300 Tdi belt tensioner and the dime!

Maybe I was just unlucky with the coin? Could it be argued that because the back of the tensioner is in fact webbed and recessed across its face that there is little friction advantage when bolted flat to the block - therefore a coin makes no difference in respect to friction holding? I still suspect an engineer might say flat is best even with webbing.

I read this thread because I to am having a frustrating time with a belt/bearing squeal in a disco 1 (not the one I mentioned earlier where the tensioner broke loose - after the broken bolt fiasco I put a new unit in that vehicle and have had no issues). The noise is coming from the tensioner-to-water pump area - not the alternator, powersteering pump or anywhere else. A spray of lanolin on the belt makes the noise go away for a few minutes, which indicates to me it is a belt misalignment problem and not a bearing noise.

The water pump is new, the viscous fan bearing is new, the idler bearing is new, the tensioner is new (and I've replaced the new bearing with another new bearing, moly greased it etc, also swapped the rolling wheel with others). I've installed some of these units on other discos and never had this problem.

Yesterday I tried putting feeler guages behind the tensioner to determine the amount of misalignment. I got up to 1mm without any change to squeal before giving up - after all this is a new unit and shouldn't need much adjustment (if at all).

When in frustration I took the tensioner off for about the 15th time, I noticed that the lip around the bolt hole, on the engine block, was slightly depressed and distorted.

I put a straight edge on the back of the tensioner to find that the hollow bolt, holding both parts together, actually protrudes about 0.5-1mm past the back ie the back is not perfectly flat, and hence the distortion around the bolt hole.

I filed down the protrusion and reinstalled the tensior. Initially I got a 90% reduction in the chirp - went to intermittent rather than constant. When revved up, not noticeable at all. Ran for about 10 minutes like this. Restart the vehicle a little while later and the chirp is pretty much back as before any attempted fix!!!

Looked at the teflon disc that separates the two halves and it does seem to be slightly tapered ie just slightly thinner on the drivers side than the passengers side (when it should be uniform thickness when new).

Has the apparent inability of the unit to bolt flat in the first place allowed an imperceptible wobble in the whole unit leading to undue wear on the teflon bush?

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

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Originally Posted by workingonit

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

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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.

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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.

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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.

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Originally Posted by workingonit

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

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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.

Oh, and I think Steve may be correct about bearing deflection, which in turns puts pressure on the moving arm , which in turn puts uneven pressure on the teflon ant-friction pad. They all seem to go thin on the drivers side and stay thick on the passenger side. In an exaggerated sense there is some force moving the arm toward the radiator. Why? If there were some randomness in which way the force generally apply, then you might expect as many arms to move to the engine as to the radiator, and as many cases of the passenger side of the teflon bing thinner than the drivers side.