BMW 3: Chain drive - Crankshaft drive

Features:

• Chain drive at the side of the engine emitting the forces.
• Single-part chain drive for driving the camshafts.
• Single sleeve-type chain 8 mm.
• Electric motor of the combined oil-vacuum pump via a separate chain.
• Plastic tensioning and guide rail.
• Hydraulic chain tensioner with spring preload and sealing sleeve.

The following comparison shows the differences between the timing chain drive of the B46 engine and that of the B46TU and B48TU engine:

Comparison chain drive B46 engine with B46TU

1. Two-part chain drive B46 engine
2. Single-part chain drive B46TU and B48TU engine

1. Slide rail
2. Top timing chain
3. Chain tensioner
4. Tensioning rail
5. Bottom timing chain
6. Camshaft sprocket, oil/vacuum pump
7. Drive chain oil/vacuum pump
8. Guide rail
9. Timing chain

The main difference between the chain drive compared with the B46 engine is the move from a two- part timing chain drive to a single-part timing chain drive. The timing chain direly drives the camshaft sprockets on the camshafts. Deflection via the intermediate shaft on the top timing chain and the second timing chain is no longer needed. The chains used here are 8 mm sleeve-type chains. Because the intermediate gearing is no longer needed, the number of teeth on the crankshaft (23 teeth) and the VANOS unit (46 teeth) has also changed.

Comparison chain track, B38 and B38TU engines shown

1. Chain track two-part timing chain drive (B38 engine shown, B46 is identical)
2. Chain track single-part timing chain drive (B38TU engine shown, B46TU and B48TU are identical)

1. B38 & B38TU engines shown
2. Upper timing chain
3. Timing chain
4. Lower timing chain
5. Drive chain oil/vacuum pump

The way the combined oil/vacuum pump is driven by a separate drive chain from the crankshaft has not changed. Only the renewal of the chain tracks has changed; the drive chain for the oil/vacuum pump is now located in front of the timing chain.

Eliminating the second timing chain offers the following benefits:

• Improved acoustics
• Lower space requirement
• Reduced weight

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