A4 Tdi- changing Auxiliary Ribbed Belt, 1Z engine
Site user, Donald Teare, provides this article which covers the changing of the ribbed ancillary belt tensioner and the viscous fan coupling bearing, on his sisters 95’ A4 Tdi with a 1Z engine.
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Most modern cars now use one so called ‘ribbed belt’, to drive the ancillaries on the engine e.g.: water pump, alternator, power steering pump and fan (if not fitted with electric fan). The ribbed belt on this car uses a tensioner that consists of two alloy half’s which are held together by a long bolt through the middle, that allows movement between the two. Fitted in between the two half’s is a large spring that locates in each half, and provides the tension.
(Click images for larger version)
Photo: 1.The bolt that keeps the two half’s together protrudes out from the rear of the tensioner and this is used to mount the tensioner on the engine ‘bracket’, via a nut.
If you look at photo: 2, this is shown along with a protrusion that not only locates the rear of the spring but acts as a location peg in the mounting bracket, and stops the rear of the tensioner turning. The front of the tensioner is free to move in a clockwise and anticlockwise direction.
photo: 3, a jockey pulley wheel is bolted to the front half of the tensioner and hence tensions the belt. The spring tension is in a clockwise direction, and to release the tension on the belt a spanner is used on the mounting bolt for the jockey pulley wheel in an anticlockwise direction. The jockey pulley mounting bolt has a ‘left hand thread’, hence it will not undo when you turn it to the left, in effect you are not turning this bolt but rotating the front half of the tensioner against the spring.
Ok, that is the science bit, now for the reasons it required changing.
A little while ago, I noticed that the belt tensioner jockey wheel was not vertical to the front of the engine, and seemed to be moving towards the front of the car. Over time this became worse and when my sister complained of a noise when the car was started, I suggested that the tensioner was not right and needed changing. A new tensioner was purchased and my sister decided to leave changing it until the routine service was done. This changed one weekend with the car making a terrible racket. On lifting the bonnet you could see that the belt tensioner was much less than vertical and was putting a strain on the belt. The alloy front part of the tensioner was now so far forward that the viscous fan pulley was now grinding its way into the metal and causing much of the noise from the engine.
Photo: 4, arrow 1. It was decided to take the car round to my father’s workshop that Saturday afternoon to replace the tensioner; thinking it should be done that afternoon. How wrong we were!
The instant the tension was released on the belt our next problem was found. The bearing for the viscous fan pulley had collapsed resulting in lots of movement and noise. V.O.R. as they say in the trade- (vehicle off road) as there was no chance of getting a bearing until after the weekend. The lock carrier (this is the name given to the front panel of the car that the radiator, headlights ect, mount to) was moved to the service position, which gives better access to the front of the engine. Removal of the viscous fan (coupling) was next as this has to be removed before the belt tensioner can be replaced and to change the bearing for the fan coupling. You have to counter hold the viscous fan pulley while removing a 8mm allen key bolt that holds the pulley to the bracket (the bolt goes through the middle of the bearing). Can be tricky if you don’t have the right tool for the viscous fan. Then the belt tensioner is removed by unscrewing its mounting nut.
Photo: 5, shows the belt tensioner and hopefully you will be able to see that the top of the front half is forward at an angle, top section longer than the bottom. Photo: 4, arrow 2, you should be able to see that the ‘flanged washer head’, of the bolt that passes through the tensioner has worn away at the top. There is a lot of brown rust to be seen and also in photo: 6, the dust from the rust on the back of the jockey pulley. It is also possible that behind the flanged head bolt and reaction plate, the alloy casting of the tensioner has worn, but as of writing this
I have not stripped the tensioner down to check.
With the engine running there is slight movement back and forth of the front half of the tensioner. Hence the flanged head of the bolt is under some pressure, so with time the top part has worn/rusted away allowing the tensioner to move with the force of the spring from the vertical.
This in turn puts strain on the belt and has lead to the collapse of the viscous fan bearing.
The bearing is removed by a special tool, that amounts to a steel tube with a plate that has a hole in it, fixed at one end. A bolt is passed through the rear of the bearing and the steel tube is mounted on the front with a nut. The nut is then turned to draw (pull) the bolt and hence bearing, forward and out of the mounting bracket. That’s the theory; in reality the bearing would not move. We went through a couple of threaded rods/bolts trying to remove it. The bracket that the bearing fits into-photo: 8, carries the alternator, power steering pump, fan, tensioner and water pump. The water pump is mounted to the bracket or should I say into the bracket see Fig1 No.4, so the bracket becomes part of the cooling system with water inlet/outlet pipes and thermostat.
As the car had fresh coolant from not so long ago we did not want to split the system (from what I can remember there are recommendations in the service guide about not reusing coolant) but in the end after trying everything, we had no option but to remove the bracket.
Hence the front of the car was removed completely to give better access to the bracket. After removing the alternator, power steering pump, small timing belt cover bolt, and disconnecting the water pipes at the rear of the bracket, the five mounting bolts that hold the bracket are next. There is one small bolt that faces forward to the engine, the remaining four long bolts fit to the side of the engine.
This was where we hit our next problem as even with great care, one of these long bolts sheared off. And it just happened to be the lower rear-mounting bolt, “O joy”, or words to that effect were not spoken!
Removing the bracket now proved difficult as the remains of the broken bolt was stopping the bracket moving in the desired direction. After much leverage the bracket finally came away from the engine.
Photos: 8 and 9 shows the bracket and photo: 7, the old bearing.
In Fig1 you can see:
bracket No7,
tensioner No12,
bearing No13,
water pump No4, and
seal No6.
While in the exploded view Fig2 (top right)-
No19 is the bracket,
No7 is the tensioner,
No22 the bearing,
No9 circlip and
No4 ribbed belt.
Time for the hydraulic press, the bearing was removed by the press, although it still took some moving and I wonder how many times this happens in a dealership.
A new bearing, a set of long bolts and water seal were ordered, photo: 10.
The long bolts come as a set of four; these are fairly light duty bolts so I would imagine it is quite a common occurrence for them to shear.
New bearing and retaining circlip fitted to bracket, then a new seal, and the bracket is mounted back onto the engine.
CAUTION! The bolts that hold the bracket to the engine are tightened in a numbered sequence and to a specific torque.
Then it’s just a case of rebuilding the car. We fitted a new ribbed belt but if you reuse the old one, you are supposed to mark its direction of rotation so it goes back on in the same way. The engine was filled with fresh coolant and bleed of air. From what I have heard, it would seem that the replacement of the belt tensioner is quite common and a few viscous fan bearings have also been renewed.
Obviously age and mileage plays a part, but if you own a car with a similar set up, it would be wise to check everything is ok. Photo:11, job done
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Thanks to Donald Teare for the article. Copyright 2010- 2012 Donald Teare/ Audifans.net - reproduced with permission.
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