granprixweiss928

So tonight while reinstalling my timing belt setup on my 81, I choose to use the new bolt that I ordered some time ago, for the tensioner arm pivot.

the part is 92810557003 but it doesnt fit in my arm.

So I realized there are different arms, up to 81 and then another 82 on.

The pivot bolt is larger diameter for the later version.

I wanted to replace mine, because I suspected the pivot to be slightly bent, the belt tracks toward the forward side of the gears. but im not sure.


is it worth to change to the later part?

who has the later arm used? part 92810554005

gruffalo

My experience is that the early bolt bends easily, and the results is a belt tracking forward on the pass side gear.

I had a bent bolt. Got a couple of used ones that Anderson from 928intl reluctantly sent me. He didn't recommend using them. It turned they were bent too.

In the end I had a lokal shop machine a new one for me, out of a stronger steel quality.

GlenL

Yes. The later, bigger pivot matches a later arm and those will work fine with the tensioner that you've got.

Jadz928

928sRus and 928Intl both sell repros (OE is NLA).

I include one as part of a timing belt service kit:
http://928classics.com/service-kits.html

Or do what Glen says, which works too.

GregBBRD

Hold on guys....there's enough "Internet Folklore" about tensioners than almost anyone can stand....let's not turn theory into fact.

Both the early model, smaller diameter pin and the later model, larger diameter pin are no different, in terms of bending. The pins always bend at the point where the 8mm threads meet the larger diameter shaft....so the diameter of the shaft has nothing to do with bending.

Correctly assembled, neither the smaller diameter pin nor the larger diameter pin will bend. Only when some idiot (who has no idea how to install the belt) gets in there with a pry bar to install the belt will the pin get bent.

Porsche increased the diameter of the pin so that they could use larger bushings, which would "spread" the wear out more, in high mileage situations. If you use the smaller pin and a new set of bushings, the smaller diameter pin will function exactly the same as the larger version....until the bushings start to wear out......way past 60,000 miles.

Try not to forget that "early model" pins, bushings, and idler arms successfully went millions of miles....without any issues. Almost all of the issues occurred after the "first round" of belt changes (by hacks).

The smaller diameter pin is not available. 928 International takes used larger diameter pins and machines them down to the smaller diameter. This makes no sense, in my mind....I think the pins should be replaced at every water pump change, with a new pin. Therefore I only machine down brand new pins, for my use.

The biggest challenge of this entire job is the tensioner boot for the early model tensioner. Both Roger and Jim Doerr carry my adaptor kit to convert the tensioner to be able to use the later model (available) boot.

mark kibort

im trying to remembrer what happened to mine, but it did bend, even break off, and from that point forward, i just made sure i had a new one on every belt replacement. seemed like a very small diameter bolt (threaded area) for the size of the surface the roller runs on. then, with the S4, they had that support bracket that boxed the structure for more strength. i dont think porsche would have done that if they didnt see the weakness in the design. I use the old stuff i had on my 84, with old water pump too, so its a different program and is a little weak in my opinion.

karl ruiter

Make sure you replace the plastic bushings as well, either way you go.

GregBBRD

I don't think any engineer would debate that changing something from single shear to double shear increases the strength many times. They also increased the diameter of the threads which thread into the water pump, making the "pin" even more robust. And then to eliminate any change of over torqueing the pin, they include a new pin with a new water pump!

I've never left the original small diameter or the later larger diameter pin in, without replacing it, when I do a water pump or timing belt. As far as I'm concerned, either version is a "one shot" part.

I still wonder if the changes were do to failures of the system on original vehicles or as a result of failures after some "dealer goon" (interchangeable with "independent repair shop goon" or "home goon") worked on the water pump or timing belt. I've never seen or heard of a failure on an "original vehicle".

GlenL

The shear across the base of the threads is the same but the bending moment is less with a larger pin.

I looked into putting in a later water pump and braced pin. It wasn't going to work for some reason...is the pump different?

About mechanics stupidity... My latest 928 came with a later arm and an early pin. The gap was taken up using electrical tape. My suspicion is that the pins yield after they're over-tightened. Relax with the torque and use some loctite.

GregBBRD

The bend doesn't occur on the shank of the pin...it occurs at the base of the 8mm threads where they join the pin.

Lo mismo.

James Bailey

More information than most can process...

mark kibort

I still have the part, (just saw it last night in my parts box of shame) now trying to remember if it broke when i was putting it together or pulling it apart. but yes, certainly with the value of that part to the system survival... it would be a one time use part! what i do remember, was how whimpy it looked for how much load it might be subjected to.

granprixweiss928

I have the new bolt, and today I bought it to a machine shop with the old one, to have it machined down. Greg didnt have any already-done-ones in stock.

granprixweiss928

got my new bolt machined down to same diameter as the old one and installed it today. the one i removed was not bent...belt still likes to run toward front side.