Thread: 300 Tdi belt tensioner and the dime!

Originally Posted by workingonit

Interesting to see what other get when they put a straight edge across the back of the unit.

Wow, I'm heading overseas tonight. When I get back I will take mine apart again and run a straight edge over everything. Let's get this one nailed.

Something I noticed when I did mine. Before inserting the washer, the tensioner pulley ran perfectly "straight" with the engine running. No sign of any wobble. When you have a feel of it on the bench there is noticeable movement in the bearing (normal). After the washer was inserted and the chirping silenced, I could see a gentle wiggle of the pulley as it ran. To me it indicated the pulley had significant side load prior to keep it running straight.

Steve

Sometimes it can just be a temperamental belt,try a new Dayco one.That's if you have not already replaced it!

I've noticed, as Steve has, that the bearing has some play. However, I've been accepting of this level of play as it is a simple bearing - past reading of manufacturers information seems to confirm this - and swapping new bearing for new of different brands has made no difference . And these bearings give no probs on the other Disco's I have.

You guessed right eddy, different brands of belt have been tried. From memory the Dayco did run quiet for a while but the chirp came back. I've also very carefully cleaned all pulley ribs, removing any embedded bits of rubber etc.

On my other vehicles I've notice that over time some tensioner wheels can wear in different ways, the surface finish becoming concave or convex rather than remaining flat (I doubt they were manufactured that way, but happy to be corrected).

I'm going to order some parts today and see if my regular supplier has a couple of brand options for the tensioner, focusing on a flat back.

Originally Posted by workingonit

I've noticed, as Steve has, that the bearing has some play. However, I've been accepting of this level of play as it is a simple bearing - past reading of manufacturers information seems to confirm this - and swapping new bearing for new of different brands has made no difference . And these bearings give no probs on the other Disco's I have.

You guessed right eddy, different brands of belt have been tried. From memory the Dayco did run quiet for a while but the chirp came back. I've also very carefully cleaned all pulley ribs, removing any embedded bits of rubber etc.

On my other vehicles I've notice that over time some tensioner wheels can wear in different ways, the surface finish becoming concave or convex rather than remaining flat (I doubt they were manufactured that way, but happy to be corrected).

I'm going to order some parts today and see if my regular supplier has a couple of brand options for the tensioner, focusing on a flat back.

You've probably already done it, but I found squirting a bit of water on the back of the belt just prior to the tensioner pulley will silence the squeak if the pulley IS the cause. I found it a good troubleshooting tool, and doesn't leave any residue.

Steve

Thanks Steve, I will try water directly behind the tensioner wheel when my son gets home with the vehicle this arvo. To date I've been hitting the belt ribs with some lanolin spray, which silences things for a while, but I guess some spray could be getting on the un-ribbed side and giving me a false lead as to what is really squealing.

MRAuto are sending me a Dayco unit, and have put a straight edge across the back and find the hollow bolt is flush or slightly below level as you should expect. Not overly confident, but we shall see!

I would really like to understand the engineering principles behind why this method of tensioning is used, and as to whether you could resort to something more conventional (putting aside where you would actually fasten something).

After all, the timing and aircon belts are tensioned conventionally, but are they subject to the same forces? The larger the pulley the quicker the surface moves per rpm.

The timing belt operates off a much smaller diameter pulley system. While the aircon belt is smaller in length and width but thicker than the serpentine they both work off the large crank pulley.

Originally Posted by workingonit

The larger the pulley the quicker the surface moves per rpm.

If you are talking about a tensioning pulley, then the speed at which the surface moves is not related to the size of the pulley. The surface moves at the speed of the belt. The larger diameter reduces the revs the pulley has to do, so that should be easier on the bearing.

Maybe you didn't mean what I think you meant.

vn205, the way I see it rpm dictates the speed of the crank pulley (harmonic balancer), which by its diameter influences the speed of any attached belt, (and your point) which in turn influences the speed of the tensioner wheel (moderated by its largish diameter).

The aircon and serpentine belt are both driven by the crank pulley and therefore are moving at the same rate of (say) kilometers per hour. Yet the aircon uses conventional tensioning, while the serpentine uses an adjustable/moveable tensioner.

Is the adjustable serpentine belt tensioner used because there are more accessories driven by the belt and more pressure is required to keep the belt from slipping on the many pullies? I would think the airconditioning pump, when on, would provide significant resistance and just as much chance of slip, yet it uses a conventional tensioner. Belt cross section makes a difference?

Is the adjustable serpentine belt tensioner used because there is considerable deflection of the belt once under full power? I assume the belt does not stretch when under acceleration. I would assume if we used an adjustable tensioner on the aircond belt we would see similar levels of deflection. So why one method over another?

The adjustable tensioner applies considerable force, even when the belt is not moving. You would think tension is evenly spread across the serpentine belts circuit when not moving - and why would it change?

Does the serpentine belt tend to bunch at ancillaries that require more driving force, and move more easily where driving force is less?

So over the crank--viscous fan the run is slowed - but from water pump-alternator- power steer the run is quicker - the tensioner arm lifts under power - tension is no longer uniform around the circuit. Does the force of the tensioner tend to reduce potential bunching, pulling the bunching through as the crank pushes? Dropping the revs, returns uniform tension reducing bunching(?) lowers the arm.

If you managed to put a conventional tensioner onto the serpentine belt, where would you set the wheel - at the lowest point of the adjustable arm, mid point of adjustable arm, or at the top of its range? Conventional tensioners tend to be set at the lowest point, exerting reasonable force and presenting the most resistance to movement (none at all), but still requiring some defelction of the belt under finger pressure. So set conventional at mid point of adjustable tensioner?

In making my reference to 'the larger the pulley the larger the force' I'm thinking of those forces as they are transmitted at the crank. The timing belt is on a smaller diameter pulley, when compared to the diameter of the harmonic pulley which drives the aircon belt and serpentine. So planting the foot has, to my way of thinking, far less effect on the timing belt (in terms of the distance it has to travel in a given time) when compared to the force on the other belts (which have to travel a greater distance in the same time frame). Of course I'm not taking into account the resistance of the objects to be driven by the belts, nor the size of the wheels on those objects. Its more a question of what are the dynamics affecting the belt and what tensioning system suits, rather than concerns about bearings in the wheels.