Transmission - Flwheel Information

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This section covers the flywheels fitted to the 3B and ABY engines, and briefly explains the advantages and disadvantages of the 'dual mass' flywheel that was introduced on the ABY engine. It was first fitted to the AAN engine of the UrS4, and is still fitted as standard equipment today on Audi's current models. The dual mass flywheel is not unique to the 01E gearbox either - for example it is used on the 1781cc I4 turbo engines with am 01A transmission.

The main purpose of any flywheel is give the engine momentum with a rotating mass, and to smooth out the delivery of power as each cylinder fires in turn. Like most things automotive, they are a design compromise between the desires of smooth running (implying a heavier flywheel) and free revving engine (implying a lighter flywheel).

Some engineering companies offer a service of lightening the flywheel as a performance upgrade - be advised this work should only be carried out by specialists with experience on the peculiar balancing requirements of Audi 5 cylinder engines. As a rotating component, the flywheel must be lightened and balanced along with the crankshaft, crank pulley and vibration damper - all bolted together on a special rig that can measure the imbalance in this rotating system. So don't expect such work to be cheap if you  are embarking on serious engine mods.

NOTE - When removing and refitting the flywheel, ALWAYS mark its position on the crankshaft with paint to preserve rotational balance and ALWAYS use new bolts.

Single Mass Flywheel - 3B (also RR and 10V I5 engines)

The flywheel fitted to the 3B engine is the same as the RR engine. It is a traditional single mass (SM) flywheel (as one large lump of machined steel) that bolts onto the end of the crankshaft. A total of eight bolts secure the flywheel to the crankshaft. These are very low profile bolts that require special care with sockets in order to remove and refit them.

This flywheel has 135 (one hundred and thirty five) teeth around its edge - these are counted by the engine speed sensor (G28) to determine the engine RPM info needed by the ECU.

In addition to the teeth, a number of crankshaft reference pins are fitted to the engine side of the flywheel. The main reference pin is fitted at 62 (sixty two) degrees BTDC on cylinder #1. A number of other pins are fitted to the flywheel at regular intervals. These are detected by the crankshaft position sensor (G4) for engine timing purposes.

A brand new flywheel does NOT have these pins fitted. As such, they must be purchased separately inserted into the flywheel. The correct height of these pins from the flywheel surface is 36mm (thirty six) ± 0.5mm.

Removal and refitting of the flywheel requires a suitable locking tool such as Audi's own 10-201 device. The correct torque setting for the single mass flywheel bolts is 30Nm (thirty) plus 90˚ (quarter turn).
Dual Mass Flywheel - ABY (also AAN and ADU)

Just about anyone who has driven a 3B and ABY engined S2 in a side by side test will comment on the 'smoother' nature of the ABY engine. This gives it a less 'raucous' character than the 3B engine. This is partly due to a more elegant ECU in the ABY, but more fundamentally because the ABY engine is fitted with a peculiar invention known as a 'two-part' flywheel - also known as 'dual mass' - or just 'DM' for short.

The pupose of the DM flywheel is to greatly reduce the torsional vibrations into the drive line where it would lead to resonant oscillation. What that does, in essence, is to make a considerable reduction of the speed range in which gearbox components absorb vibrations from the engine.

The main advantages of the DM flywheel are as follows :
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  • Better ride comfort
  • Absorbed vibrations
  • Noise reduction
  • Improved gearshifting
  • Longer life of gearbox internals
  • Reduced stress in drivetrain

However, the main disadvantage of the DM flywheel is that it makes the bottom end of the engine considerably heavier and less willing to accelerate as freely to high speeds as a traditional SM flywheel.

The DM flywheel, as it's name suggests is comprised of two parts. The first part, known as the primary mass is attached to the crankshaft and belongs to the engines mass moment of inertia. The second part, known as the secondary mass, also comprising the clutch, increases the mass moment of inertia of the gearbox.

The secondary mass rotates with the primary mass along a grooved ball bearing. Both masses are decoupled from each other via a complex spring & damper system. These springs allow torque to be transferred from the primary mass to the secondary mass. The dampers between the two flywheel masses are responsible for absorption of torsional vibration. This description is a gross over-simplification of the mechanical technology within the DM flywheel - it is a mechanical wonder and it works well. Take a look at this scarey cutaway view of the DM flywheel internals.

Removal and refitting of the flywheel requires a suitable locking tool such as Audi's own 10-201 device. The correct torque setting for the dual mass flywheel bolts is 40Nm (forty) plus 180˚ (half turn).
Flywheel Swapping FAQ

Q1. Can I put the single mass flywheel on in place of my dual mass flywheel ?

Yes - The 3B flywheel can be bolted directly onto the ABY, AAN and ADU engines with no concerns about number of teeth or the position of crank reference pins. They are identical in this regard.

Q2. What about clutch differences ?

A clutch suitable for the 3B engine can be used. It bolts directly on to the 'SM' flywheel as one would expect. This includes the many uprated clutches available from vendors like Sachs who offer some uprated road and motorsport spec clutches. Always check that the splines on the chosen clutch plate are compatible with the splines on the gearbox to  be used. Refer to the clutch section for more info.

Q3. What about gearbox fitment ?

With the ABY, AAN & ADU engines, a sizeable spacer is fitted between the engine and gearbox, in order to accomodate the extra width of the 'DM' flywheel. If the 'SM' flywheel is retro-fitted to the ABY engine, then this spacer can be removed so that the input shaft of the gearbox can engage with the splines of the clutch plate. With longitudional movement permitted in the engine mounts it is possible to locate the engine towards the rear so that it mount successfully with the original 01E gearbox. It is also possible to use the 016 gearbox in this configuration.

Last Updated 11th April 2004