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Timing Belt Replacement
By Doug Banning

The following procedure is to be used on the A8 4.2 32 Valve (ABZ) motor. This engine was found on the 1997 to 1999 U.S. bound A8's. This procedure can also be used for the 3.7 V8 engines. Much of this procedure is applicable to the 2000 and newer 4.2 40 valve (XXX) motor. However, the cam locking devices are different. Please consult the Bently manual when using this procedure.

Click here for a PDF version of this procedure, easiest to print out and use a checklist when performing this job (2.3 Mb). You can right click on it and choose "save target as" and download it to your computer.

Standard Tools Required
Special Tools Required
You can rent these tools from, click here to find out more.

When a position is referred to “Right Side”, this means the passenger side of the vehicle. “Left side” is therefore the driver's side of the vehicle (Left-hand drive models).

General Note
Whenever a part is removed from the engine, all corresponding attachment hardware should be kept with it for easy reinstallation. Clean all parts before installing back onto the engine.

Remove the Front End
The following procedure does not show the front end removed. It was done with the front end installed. This procedure is much easier if the front end is removed. It will save a significant amount of time and a few knuckles. Follow this procedure for front end removal first, then pick up this procedure and continue forward.

Removing the front end for this procedure can save a significant amount of time and a few knuckles. Follow this link for the procedure.

Replace the Oil Cooler O-Rings and Plastic Pipe
Sooner or later the oil cooler o-rings and plastic connecting pipe will harden and go bad resulting in an oil leak or coolant leak at the right front of the block. With the front end removed and the right side timing belt cover off, it takes about 1 to 1.5 hours to change the oil cooler o-rings and plastic pipe. Parts are about $30. Remove the front end, the right side timing belt cover, and follow this procedure. It is significantly easier with the front end removed. You won't need all of the tools laid out in the procedure, just a few of them.

Remove Covers
Remove the air intake breather tubes (2) from the front of the engine compartment to the air box. The cover at the front of the engine is clipped in place- simply lift it straight up and it will come free.

Remove the air duct that runs from the air box to the throttle body. Loosen the two hose clamps (one on each end) and carefully loosen the rubber from the attach points.

Remove the three plastic engine beauty covers. Start with the two outer pieces (held in place with two allen head bolts each). Then remove the center cover (held in place by four allen head bolts).

After removal of the covers, you should see this
(replace the oil filler cap so junk doesn't fall in!)

Drain Radiator
Remove the noise insulation panel under the engine (large plastic cover). Place a bucket under the car that can hold 3 gallons. Connect a short length of tubing to the radiator drain (labeled "K" in the picture below). Remove the oval-shaped bumper cover from the driver's side front bumper (pry out with small flat-blade screwdriver- the slot for the screwdriver is towards the center of the car). Remove the overflow reservoir cap.

Open the two high-point bleed ports at the driver's side rear of the engine compartment. Disconnect the auxiliary water circulation pump electrical connector.

Open the blue stopcock several turns and drain the radiator. If you are changing the radiator fluid at the same time, then remove the two lower (engine mounted) drain plugs. Use low pressure air to blow out the radiator through the overflow canister's fill port.

Remove Radiator Hoses
Once the radiator has been drained, remove the two water hoses from the front of the engine. Remove the plastic bracket attached to the passenger side timing belt cover that holds the two hoses in place.

On the upper hose, loosen the hose clamps and CAREFULLY break the hose free from its mounting points. The upper hose is connected to the engine in two places and the radiator in one place. Completely remove this hose.

After the removal of the upper hose, a second hose becomes visible. Loosen the hose clamp on this hose where it attaches to the engine and carefully remove from the engine. Simply swing this hose out of the way to the passenger side of the engine- no need to disconnect at the other end.

Remove the Two Cooling Fans
Remove the two bolts holding the passenger side fan shroud onto the radiator.

Using a 10mm wrench on one of the three fan pulley bolts to hold the fan still, loosen the large nut holding the fan onto the pulley (big Crescent works great). NOTE- THIS IS LEFT-HAND THREADED- DO NOT TURN TO THE LEFT TO LOOSEN! DAMAGE MAY RESULT!

Once completely loosened, remove the fan and shroud as an assembly by lifting straight up. (The lower portion of the shroud is held in place by clips that are disengaged by lifting the shroud straight up.)

The electric fan removal is a little trickier. First, remove the body pin holding the fan in place- it is located on the fan shroud towards the center of the engine and lower (it would appear at 8:00 if you look at the fan from the front of the car). Use a long flat-blade screwdriver to break the pin- there is no way to remove without breaking it. See photo.

Once the pin has been removed, the electric fan and shroud can be removed as a single unit by carefully lifting up on the small tab located at the 3:00 position (viewed from front of car) on the fan shroud and rotating the entire assembly clockwise (viewed from front of car- the top of the fan shroud moves towards the driver's side of the car) approximately 5 degrees. Then the assembly can be pulled out of the radiator shroud towards the back of the engine. Several zip-tie electrical cable tie downs must be removed in order to set the fan assembly off to the driver's side of the engine compartment. These are reusable, and can be loosened by pressing down on a small tab while pushing on the end of the tie.

Remove Serpentine Belt, Fan Pulley and Timing Belt Cover
Using a permanent marker, mark the serpentine belt's direction of rotation (I use clockwise for consistency) so that it can be reinstalled in the same orientation. If replacing the belt, this is not necessary. Remove the serpentine belt by pulling up on the tensioner stud (counter clockwise rotation viewed from the front of the engine) using a 13mm deep socket and 3/8” drive, with the drive handle towards the center of the engine. By pulling up on the tensioner, it should loosen the belt, and you should be able to easily remove the belt from the myriad pullies it involves. In the photo below, the serpentine belt has been removed in order to see the tensioner bolt.

Remove the fan pulley from the front of the passenger side timing belt cover by removing the three bolts holding it to the bearing assembly.

Remove the driver's side timing belt cover by removing the two large hex-head shoulder nuts from the face of the cover. You may need to gently tap the cover with a rubber mallet to loosen it for removal.

Using special tools 3197 and 2079, loosen (do NOT remove yet) the large bolt at the center of the harmonic balancer. The engine must be rotated such that the holding tool engages the harmonic balancer AND fits in the grooves in the passenger side timing belt cover casting (see the photo below). Use a ½” drive breaker bar with the special tool to loosen this VERY tight bolt. Loosen approximately 1 turn until it loosens.

Remove the left and right rear cam covers- located at the rear of each cylinder head.

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