heinrich

CALLING PORKEN:

Make i some clear tbelt covers

PorKen

I reckon you could vacuum form the center cover, but it would discolor and/or deform quicky in the heat.

How about a stainless hardware cloth* center cover?

*Critter wire

heinrich

no mesh. give me clear or nothing

heinrich

what's that racing crap ... will it work?

heinrich

btw I like being able to call on the name of Ken and get a response in matter of minutes

ew928

Will Lexan discolor in heat. (That's the racer rear window replacement)
Thick enough Lexan will stop a bullet, me thinks.

Too bad we ain't got some of that Star Trek Transparent Aluminum.
(Whale tanked Klingon Cruiser in one of the movies)

Ernest (NYC)

PorKen

I ain't your be-otch, be-yaatch.
...

Anyone know what the difference between center covers '928 105 144 05' and '928 105 144 07'?

Just the 'Toothed Belt Warning' connector?

karl ruiter

Hmmmm
I have pretty much stayed with my OBs because the interference valves and belt system on the later cars gives me the heebeegeebees.
I have thought of re-designing the system though. For me it would be 1) a better tensioning system. One that did not have ANY plastic parts at all. Somebody said something about making some Delrin bushings, and while that does make sense, I would really like to see bearings...perferable big meaty ones...throughout the whole tensioning system. I don't care that much about how it is sprung, but it seems like a huge portion of the failures are plasitc bushings. 2) Let's not have the timing belt depend on the water pump. I mean, COME ON. You know that water pumps are gonna fail because there is a rubber seal that seperates the bearing from water, so lets not have that event eat up the motor. I had been thinking of a roller near where the impeller pully is and then the impeller being driven either by a secondary belt or gear or something, but somebody mentioned an electric H2O pump and I think that makes sense too.
I think that any of the people who are making super charger kits could make a kit to do this (DR? Carl? anyone?). If it was available for around $1000 I would happily buy it. If not I'll have to wait until I can get around it, and by that time gas will be $20 a gallon and I'll be too old to drive.

H2

Looks like PorKen don't need no stinkin' belt covers at all. PorKen, Buddy, don't bend over your engine with a tie on. It wouldn't impress anyone. Plus it might knock your Tbelt off.

BTW, Heinrich's statement "brace is not for pump - it's for that bolt that alway bends"...isn't that bolt that bends part of the drifting Tbelt problem? That is, the brace from the water pump braces the bolt which braces the gizmo that braces the belt...or am I thinking of the wrong bolt? I gotta go to bed, thinking's killing me. If PorKen can't fix it nobody can, me thinks.

Seems like these plates could be punched out and formed pretty easy but it would take an engineer to get it right. Clearance of the tbelt covers may be an issue.

Harvey

H2

$1000 for a failsafe belt system (minus the rubber breaking on its own) would be a good deal I would think. If proven, what peace of mind. Then again, I'm not sure I want to be the Alpha or Beta Tester. Great idea.

Harvey

heinrich

Harv, the boss bolt that is centre of the big roller, bend and btw more often, wears badly (even the bushings can be OK but the steel can be very bad).

Ken, sup **** .... 03 is 85 euro; 04 is 87 S4. Don't know the others.

Ernest, ain't no thang ... discoloured wil still be trnsparent ... better than now

SharkSkin

Just replacing the bushing with a bearing might not be such a great idea. Bearings are meant to rotate, and I would think that the bearing would have to be way oversized to compensate for the prolinged vibration over such a small contact area. Are you ready to try welding a bigger boss into the tensioner arm to hold that bigger bearing? If so you may have something.

Perhaps it would be easier to replace that shoulder bolt that bends with the next size up. Adding material to the boss that it threads into might be needed, but the bigger bolt would have much more strength. The key there is whether the arm can be reamed out to the correct size for the larger shoulder without weakening it. Anyone have one in-hand that they can measure/photograph with this idea in mind?

Garth S

Regards the pivot bolt (< '87) or the pivot stud (> '87), the diameter of the bearing surface is 12mm. The hole diameter in the carrier arm is 15mm, leaving the max. wall thickness of the bushing @ 1.5mm.
Firstly, the perhaps simplest approach to the bushing is to press in one turned from phosphor bronze: this material has served in small electric motors, alternators and starters over the years . If it can survive the side thrust of a starter's Bendix drive, possibly it could handle the small arc of rotation and 'twist' seen by the carrier arm. Who is the materials expert?
My expressed concern over a bearing is shared by Dave - but I don't know enough about their service specs to say otherwise. The carrier arm pivot bolt hole has as little as 3.5mm wall thickness ( up to 4.5mm) ... leaving little to machine for a bearing in any event.
Secondly, the 12mm pivot is not the problem ... it is the reduction to the thread diameter at the shoulder: the pivot bolt has 8mm threads, and this was increased to 10mm for the S4 pivot stud. Why live with this reduction?
If one really wanted to stiffen this unit up, we need a pump boss that is capable of accepting a 12mm thread ..... try to bend that !!!!!
If that is not enough, and a suitable bushing material could survive at 1mm wall thickness .... then a 13mm stud could be fitted .

So, any votes for a M12 thread on the pivot bolt/stud that slides in a bronze bushing?? Edit ... on reflection, in this service, the Nylatron is probably superior
The pics are self explanatory - the bushings shown were the first 'interference fit' ones turned from delrin.<-- wrong! Edit .... they are of black Nylatron, a molybdenum disulfide filled nylon .... I used the delrin on a BMW project ..

heinrich

Garth / Dave, the boss/bolt do wear badly, so thread isn't the only issue. How about high tensile steel? It should remain inregritous far longer, and thus the bushings should last far longer.

Garth S

True - but why do they wear? In my very small collection, the pivot bolt wear has been on bolts and bushings that were as dry as the Sahara, but had shown prior signs of rust: it appears that rust enbedded in the bushing acted as an effective abrasive on the parent metal. A corrosion/errosion sequence would be one mechanism ... that is why I pack the cavity with a high tack grease - to keep any water out, for that would be the root cause were this true..

Actually, that pivot bolt in the pic above is a dead soldier, for it already has some errosion .... as can be seen.