Front End Auxiliary Drive Systems
Enhance your auxiliary belt’s life with a kit of parts.
The humble fanbelt has come a long way. Fitted originally to run the fan that cools the engine and drive the alternator, it is used now to transmit power from the crankshaft pulley to an increasing number of ancillary components. For this, the belt has had to evolve: improved design has seen multi-ribbed auxiliary belts (sometimes called serpentine belts) and pulleys become universal.
Materials have changed, too. Most conventional vehicles from the last 10-15 years use belts made from ethylene propylene diene monomer (EPDM). This is relevant, because a DIYER must consider that the traditional method of identifying wear at service time, such as checking the running surfaces for cracks, or perishing, is not as relevant as it once was.
Additional components have been added to reduce vibration, plus enhance belt life and efficiency, such as tensioners and idler pulleys. The alternator pulley may be either an overrunning alternator pulley (OAP) or an overrunning alternator decoupler (OAD), both of which are designed to protect the belt drive components from premature wear. While there are different ways of detecting pulley wear, which differs between OAP and OADS, should you notice that the tensioner oscillates excessively when the engine is running, then the alternator OAP/OAD will need replacing as well. Unless official maintenance intervals state otherwise, check the FEAD system at 60,000 miles and change all components at 90,000 miles, regardless of their condition.
The auxiliary belt should not be thought of as a single component, but as one part of a front end auxiliary drive (FEAD) system. Rather than change the belt on its own, you should replace all of the components that make up the FEAD system at the same time, as you would when replacing a timing belt. Quality suppliers have developed kits of FEAD parts for particular makes and models. This feature details the fitting of a kit of Oe-quality components, using specialist Laser tools from Tool Connection.
All work must be performed in a clean environment and the vehicle’s battery on conventional engines must be disconnected. Hybrid systems must be isolated, so that there is no risk of the engine starting while you are working on the pulleys. Do not wear loose clothing, and long hair should be tied back.
1 The FEAD system on this 2006 Citroën C5 2.0 HDI diesel had covered 108,000 miles. Many technicians recommend that the change interval coincides with that of the timing belt. Check your car’s manual for recommended replacement intervals, or follow our earlier replacement advice.
2 FEAD systems can, sometimes, be difficult to access, due to being positioned very close to the inner wing. Laser Tools sells a slimline toolkit (part number 3757) for £60.65 to make the task considerably easier (see Step 5).
3 On this car, turning the pulley bolt (shown in Steps 4 and 21) clockwise raises the spring-loaded tensioner, which relieves the pressure on the belt so that it can be unhooked. Make a note of how it is routed round the pulleys.
4 For clarity, we have removed the plastic pulley from the tensioner. This particular one has a lefthand thread; turning the bolt clockwise unscrews it. It would be ordinarily unnecessary to remove it unless access is especially difficult.
5 We removed our pulley to improve access to the tensioner retaining bolt (see inset pic as removed). This one has an 8mm Allen key head – the Laser slimline tool proved invaluable here to gain sufficient leverage.
6 Should a lack of access mean you have to take off the alternator, remove parts that might obstruct the work area. In this case, the diesel fuel filter moulding had to be disconnected, taking care not to drip fuel over the alternator, which could damage it.
7 Remove protective cover(s) and disconnect all wiring from the alternator. Manipulate any wiring clips from the alternator body and tuck the wiring safely out of the working area, where it cannot be damaged.
8 Undo the alternator fixing bolts. Thanks to the automatic spring-mounted belt tensioner, even tension is applied continually, should the belt stretch. This was not the case on older cars, where the alternator was bolted solidly to a bracket.
9 Extract carefully the alternator from the engine bay and check it visually for a cracked casing, or any evidence of damage. If a new/ remanufactured alternator is to be fitted, ensure that a fixed pulley has not been used to save costs.
10 While OAP and OAD alternator pulleys differ mechanically, the replacement procedure is the same. OAPS (and some but not all OADS) are protected by a plastic cap. A fixed pulley (pictured left) will not have one fitted.
11 The plastic pulley cover (if fitted) can be prised away and discarded. A new one should be supplied with your replacement part. Should oil be seen leaking out, it is a sign that the pulley needs replacing.
12 Should an INA pulley be fitted, identify it by the ‘F’ number printed behind the cover (circled). Several replacement kits may be specified, depending on the car’s alternator manufacturer; the original ‘F’ number on your alternator provides a definitive answer.
13 Special tools are required to replace alternator pulleys. Laser Tools provides Diy-orientated answers to the professional tools. This is part number 6750 and costs £27.74 including VAT.
14 On this Mitsubishimanufactured alternator, the splined section of the special tool engages with the pulley, through which a Hex bolt extension passes to slot into the alternator shaft. Never use an impact wrench, only hand tools.
15 The Hex bolt is used to hold the alternator shaft while the pulley is rotated anticlockwise. Once loosened, the tools can be dismounted and the alternator pulley unscrewed from the shaft by hand, prior to being discarded.
16 Check that the alternator shaft is in good order, prior to confirming that the replacement pulley is fitted the correct way round. Screw the new pulley along the threads by hand until it locks into place.
17 Again, using hand tools only, fit the special tools as described in Step 14. As with Step 15, a ring spanner is preferable to the open-ended spanner, pictured. Final tightening should be performed with a torque wrench – the specification should be provided with your kit. For ours, the figure is 85Nm.
18 Finally, fit the plastic protective cover. Do not be tempted to reuse the old one – the lifespan of the alternator pulley will be reduced, or damaged considerably should you elect not to fit a new plastic cover.
19 Fit a replacement belt of the same specification. Never fit a cheaper and incompatible belt, if the original part had specific technical requirements (see page 38). This one matches the old one’s specifications: 6 ribs of 1217mm length.
20 A worn belt, made from EPDM, is not identified by perishing. The old belt (left) has had its grooves cut deeper by the metal pulleys and the ribs have worn, which has narrowed their shape. Some belt suppliers offer a gauge for assessment of wear.
21 Pictured are the old (left) and new automatic tensioners. The pulley centre bolts that are used to manipulate the tensioner to remove pressure on the belt are pictured more clearly. The bolt on the new part must not be unscrewed.
22 The new tensioner is offered up to the engine block, with any locating pins that form part of the casting being fitted to the appropriate recess. The fixing Allen key bolt on this tensioner is then fitted and tightened.
23 The centre pulley bolt (shown in Step 21) is manipulated to position this tensioner, enabling a locking pin (a 4mm diameter drillbit will suffice if one is not available) to be inserted into the recesses.
24 The alternator is then refitted, mounted to a fixed point (unlike many older cars, where alternator positioning dictated belt tension). Obviously, this negates the old practice of levering against the alternator after the belt has been installed.
25 With the alternator in place, the locked tensioner allows the new belt to be positioned loosely around the metal multi-ribbed crankshaft, alternator, airconditioning and the plastic tensioner pulleys.
26 Step 23 is repeated, this time with the locking pin removed. The torque on the tensioner pulley bolt is relieved gradually, as the tensioner applies pressure to the new belt. Check that the belt is aligned correctly on the pulleys.
27 Refit any removed parts, such as the alternator’s connections and the battery. Start and stop the engine, then check that the belt is still routed correctly. Press on the belt to confirm the tensioner moves freely and that its end stops are not touching.