cam chain tensioner shoe - can it be improved?

[gOOOOran]

as silverd2 says, we're having to replace or re-engineer a part (buried in the engine) that Audi should have engineered properly from the correct material in the first place. I have had further communication, the company Quadrant has several other materials that may be better than Stanyl 4.6 They wont make a mould for fewer than 100,000 parts, so thats out. They do seem to be willing to machine parts from a drawing, no probs I can do a drawing for them. Of particular interest was this material Duratron CU60, sounds like really tough stuff, I think I'll ask them to machine it from that if its not too expensive. http://www.quadrantplastics.com/eu-e...ron-R-pbi.html

[gOOOOran]

I forgot to add, it looks like it was possible to buy Stanyl 4.6 (also called Nylatron?) from ebay. Incase someone wants to machine the parts themselves.

http://www.ebay.co.uk/itm/NYLATRON-4...-/380366605182

[gOOOOran]

I have another sneaky idea. Someone out there obviously has a mould and casting capabilities for the chain tensioner since we can get these parts from ebay.
If we can find out which company this is, maybe we could persuade them to do a limited run using higer quality plastics like those mentioned above.

[gOOOOran]

material mystery of the original parts solved!
the ebay pads, which are cast from the original Audi pads, have two codes cast into them on the underside. One code is probably a part number,
10.100472

the other code is:
PA 4.6

this is actually a material code. this is actually common automotive practice with plastic parts, I beleive the bumbers also have imprinted on them the plastic type they were cast from.

Searching on the web for PA 4.6 reveals this is actually PolyAmide 4.6 or Nylon 4.6, so the original Audi pads are from the heat resistant Nylon 4.6 we were discussing before.
Unfortunately this means that the Nylon 4.6 material is not good enough for these engines as it decays and loses its properties after approx 100k miles as proved by Silverd2's S8 and another S8 in the UK which had its pads brake at a similar mileage.

For me this means that a better longer lasting material has to be used, I'm hoping Duratron CU60 from Quadrant Plasics is the right material, I need to prepare a drawing for them to machine from, and then I will order some pads and happily guinea-pig my car to see what happens.

[silverd2]

Originally Posted by gOOOOran

Unfortunately this means that the Nylon 4.6 material is not good enough for these engines as it decays and loses its properties after approx 100k miles as proved by Silverd2's S8 and another S8 in the UK which had its pads brake at a similar mileage.

*Ahem*...that's "silverd2's A8"...by choice, not a compromise. My favorite of all the D2's is the FL A8 SWB, which, following many test drives, was the target of my nationwide search. I bought it at only a little over 3 years old with almost 3 yrs of remaining CPO warranty.
If max power and quickest handling was the priority, I'd have stayed with Porsche...the S8's mpg's, higher rpms and firmer ride sort of defeated my purpose of switching to a 2-ton 4-door luxo-cruiser. For my tastes, didn't like the feel of the S8 for a daily driver and the extra length/weight of an A8L didn't make sense.
NO offense...2 different excellent cars...neither better than the other...different tastes.

ANYWAY....Yes, Audi dropped the ball on the tensioner pad material. Belts, filters? ...I can see. But, even at 100K miles, an internal engine part should NOT be a concern due to poor choice of material. There was plenty of research and real world data to rely on, from past engines, including motorcycle engine designs...not "new" tech by any stretch. Kind of inexcusable for what otherwise could easily be 1/2 million mile engine.

[aduggs]

Just looked up Polyamide Type 46,(Super-tough) material in my engineering CES EduPack.

One of the thermal properties was surprising to me:
Maximum service temperature is rated at 93-107 degrees Centigrade.

Also, the melting point is 306 degrees Centigrade.

Common uses: Gears, cams, rollers, combs (lol, low friction), kitchen utensils.

The max service temp is low for a friction part. Being a mechanical engineer myself, I would not have chosen this material (leave it to the Germans).

[gOOOOran]

apologies Silverd2!
I forgot that your car is a A8, thats a fine car as well and has certain advantages over the S8, especially the A8's 5th speed gearing which is much better than the S8 which revs close to 3000 at 70mph.

Aduggs, thanks for the additional info, as you point out that is a unsafe maximum service temperature considering it is almost identical to normal engine temperature. Really odd choice by Audi.

[pocketchange]

Is the cam tensioner the part being adjusted by tool #3366?

If so, why that design? Couldn't another sprocket replace the nylon(?) pad?

[aduggs]

Ideally, you would have an idler sprocket attached to a spring/damper system taking up all the slack in the chain, but there is not always room to fit in a sprocket with enough teeth (taking into account teeth pitch angle etc.) This would be my guess as to why the engineers did not use this in the first place.

It is common to use low friction materials to remove chain slack, but they do wear out (as all parts do).

The problem I have with choosing Polyamide Type 46, is that it has a low service temp, and also I just noticed that it is rated as "Good" against organic solvents. It should be rated "Very Good" or "Excellent" to be considered for this application. Since this part is covered in engine oil (which is/contains organic solvents), it will deteriorate. This is why you see the discoloration on the outside of the shoe in the pic silverd2 posted.

[silverd2]

Originally Posted by pocketchange

Is the cam tensioner the part being adjusted by tool #3366?

If so, why that design? Couldn't another sprocket replace the nylon(?) pad?

Look back at post #2 on this thread...great minds