Gary Knox

--------------------------------------------------------
Popcorn for sale, Popcorn for sale, Popcorn for sale. Get it while it's hot and well buttered. Salt on the side table beside the napkins.

Gary

hacker-pschorr

Jerry Feather

Now I wonder why we don't just find a nice heavy duty spring that fits in there and replace the spring discs.

Speedtoys

Because it's not a 'spring' Jerry..at least in the sense of "a device to apply constant resistance". The OE unit resolves belt flutter, which causes can timing to float...I've -seen- it.

It's more complicated that that..and FWIW, simple to maintain.

And a set of washers is <$300.

https://www.porschemarinparts.com/oe...te-92810553902

Jerry Feather

You know? Jeff might just be correct in spite of the fact that the link he gives us shows clearly that their other name is "Spring Disc." I kind of thought about being sarcastic about that, but what catches my attention is the word "bimetal." I use bimetal band saw blades because they are strong and the stay sharp forever, but I think that bimetal means something else. Here I think it refers to the discs being made out of two different metals, and where I have seen that before in this kind of context is where change of shape with temperature is somehow desired. Here I suspect that these discs are intended to change shape one way or the other with the temperature of the engine. That also, at least for me, kind of clears up the question I have always had, and that is what is that stupid heavy oil in there for. There is so little friction between the discs that is has no lubrication purpose; but now I think it is merely there to transfer the engine heat to the discs.

I now think that when the engine heats up it grows a little bit and that changes the tension of the timing belt. Thus when the belt gets tighter (I suppose) the discs change shape in order to match the position of the tension roller to meet the new belt tension.

Actually aside from all of that and in regard to the OP's question, If it were me I would discard the broken pieces of disc and put the tensioner back with one disc short. The reason for my idea is that when I bought my first S4 I had driven it about quite a bit including the long trip to bring it home at the start. Then I decided to change the timing belt because I had no data about when it had been done before. When I did I also overhauled the tensioner. What I found when I did that was that the discs were arranged in a very random fashion with no rhyme or reason to it. I did the research and found the arrangement in opposing groups of 5 and put it back together. It was also very dry by the way. Nevertheless the tensioner originally functioned just fine and it has of course done so afterwards ever since.

As to the potential for any or many more of the original discs failing, I would expect that if they do and if that becomes a problem it will show up with the warning light being lit. Then I would either buy the $300 set or even just replace the latest failed ones. In this regard, and as Greg kind of suggests, I suspect that no one else has ever seen a failed disc; so I suspect that there was simply something different and faulty about that particular one rather that age acting on all of them.

Eidt: Aside from that and to the extent that the adjusting screw might still need a full configuration of discs, which I strongly doubt, but if the missing disc is a problem I would actually follow Roger's suggestion and simply replace it with a fender washer.

FredR

The Belleville pack functions as a linear spring - the bi-metal washers function to cause the pack to shrink in length as the engine heats up and thus keep the same tension [more or less] irrespective of the temperature the motor is at. The belt tension alarm does not arm for three minutes which is about the time it takes to get the thing to warm up a bit and presumably get into its "comfort zone". .

The washer pack make up is required to achieve the design spring rate - in the case of the later models the spring pack acts with a composite spring rate equivalent to 0.6 that of one washer. Start omitting washers and the design intent will be compromised but whether it would be any consequence is another matter altogether.

Jerry Feather

Point .06 is about a sixteenth of an inch. Divided by 35 or 40 discs that is about one thousandths in tension roller displacement. Missing one disc is of almost no noticeable consequence.

Speedtoys

The tensioner also seems to work in a way that is complimentary to the unique belt system physics...it 'captures' and removes the belt flutter. Dont ask me how..but I saw it between two different tensioners, from cold starts, steady throttle and rolling into and out of the throttle. Maybe the choice of oil IN the tensioner dampens these transitional requirements in the belt system? I do not know.

Also..missing one washer, is going to change how then tensioner works...so no, I would absolutely NOT do this. You can make up for tensioner length with a bolt, but not tensioner....tension and damping action. It will be weaker.

I dont have the non OE videos..I thought I had em, but when I got home, I screwed up, nothing was there..but here is how QUICKLY from a cold start the OE system works, it seems to take very little heat from the block to the oil, to the flooded washer assembly to start to work:

Other interesting info:
https://www.pfeiferindustries.com/tr...ting/vibration


Has anyone wondered how MUCH pressure is applied by the OE unit? Seems to be a common discussion topic in these three articles. I would imagine pressure/rate/and how "fast" it "reacts" to quickly changing tension is all science that some German nerd knew but failed to write down for us.

Jerry Feather

AH, HA! There is a lot more unknown in this topic than I thought there might be including whether the Spring Discs are in fact springs or not. And including the fact that Jeff said that these discs do not provide constant pressure as with a spring, but now he is talking about them applying constant pressure. WTF.

Speedtoys

Dont think too hard.

They are springs, but they are temperature dependent....

Think about the design, not the words.

Jerry Feather

OH!

Jerry Feather

It appears to me that the Factory reduced the number of discs from 40 to 35 and they are all the same discs. Then they put in a spacer. I am suggesting that the OP reduce the number from 40 to 39 and if needed, I and Roger suggest a fender washer as a spacer, but several of you are waving the caution flag. DUH!

Speedtoys

When the WSM tells me to install ducking garden hardware into my timing belt tensioning system, I'll do so.

Jerry Feather

Yes, I have a pretty good idea what you will do and when.

GregBBRD

Please don't confuse people with your fact based agenda,
especially when using buzzword terms like "belt flutter" and "cam timing stability."

There's never any room for details like that, when dealing with emotion instead of reality.
"Because a random parts guy said it was the hot ticket, I bought it. To he!! with the mechanical people who actually took the time to test it!"