ROG100

Judging by the fact that the mass of failures of cam gears caused Porsche to redesign them and the fact that we sell lots of them at circa $400 each I do not think that is the norm.

Hardcoat, or any anodic coating, is strictly a surface enhancement. While thicker, hardcoat is still aluminum oxide - a brittle, ceramic like SKIN that makes the surface more abrasion resistant, but in metallurgical sense, actually weakens the material - lowering the fatigue strength (this is why thin Type I chromic anodize is preferred over thicker Type II sulfuric anodize). Basically, the thicker the oxide, the more degradation to the materials fatigue strength there is. If strength is what you need, consider an alloy change - 7075 alloys are stronger than 6061 alloy is stronger than etc. Beauty is skin deep but doesn't give one a clue as to how strong one is!

Looks like they copied the old gear 928 105 530 01 and not the later gear.

A great price for those who do not cover many miles.

Red Flash

Roger, I have a pair of your of your cam gears (I think from about 2012) still sitting on the shelf. What material were those made of? They look beautiful, but I have not needed to install them yet.

M. Requin

Pretty much confirms what I said, but strength is not the issue, hardness is, which is the factor which controls wear. And the 7075 alloy series (also the 2341) is MUCH harder than the 6061 series- take a look at Machinist's Handbook for an easy ref. After the new wears off (slang reference) it's what left that counts...

And the sprockets that you briefly supplied (I think I got the last pair), are absolutely top notch in terms of finish- beautiful work! And I am only guessing they are 7075 (but it is a semi-educated guess).

jeff spahn

Yes, I do too, still in the bubble wrap

tarzibach

Roger, I don't think you have the right idea about anodizing, especially type III. I found a fairly simple explanation of it here: http://www.d-chn.com/processes/conve...zing-type-iii/

Besides that, hard anodized 6061-t6 is the industry standard for performance cam sprockets/ timing pulleys. ie: Lindsey Racing, AEM, Blackwork, tomioka racing...

ROG100

Look I do not profess to be a metallurgist by any means. However when Porsche engineers decided the aggressive wear on the 6061 cam gears was not acceptable they changed to 7075 with a hard anodized surface treatment. This change was made specifically to stop wear on the 32v 928 cam gears - period.

My statement above still stands and I do know what the hard anodizing process is. The "simple" statement in your link does not change that at all.

I spent a lot of time talking to the cam gear manufactures some of whom you mention above. They suggested 7075 just like Porsche.

There is one thing you can't get away from and that is Porsche never did something unless it had a very good reason.

That all been said if you wish to use 6061 and save some $ then good for you. In this particular case, I for my cars, have decided to bite the bullet once and know they will be probably the last pair I ever buy for that particular car.

Each to there own.

hacker-pschorr

This is where your information is flawed.
The original cam gears are not machined billet 6061 like the ones posted here, the are cast. This is a significant different.

When comparing the structural strength of 6061 vs 7075 you are 100% correct, 7075 is harder which is why it's impossible to weld. However, the last time I checked the issue with cam gears failing was not their overall strength (cracking, braking apart etc...) it's the surface wearing. This is where the hard anodizing come in.

When you hard anodize 6061 and 7075 the wear properties are the same. Who says? A friend of mine who specializes in anodizing at a large industrial coating facility here in Green Bay who mostly does work for the military.
In fact, anodizing strengthens aluminum, making billet hard anodized 6061 significantly better than original gears.

Once you hard anodize aluminum, if the coating wears off then yes..... 7075 will last longer than 6061 but both will fail in this application without any coating. So the difference is moot.

Why did Porsche choose to go with 7075 for their now gears? Frankly I don't care, the reason "Porsche did it" doesn't fly with me. This is the same group of people who designed a water cooled flat 6 with a sealed bearing on the main shaft with no easy way to service it.

One advantage to 6061 is weight, it's lighter than 7075. This may be a non-measurable difference with cam gears though. I don't know what the new 7075 gears weigh.

ROG100

I never said they were machined or cast. The 01 gears on my desk certainly look machined - they could be cast and finished machined. That would make sense as the originals were not anodized but had a spray on type of coating. I assume you can't anodize cast 6061.

Based on everything I know I have made my choice. As I keep repeating - your money and your car you make YOUR choice.

My point about the anodizing process weakening the base material still stands. In reality the factor is very very small so mute in this application.

Please go ahead and buy your 6061 cam gears.

M. Requin

Not quite. First, it is not impossible to weld 7075, it is just difficult, and that is not because it is hard, it is because of the composition of the alloy.

That is simply not so. Take a look at Machinist's Handbook. 7075 is a considerably harder material, period, no matter the surface treatment.

"Non-measurable" for sure- again, take a look at Machinist's Handbook (or any other reference).

V2Rocket

can't help but wonder if steel 944 gears could be made to work on 928.
obviously would have to change the crank sprocket too since 944 have fewer teeth...anyone have a 928 crank drive sprocket they could measure thickness and shaft bore diameter?

hacker-pschorr

Ok, but you did say: "However when Porsche engineers decided the aggressive wear on the 6061 cam gears was not acceptable" this implies a comparison to the gear presented here which are billet 6061 and hard anodized, not cast with some unknown spray on coating.

Sorry if I mis-used the term "hard" here, it's irrelevant since no welding is needed with cam gears.
Anyway, the welder I spoke to which said "impossible" has welded titanium, inconel and successfully repaired many 928 blocks. When he said impossible he was most likely simplifying the difficulty in doing so since if anyone can do it, he could. I didn't ask for a direct quote to be used in a public forum, so my bad there.

You are missing the point and I don't have to read a handbook, I'm talking to actual machinists with 3+ decades of experience. Read all the handbooks you want, nothing replaces actual real world experience.

Bottom line, no matter how much harder 7075 is, you cannot run it without some kind of coating when used in this application. When you apply the same hard anodized coating to two identical gears, one 6061 the other 7075, the hardness of the material is irrelevant since it will not come into play until the coating is worn through. If that happens, both will eventually wear out.
So the bottom line is, what is causing your coating to wear out? Fix that problem if it's such a concern.

Nope, whomever provided you with this information is wrong. Sorry if my local chemist friend at Pioneer Metals overseeing their anodizing and plating process disagrees with you. His response to the question does anodizing weaken or strengthen aluminum:

"Strengthens. Anodizing creates aluminum oxide, which has a stronger crystal lattice than raw aluminum. The allow doesn't matter".


So I say to all of you, put your money with your mouth is and install an uncoated 7075 gear on your 928. If you insist they must be coated, you just proved my point.

SeanR

Deleted.............I just want good gears to provide customers.

V2Rocket

...for anyone who might want to check the 928 dimensions...
the 944 DOHC crank drive sprocket is approximately 1-1/8" thick (front to back) and 1-3/32" shaft bore diameter.

944 DOHC cam drive sprocket uses the same mounting parts as the 928 DOHC so that should be a bolt-on steel gear for you, if the crank sprocket fits.

Rodrv6

928S4 crank sprocket is about 1.06 inches thick and 1.57 bore...........

V2Rocket

thats a big difference in bore but there's definitely the meat there to hog it out if needed.
or, maybe the production could change to make suitable crank drive sprockets and just use 944 cam gears that are readily available (like $40 new for a steel one).