12V Dynamo + Alternator Black Billet Aluminium Top Pulley Bundle Kit

Upgrade your engine with this high-quality billet crankshaft pulley, designed to fit all upright fan shroud Type 1 aircooled engines from 1200cc through to 1600cc. Precision machined from solid billet material, this pulley offers superior strength, balance and durability compared to standard pressed steel pulleys.

The crankshaft pulley plays a critical role in driving the fan belt, which in turn powers the cooling fan and (depending on setup) the dynamo or alternator. A well-balanced pulley ensures smooth rotation of the crankshaft, reduces vibration, and maintains consistent belt alignment. This is especially important on performance engines where higher RPMs can expose weaknesses in standard components.

Unlike stock pulleys that can warp, crack or run out of true over time, this billet version is solid, heavy and engineered for accuracy. It spins exceptionally true, helping to reduce belt wear, prevent slipping and maintain optimal cooling efficiency. This makes it an excellent upgrade for both standard engines and an essential component for performance builds.

Important Fitting Information:
This pulley requires specific fitting hardware and shims to correctly set belt tension and alignment:
• 1 x Billet Pulley Nut (AC903112D)
• 7 x Billet Pulley Shims (AC903112S)

A complete bundle kit including pulley, nut and shims is also available under part number AC903112BKIT.

Fits:

Aircooled VW Type 1 Upright Engine Applications (1200cc–1600cc):
Beetle: 1960-1979 – 1200cc, 1300cc, 1500cc, 1600cc
Splitscreen Bus: 1960-1967 – 1200cc, 1300cc, 1500cc, 1600cc
Baywindow Bus: 1968-1979 – 1600cc (Type 1 engine models)
Karmann Ghia: 1960-1974 – 1200cc, 1300cc, 1500cc, 1600cc
Trekker (Type 181): 1968-1983 – 1500cc, 1600cc
VW Buggy / Baja: 1960-1979 – Type 1 based engines

This special chrome pulley nut and washer set is designed specifically for use with billet aluminium top pulleys, providing a secure fixing while delivering a high-quality custom finish to your engine bay. Manufactured to suit billet pulley designs, this kit ensures correct fitment and reliable clamping force where standard pulley hardware will not work.

Unlike factory pulleys, billet top pulleys (such as part numbers AC903112B and AC903112C) often require a different nut profile and seating surface. This chrome nut and matching washer are engineered to suit those pulleys, ensuring proper alignment and secure fastening to the generator or alternator shaft. The washer helps distribute load evenly across the pulley face, preventing damage and maintaining correct belt alignment.

The chrome finish not only provides corrosion resistance but also enhances the appearance of your engine, making it ideal for show cars, restorations, or detailed performance builds. It is a small but important component that ensures your pulley system remains secure under engine load and belt tension.

Installation is straightforward, but it is important to ensure the pulley, belt, and shims (where applicable) are correctly set up to maintain proper belt tension. Always check compatibility before installation, as this kit is not suitable for standard factory pulleys.

Supplied as a nut and washer set.

Vehicle Fitment

Aircooled VW (Billet Pulley Applications Only):

• Beetle (1960–1979) – All engines with billet top pulley
• Beetle Cabriolet (1960–1979)
• T2 Split Bus (1960–1967)
• T2 Bay Window (1968–1979)
• Karmann Ghia (1960–1974)
• Trekker (1968–1983)
• Buggy / Baja (Type 1 based, 1960–1979)

Fits billet top pulleys only (e.g. AC903112B, AC903112C). Not compatible with standard pulleys.

Key Features

• Chrome pulley nut with matching washer
• Designed specifically for billet top pulleys
• Ensures correct fitment and secure fastening
• Washer distributes load and protects pulley surface
• Improves engine bay appearance with chrome finish
• Not suitable for standard factory pulleys

Replacement pulley shims with a larger internal diameter, specifically designed for use with billet aluminium top pulleys that feature a larger square centre boss. These are not suitable for standard factory pulleys and are intended only for aftermarket billet pulley setups.

On aircooled VW engines, pulley shims are used to adjust fan belt tension by spacing the two halves of the crank or alternator/generator pulley. Adding or removing shims between the pulley halves changes how tightly the belt sits in the pulley groove. Correct belt tension is critical—too loose and the belt can slip, too tight and it can cause premature wear to bearings and components.

With billet pulleys, the centre boss is often larger than standard, meaning original shims will not fit correctly. These larger ID shims ensure proper fitment on the pulley shaft, maintaining accurate alignment and allowing precise belt tension adjustment.

Each pulley typically requires 7 shims in total, distributed between inside the pulley (for adjustment) and stored under the outer pulley nut (as per VW design). Having the correct number of shims ensures proper adjustment range and prevents damage to the pulley or belt.

Sold individually, allowing you to replace missing or incorrect shims as needed. Ideal for performance engines, custom builds, or vehicles running billet pulley systems.

For best results, ensure your pulley halves, belt, and retaining hardware are in good condition when setting belt tension.

Fitment

Aircooled VW

• Beetle Saloon & Cabriolet 1960–1979
• T1 Split Bus 1960–1967
• T2 Bay Window 1968–1979
• Karmann Ghia Coupe & Cabriolet 1960–1974
• Trekker (Type 181) 1968–1983
• Buggy / Baja (Type 1 based) 1960–1979

Product Details

• Application: Alternator/Generator pulley (billet only)
• Type: Large internal diameter shim
• Quantity required: 7 per pulley
• Sold as: Individual shim