Mike Simard

Yes, they do seem to have what appears to be a hard anodic type coating, it seems to be only applied to the outer area only somehow. It may not be practicle to have a coating more durable than the factory one although it may be possible in that the factory one is cast and a new one should be a better base metal for the coating, I don't know. Hard anodising could be very deep at several thousanths of an inch but once that wears the gear would be vulnerable. There are more durable coatings I've used in aerospace applications with very good hardness and slipperiness(word?) but they are microns thin. I may be seeing a worse case scenario in my engine, it has all the hallmarks of having been handled by monkeys, valve covers painted in car, random selections of sealants caked on gasket surfaces, mis-matched bolts with stacked washers when too long etc.

Shark Attack, you speak words of wisdom! Yes, we could all buy only Porsche authorized windshield washer etc and save alot of time on such wasted efforts as discussing materials design and how we can improve our pride and joy. We could also all drive Model T's because WHY would you take a chance driving anything else when the Model T has worked so well for so many years. They have many years of experience with the stovebolts used in a Model T, WHY would you try to engineer something better?

Macreel, a 9mm pitch is odd, are you sure about that measurement? It looks like Porsche used 3/8" or 9.525mm based on the gear measurement. The measurent of a timing pulley's supposed OD would be a belt thin section thickness less than the pitch circle. If a theoretical pulley has 48 teeth at .375 pitch, that's .375 x 48 / pi = 5.729 pitch circle. Since the belt flexes on the center of the thin section, the pulley would be that much smaller in diameter. Mine measures 5.67 which sure does sound like a 3/8" pitch pulley. I just found that interesting because of the non-metricness of it and hence this whole thread.

Thank you everyone for chiming in, this place is great!

GlenL

No HP loss, just heavier.

I'm curious because steel gives more coating options.

killav

I think that the heavier pulleys (read more inertia) would cause the belt to wear out much faster. It might not cost much horsepower, but the pulleys speeding up and slowing down would act like a heavy spring on the cam belt, causing premature stretching.

Imo000

Most 928s will have the cam gears changed only once in their life (assuming the replacements are new and not used). So if you replace them with new Porsche gears it will last another +100K. I have nothing against making new parts but have a feeling that they will end up costing X5 more than the original and their benefit over the OEM will be insignificant.

I’m pretty sure if the OEM engine mounts were less expensive than the Ford units, everyone would be using them. Since they are several times more expensive than the Ford replacements, most people are willing to use them as an alternative.

SharkSkin

Glen, any heavier rotating mass in the engine will reduce HP at the crank. The question is, how much? Would the difference even be measurable?

The oil pump sprocket was superseded by a steel part. The crank sprockets seem to last a long time, uncoated steel -- that was my thinking, if you're going to make new ones why not use a harder material in the first place? Mike makes a good point about belt wear, but how much difference would it make, really? You wouldn't want to duplicate the aluminum unit exactly, you'd want to take the stronger material into account and remove excess weight where you can. Or, if you want to get really fancy, make up an outer ring of steel teeth, machine the teeth off the aluminum, and press the steel teeth onto the aluminum hub.

Jim bailey - 928 International

If you want to improve the cam drive system perhaps look at the hub part # 928 105 459 00 the part that the gear bolts to. That is something which does break and then often breaks the camshaft and scrambles the valves. The cam gears can wear down until the high parts are worn off and you see through the gear without jumping time doing any damage and as noted often have 100,000 miles or more without being changed. The gears wear over thousands of miles and can be easily observed by simply pulling the car rotor and cover while also checking the t-belt tension which is something which should be done on a regular basis anyway if you are concerned about the health of the cam drive system and wish to avoid a valve incident . Generally speaking if you wish to improve something it helps to start out with something with a serious defect or very expensive other wise any benefit is nominal.

Mike Simard

Jim, do you mean this? I noticed that it looked like a fragile part because the key slot is not centered below the thick area but off enough to create a big weak spot. Are they all like that or ar some just positioned differently on the part? The 3 mounting holes are also not centered. Is that keyway the problem area?

Jim bailey - 928 International

Yes ,that is perhaps the weakest link....

SteveG

Jim said "valve incident" I love it. Somehow that evokes the ER doc saying to the family, "Mr. Mitchell has had a cardiac episode." or
The belt light comes on and I have a cardiac event.

SharkSkin

The holes are offset so the assembly only goes together one way. The keyway being skewed away from the meaty portion of the spider appears to be just one of those things... Porsche must have decided it was good enough, though it's easy to see in hindsight how it could have been stronger.

Jim bailey - 928 International

The engineer who designed that hub no doubt thought it was OK for the task unfortunately with 15-20 years of real world "testing" we KNOW it sometimes fails what we do not know is why but at this point knowing it is has a potential for failure is ALL that is needed. New hub is $26. part # 928 105 459 00 used 85-95 4 valve engines two per car .

Mike Simard

Dave, the keyway needs to be skewed in relation to the holes but the holes themselves should be centered, they have no reason to be skewed because the pulley that mounts there is a large flat area with nothing to clear. If the features in the picture were all skewed in the opposite direction the key would have been closer to the center of the mass and the part would be much stronger. I wonder if the features were to be skewed but a mistake was made and they're skewed the opposite direction?

Jim, if I were to make some hubs of a material and design that wouldn't break, would you trade some new timing pulleys for some hubs?

H2

Say....has anyone changed the cam gears (from old to new) WITHOUT the cams flipping and losing their timing setting? Or do you have to go through the whole mess of pulling the cam tower cover, using a caliper on a spindly arm, etc., etc?

Harvey

Jim bailey - 928 International

Mike I am quite sure you could make a much better hub but from a liability stand point even if I sold them for $50 each and made $30 or so "profit" if one should happen to appear to fail an upset customer might think we owe him/her $7,000 for a cam replacement-valve job so the first 230 hubs I sell might just cover the cost of one potential claim. When you are the biggest parts supplier with the deepest pockets there is some comfort in selling stock parts from proven suppliers. I know we are boring ..no blowers, no turbos just all the original stuff, usually in stock, to make a 928 run as it was designed to run !

Jim bailey - 928 International

Harv as old as these cars are now and so many people have worked on them I am not sure that we can assume that the cam gears/ cams are properly timed. I watched a guy doing a VW timing belt he just marked the crank and cam gears popped off the belt put on a new one with the paint marks lined up. I asked if the cam timing was correct ? He said well it drove in that way it should drive out just the same......and that was ALL HE CARED about ! Using the dial indicators to check and set cam timing is the right way just not the quick and easy way.