Jim Devine

Dumb question- has anyone taken both a new style & old style gear and had them Rockwell hardness tested? It would be interesting to see if they really are worth the increased cost,
not that these is any option at present.

Darklands

Roger,
my shop here in Germany says the same as you .He searched for a replacement for the gears and says Porsche use a special tooth divider so you need to much fabrication time.
Conclusion:Selling OEM cam gears.

Ethre

I've gotten very similar results on early (square-toothed) gears. Repeated measurements on the gears (and belts) were close to several stock tooth designs, but never quite on. I contacted a few suppliers who were happy to compare belt design to existing pulleys, but the consistent reply was "nothing like it".

Since I'm out of the country I've postponed my search, but am considering the cost to cut crank gears (being a very basic design compared to oil pump/cam gears) directly when I come home.

I'm sure you managed a more thorough search Roger, but its slightly comforting to hear that my problem is at least similar.

ALKada

I wonder if Gates could supply a different tooth belt that would free us of the current toothed gear design? Perhaps a matching length VW gear tooth match?

ROG100

Heinrich - all about volume - they probably made more VW's in one month than the circa 50,000 928's made between 77 and 95. If I ordered 5000 instead of 100 the price would tumble dramatically.

Jim - we did the full comparison of old v new - cad drawings and all. Material was defined as well as the hardness. As already said the new gears are significantly harder than the old.

tmpusfugit

One of my sideline business efforts for 25+ years has been cutting gears....not for cars but for other 1 off sorts of deals. (antique clock replacement gears) I have looked at making the 928 cam drive gears, my equipment would certainly cut the space between the teeth without issue....however, speaking of the whole job it would require equipment I don't currently own...time could be rented on other machines but the volume of parts needed just does not justify the costs IMO.

To build a complete replacement there are several problems to solve 1) fixturing to correctly position the keyway in relation to the teeth, 2) cutting the keyway itself requires tooling I don't currently own 3) hard anodization would have to be contracted via 3rd parties 4)specifications needed of the aluminum used in the current Porsche supplied part, 5)testing and inspection of replacement parts would require specifications I don't currently have, i.e. hard anodization, how hard is hard?

I can see these being a $50 gear in say quantites of 10,000. But quantites of 10, or 100, or even 500, my numbers do not work. I agree with others however that Porsche is attempting to hit it out of the park with their current prices on these....they are I would think buying them in 500 or 1000 lots...or maybe they are committing to 10 at a time, hence the ugly prices...

opps, it looks like Roger has already covered several of my points while I was writing this....it is all about volume IMO and we can't drive enough volume to really reduce the price unless we can find a near identical gear from say VW that can be easily modified, and Roger is already all over that and not finding anything...

Leon Speed

+ 1

Why not change perspective a little bit and use existing gears and make a belt to fit? Of course this means all gears need to be changed.

dprantl

That's not a big deal. Most have to change the cam and oil pump gears anyway, so there's only the crank gear left, and that does wear too.

Dan
'91 928GT S/C 475hp/460lb.ft

jeff spahn

Can't these things be milled on a CNC machine of some type based on a high res scan of an existing gear? I mean, they can rapid prototype stuff nowadays, isn't there some way to just put a blank of billet on a CNC machine, take a new existing gear, scan the thing and out comes a new gear just like it?

Speedtoys

Sure..at a cost...and the first 5 wont be perfect..and those cost.


And that still wont be a finished product.

atb

Jim, would a "retread" be an option? Basically putting a new toothed ring on a core that has had its teeth machined down. That would take out all the machining work related to the hub of the gear. Is there a reason the retread gear ring couldn't be done in steel as opposed to hard anodized aluminum?

928er

Scanning from what I learned will get you the rough diminsions of a part. The more accurate the scan, the more expensive the scanning equipment.

Even still the data has to be verified by a human, and that takes time and skill, both of which cost money.

So they make half a dozen paperweights to get it close. Then someone has to test fit the latest version on an engine, and compare to original fit.... then take it back and forth a few times with a few more versions...... at some point you get a set you can actually use... then you get them hard anodized..

Then you can start cranking out production. Good material isn't cheap either.

tmpusfugit

Adam, I have looked at doing just that. I am a bit concerned about the amount of metal that would remain on both the steel ring as well as the aluminum hub. I did go so far as to see if there was a standard seamless steel tube of approximately the required size available. Nothing at the usual / local vendors. Other sources may have something. I have not yet followed up on that..getting lazy I guess.

As far as bonding a steel sleeve on the aluminum hub, hight temp loctite might do the job. No easy way to mechanically bond the two metals. A shrink fit in thin metal is usually not a good idea, and both the sleeve and the hub will both end up very thin. How thin I need to investigate. My first opinion is there is insufficent metal whickness to "do the job" but further inquiry is needed. I have an old set of16v pulleys to mess with, perhaps I should set forth and do so?

heinrich

If we get a good process, we will never again need this work. In other words, sourcing aluminium gears is not a problem. every 928 has a set right? Just use existing cores (as is done for rebuilt water pumps). They already fit all our engines - oil pump; crank etc. I must say that the worst wear I've seen is on crank gears. The other gears tend to become sharp and cut timing belts, but the steel ones will be a different story.

Even if a set of cam timing gears is bowed, it should be possible to machine them again, and then hard anodize. At that point I'm not sure if there should or should not be a surfacing of teflon .

atb

I'd be happy to test a pre-production set on my 16v track car.
And it may be that it wouldnt be an option for the 32v engine because the exposure to big dollar damages if it fails, but on the 16v, no big deal. At least in the testing phases.