When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Well, of course, you know they do wear out, sometimes without a lot of miles. It starts as small wear spots through the coating in the center of the tooth face, some teeth more than others, so it helps to inspect the full gear. If I see just spotty wear in the center I do not replace the gear. Once the wear spans most of the width of the tooth face, the teeth start to dish significantly and develop sharp edges, and its life span is over. To have one look this PRISTINE at 35-40K miles does surprise me. Porken tensioner....hmmm...I've put them on several 928s, but the one I bought for me is still in the box. I was waiting for more long term results.
Oil pump gear, but you get the idea. Not my photo but posted here a while back. Have seen even scarier ones.
Once you've seen half a dozen cracked aluminum oil pump gears, you don't leave very many of them in engines that you care about....
Porsche superceded this gear to steel...and not because they were low on aluminum!
Are the new cam gears steel or just harder coated? I know Porsche changed the replacement oil pump gear to steel long ago, but every cam gear I've bought was coated aluminum. I was just using the oil pump gear photo as an example of what can happen if the coated aluminum gears are neglected. Of course, the oil pump gear was smaller and thus more likely to wear out over the same driving distance.
This is all good to know. And thanks to the PO of my '87 as he provided the cam gears and a steel oil pump gear.
This was the first cam gear I've ever seen that showed no wear. Makes me think twice about not buying new Porsche cam gears.
I do wonder if my 35-40k cam gear results are duplicated in other cars. Greg?
Is the new cam gear steel or coated aluminum? I guess time flies if the new gear is 7 years old. I didn't think the new version came out that long ago and I didn't know they are steel.
When I did my 16v engine this year I stayed with the square tooth belt so I could use early all steel gears, and I upgraded to the Porken tensioner. I painted them except for the belt running track to keep them looking nice so they wouldn't rust elsewhere. I cut up the old belt and wrapped it around the gears to mask the running track.
The steel gears last a really long time - much longer than the coated aluminum gears, as once the hardened coating on those wears through, they wear very quickly.
The Porken tensioner is a great and simple design.
Is the new cam gear steel or coated aluminum? I guess time flies if the new gear is 7 years old. I didn't think the new version came out that long ago and I didn't know they are steel.
Bill, the new (-04) cam gears became available in early 2011. Time does fly!! They are aluminum but look machined rather than cast, and have a hard coating of some sort. The reference to steel above was for oil-pump gears, where aluminum didn't work out so well.
The 35k - 40k mile gears without wear that are the subject of this thread are exactly what I would expect to see, virtually no wear and ready for another 60-100 thousand miles.
I have 155k on my original gears in the 90 GT Outlaw and they have finally worn through the coating (the car has had at least four well documented, complete timing belt changes with rollers tensioners and pump in its life). The next time I do a belt change all of the gears will need to be replaced in addition to the rollers, pump and tensioner.
I'm satisfied with Dave C's criteria to perform a complete system refresh at ten years as I'll never again drive the car regularly enough to get near the mile requirement.
As Dave, Greg and Sean state so well, the issue is not the belt, it is the ancillaries that are likely to take the belt out. Anything beyond that is "Belt Roulette".
Regards
Not to hijack this thread... I am considering a major enhancement to the 90 Outlaw GT motor and drivetrain and am thinking of a GB stroker with his fantastic new clutch now that things have evolved to such a reliable build. I guess my debate should include if I use the original GT engine or start with a donor... My problem it the fact that the original GT engine runs great and has been superbly maintained from new... It is tough to know when I should do it.
The 35k - 40k mile gears without wear that are the subject of this thread are exactly what I would expect to see, virtually no wear and ready for another 60-100 thousand miles.
I have 155k on my original gears in the 90 GT Outlaw and they have finally worn through the coating (the car has had at least four well documented, complete timing belt changes with rollers tensioners and pump in its life). The next time I do a belt change all of the gears will need to be replaced in addition to the rollers, pump and tensioner.
I'm satisfied with Dave C's criteria to perform a complete system refresh at ten years as I'll never again drive the car regularly enough to get near the mile requirement.
As Dave, Greg and Sean state so well, the issue is not the belt, it is the ancillaries that are likely to take the belt out. Anything beyond that is "Belt Roulette".
Regards
Not to hijack this thread... I am considering a major enhancement to the 90 Outlaw GT motor and drivetrain and am thinking of a GB stroker with his fantastic new clutch now that things have evolved to such a reliable build. I guess my debate should include if I use the original GT engine or start with a donor... My problem it the fact that the original GT engine runs great and has been superbly maintained from new... It is tough to know when I should do it.
85 to 95 32v Cam gears were changed by Porsche back in 2011 (thanks Jim), The 04 uses a much harder alloy with a hard anodized surface. Theory is no wear unless the belt is over-tightened.
83 to 86 16v had the same material change when Porsche up issued to -14
__________________
Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission? George Layton March 2014
928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
OK, I see the reason for my confusion about durability of the cam gears. I actually have not dealt with the 2011 updated harder aluminum gears yet. The original issue gears were not all that durable in my experience. So, my comments refer to gears bought prior to 2011. I'm still running older gears as I had a accumulated a bunch somehow in the 40 or so timing belt jobs I have personally done over the years on 928s. I've seen a lot of well worn pre-2011 gears in that time.
So, it is confirmed that the new gears are still aluminum but are considerably more resistant to wear. Whether the Porken tensioner reduces wear is still an open question. Had this been a pre-2011 gear with 35-40k miles I would have been impressed. The pre-2011 gears would not wear out in that time but they would show SOME, perhaps slight, wear.
12-23-2019, 10:18 PM
George Layton March 2014