shims between the pulley half and the bell shaped spacer for safe keeping for when you need to replace the belt in the future.
  9. Note: It is VERY important that you always make belt adjustments starting too loose, then slowly tighten up. This ensures that the pulley halves are tight against one another, though they may have shims between them (this is ok). If you make the mistake of trying to rush, and do not have enough shims between the pulleys, the belt will get tight before the pulley halves are seated (and the nut is tight), and when you run the engine the pulleys will wobble and destroy themselves, the belt, and maybe your generator or alternator. This is the most common mistake when adjusting the belt, so make sure you are patient and do it the right way to prevent walking at 3am on a rainy night. ;-)

    One last tip! How far out on the pulley your belt is also determines how fast the fan spins. Think about changing gears on a multi-speed bike. You can make a larger belt "work", but this slows the fan down and the engine will run hotter. Many cases of engine overheated are the result of the wrong size belt! Your engine will run cooler if you run the slightly shorter alternator belt, instead of the generator belt (they ARE different). This is one reason why the factory changed belts in mid 1973.

Adapted from product instructions received from Aircooled.Net, with our thanks.

 

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