AudiWorld Forums

AudiWorld Forums (https://www.audiworld.com/forums/)
-   A8 / S8 (D2 Platform) Discussion (https://www.audiworld.com/forums/a8-s8-d2-platform-discussion-8/)
-   -   cam chain tensioner shoe - can it be improved? (https://www.audiworld.com/forums/a8-s8-d2-platform-discussion-8/cam-chain-tensioner-shoe-can-improved-2814275/)

gOOOOran 10-03-2011 12:24 PM

cam chain tensioner shoe - can it be improved?
 
I was just wondering can these be made from better material. I realise the current nylon ones do last a long time and rarely break, but I would still like to replace them when I do a cam cover gasket change some time in the future.

Anyone know of a better plastic that doesnt become brittle with age?
Would aluminium be a bad idea because it would have a steel chain running over it and generate aluminium dust into the oil?

They can be bought on ebay and given to a company to cast them from some other material.

http://cgi.ebay.com/ebaymotors/AUDI-...m=180459408601

silverd2 10-03-2011 02:24 PM

Don't believe ANY type metal would work.
...and can't really comment on the type of plastic or composite that would be best, because there is VERY little info available to the public on exactly what material is used for the original or replacement pads...believe me, I've researched this.
And I've thought about a better design a lot after doing a pad change myself (passenger's side...haven't gotten to the other side yet). The combination of friction, heat and oil contact presents few choices with the design I observed in my '01 D2.
I believe that the only improvement to the pad design (may already be in some engines?) and maintaining low friction, quiet operation, is to replace them with cogged gears riding on oil bathed journal bearings. This would increase complication, expense and definitely the size of the tensioner, but could potentially last "forever".

Changing the pads is no small job...tensioner must be removed to change upper and/or lower pads. Passenger side is subject to some short cuts, since it's on the other end of the head from the belt...I proved it..see link below. Still no small job, but doable without all the steps laid out in Bentley.
Haven't gotten to the driver's side yet (and will "publish" when I do), but looks much less likely that I can skip steps to get that one out, due to it's location.

http://forums.quattroworld.com/a8/msgs/55496.phtml

gOOOOran 10-04-2011 04:27 AM

1 Attachment(s)
Thanks for the excellent post of how to replace it. Its usefull to see how it looks inside the engine.

I came accross this forum in my brief research so far:
http://www.eng-tips.com/viewthread.c...=292501&page=1

The interesing thing is that the ones I have seen people taking out of engines that broke always appear black or dark. Could it be that these are made form Nylon 66 (graphite filled) and that the new creamy colour ones are the Nylon 46 ones which are more durable? Or is it that the old ones are just discoloured from oil?
Certainly the part number has changed when you order a new tensioner unit from Audi indicating they have updated something.

It would be really interesting to find out if Audi have changed the pad material. I wonder if anyone has a contact at the factory that could confirm this?

An option I am considering is to have a steel or aluminium casting made to the shape of the pad, and then cut down the bottom of the pad and insert it into the casting, so that the chain still runs over the plastic surface which is now embedded in a metal cradle, so even if the plastic cracks there is really no way for it to fall off as the chain is pressing on it from one side and the metal cradle holding it in from all other sides?

Or maybe a thin 1mm steel bracket all around the edges of the pad would do.

Something like in the attached picture.

gOOOOran 10-04-2011 01:00 PM

another interesting link. These guys make the stanyl nylon 46, I wonder if Audi get the new chain shoes from them?
http://www.dsm.com/le/en_US/stanyl/h...properties.htm

silverd2 10-14-2011 05:15 PM


Originally Posted by gOOOOran (Post 24206160)
The interesing thing is that the ones I have seen people taking out of engines that broke always appear black or dark. Could it be that these are made form Nylon 66 (graphite filled) and that the new creamy colour ones are the Nylon 46 ones which are more durable? Or is it that the old ones are just discoloured from oil?

For all it's worth...here's a photo (below) of a cross-cut I made on one of my old pads. The interior is exactly the color of the new pads I installed. Testing with a pick, the interior cream color is still soft, while the aged oil darkened exterior is hard and brittle.

Starting on 2004 (D3) models, the tensioner number changed a little...ends with a "P" instead of an "E". If you look at the photo of the "P" model in the ECS link (only model sold new now...fits all 2000-2006 models), the pad material "looks" the same. My hopes, for future replacement reference, is that the "P" model has an improved interior design that limits start-up noise due to insufficient tension before oil pressure builds...the very thing that I firmly believe leads to breaking older (more brittle) pads...that's the side that broke on mine...the tensioner that always made start-up noise.

Ignore the price..EVERYONE sells OEM parts cheaper than ECS...more like $520-545 elsewhere:

http://www.ecstuning.com/Search/077109088P/ES261671/

http://i1217.photobucket.com/albums/...aterial024.jpg

gOOOOran 10-16-2011 03:32 AM

Thanks for taking the time to do this. That is really good to know, I was very curious if they changed the material at some point. Now it looks like the material of the plastic shoe is the same, just gets stained over time.
I definitely want to chage mine soon, I'm at 110k miles so they must be pretty worn by now. I'm sill thinking about asking a company that does automotive steel stampings to make some 1mm thick (or thinner) steel cradles that hold the pad, so that even if it brakes the pieces stay in place and continue to support the chain. I found a company in the US that I would like to contact, but cant find the link, I'll post it up as soon as I find it.

gOOOOran 10-31-2011 04:46 AM

more info, I got a reply back from DSM who make Stanyl Nylon 46

"Thank you for your enquiry. DSM produces Stanyl plastic granulate as a raw material, we do not ourselves mould any parts. Our various materials are used for a wide range of automotive applications, although not for the cam chain tensioner guide shown in your photograph.

I can only suggest that you contact a company like Quadrant for a stock shape, and have this machined to the correct dimensions.

http://www.quadrantplastics.com/eu-en/products/machinable-plastics.html"

Interesting stuff. I'm now thinking I would like to get hold of some Stanyl Nylon 46 or the new version Stanyl Diablo (glass reinforced?) and get a good machine shop to make some tensioner pads from it. Saves the hassle and hopefully expense of getting a steel or aluminium brace designed and made for the pads.

raw material can be obtained from here:
http://www.quadrantplastics.com/eu-e...-00000016.html

Are there any chemists amongst us, it would be interesting to find out what material the original Audio OEM pads are made from. (I suspect Nylon 66)

gOOOOran 10-31-2011 04:50 AM

a bit more reading:

http://source.theengineer.co.uk/mate...389668.article

pocketchange 11-02-2011 08:28 AM

Service Life
 
What's the service life of the piece?

I ask in lieu of production numbers that would need to be generated to validate production.

Sometime it simply is not worth the effort.

If the 80,000 mile service limit (per Audi) for the timing belt is achieved, isn't this a part of the assembly and the timing belt service (along with the other stuff)?

silverd2 11-02-2011 02:19 PM


Originally Posted by pocketchange (Post 24218945)
What's the service life of the piece?

I ask in lieu of production numbers that would need to be generated to validate production.

Sometime it simply is not worth the effort.

If the 80,000 mile service limit (per Audi) for the timing belt is achieved, isn't this a part of the assembly and the timing belt service (along with the other stuff)?

The point is that this should NOT be a "perishable" part, like a belt. Audi will NOT replace the pads for you...they won't even sell them...only the entire tensioner, even if it's still operating properly.
It's a part that did not even exist on A8 engines until the 2000 & up 40V motors. Not unusual that added complication, to get more power and a greater spread over the rpm range, would add expense and another possible system failure, but in question here is the material (and design) used in the highest friction part of the system.


All times are GMT -8. The time now is 02:54 PM.


© 2019 MH Sub I, LLC dba Internet Brands