jcorenman

Yes, but it doesn't explain why Carl's profile is different.

Going back to Mike's comment, my only agenda here is decent engineering-- it's what I do, and have done for a long time. It all starts with an idea, then a design (drawings, cad files, whatever), then some prototype or test parts, then some inspection and testing, then some revisions if needed (usually are, in my case), and finally production. Doesn't matter if it is software or hardware, mechanical or electronical, the basic steps are the same.

So when I saw the post I thought "cool, another spin-off from Carl's Bonneville adventures". Except they don't match the factory's profile. They may be crappy internet pictures but the pixels that are there, are in the right place. That might be OK if there were some other well-tested profile that worked better, but that's not the case apparently. And these were offered for sale first, with testing to follow.

Carl, I am not meaning this unkindly at all, I have a lot of respect for what you have accomplished. But I think you are short-circuiting the design process, and that is not good. Cam sprockets are critical parts, if we lose a few teeth off these belts then it is not going to be pretty.

And frankly, with the factory sprockets at $300-400 there's not a lot of room to play. As much as we need independent vendors to stay interested in these cars, we also need the factory to stay interested. The reality is that limited-run parts cost a lot, whether you build them or Porsche does. The fact that there are less than 50 in the system says something about the volume they are seeing, also.

BTW, Sonnen Porsche's $300 price is not a total outlier, Sunset quoted me $323 today.

Cheers,

namasgt

If you look at the way the timing belt wraps around the cam gears with proper tension while the engine is on an engine stand, you will have a better understanding of why the tooth profile on the gear is important. With the engine in the car, it’s hard to see what is really going on.
In some sections of the system the belts tooth will not be in perfect contact with the cavity of the cam gear tooth, like the pictures Brenden has posted of the actual belt wrapped around the factory gear. The tooth will not be perfectly centered.
One good example is the passenger side cam gear close to the belt tensioner area. The belt tooth on this section would actually be pushed against one side, marked yellow on the below picture, and will leave a gap on the other side marked green. So one side of the belt tooth will be in full contact on the yellow side of the cam gear, leaving a large gap on the green side. Obviously if the profile of the cam gear tooth does not match perfectly to the profile of tooth on the belt, like the new after market gear, the tooth on belt will bend to one side showed by the black arrow; this could cause extra stress to the base of the tooth marked with a blue dot on the second pic. This stress could result in a short life of the belt and possibly separation of the tooth from the belt structure. If anyone has an S4 engine outside on the engine stand and can take detailed photo of how the belt is wrapped around the passenger cam gear from the tensioner all the way to the water pump, it would help in better understanding of what I said above. This is my experience looking at the installed belt on an engine outside the car.

heinrich

I think you're forgetting that the rear of this same belt with no teeth at all, pulls the water pump just fine. There is a lot of friction between the belt and the gears, and the only real function of these peaks and valleys, is to ensure that the belt and gears always stay in the exact same position.

Lizard928

Remove the teeth, set everything where it should be and rotate the engine by hand. I will bet anything you want that it will NOT be able to hold it.
If you think that the forces on the waterpump sprocket from the impeller are even CLOSE to equal those of the cam compressing the valve springs to open the valve, well, I guess that explains the GTS......

You are right, the wear is on the top of the gear. But this is caused by the belt slipping VERY SLIGHTLY as the tooth takes up the load.
If you increase the distance that the belt can move it will RAPIDLY accelerate the wear on both the belt and the gear.

However namasgt, does clearly understand what I am saying, and why this is a bad idea. The accelerated wear on the cam gears and belts is not what is dangerous, it is the von mises stress point that will be exaggerated on the tooth that will quickly cause the teeth to simply shear off.

4drgl

What a pissing match... I read the entire thing... got a headache hearing the same thing over and over... but...



Carl, thx for your efforts to bring a new product to the market.

I have a really stupid question... but would your new sprokets fit a 16v engine???

If they do fit.... couldn't one test them out on a 16v motor (since there's no chance of valve damage) and report back their findings? Or does the reduced compression, reduce the strain on the belt/ tooth wear?? Just curious.

Just an idea, and I'm just curious and learning, about all the problems with the bigger/better motors...

EspritS4s

So, what's to keep someone from offering a new gear set and belt that use a standard profile? The cam gears aren't the only ones that wear. I'm assuming the financials still aren't compelling even if the cam gears can be sold for $200 or less each?

Speedtoys

I cant see how swapping everything out, is cheaper than these gears..

daveo90s4

The cam [correction - I meant balance shaft belt] belt on my 1989 8 valve 944 has teeth on both sides; the same number of teeth on each side and careful visual inspection shows them to be of exactly the same profile. But not so, the belt teeth will only wrap around and mesh with the cam [balance] teeth properly with the belt turned one way in, not with it turned the other way in. The wrong way around and the belt teeth started to disintegrate (lots of belt dust, damaged belt teeth, jumped a tooth on one balance shaft) within just a few miles.

This suggests to me that in some cases (maybe not all) even imperceptible differences in belt / teeth profile interface can have significant adverse impacts.

Lizard928

I have never seen a 944 cam belt with teeth on both sides.
Their balance shaft belts do, but not the cam belt.

daveo90s4

Colin - yes thanks for the correction - see my edited correction above. But the point I was trying to make remains: in my case imperceptible differences in belt / pulley interface had a significant adverse impact on the performance of the system. Just saying.

Carl Fausett

From Jim Corenman

I agree completely. No attempt was made to short-circuit the proper process at all. Thats why we purchased the new sprocket and sent it off to be laser profiled, so we would get back a direct digital file of every profile of the gear. Accuracy beyond .001 as you know.

I just feel all this photo shop assessment of low-resolution internet mages of belts around the tooth (without tension) is a waste of time. But the guys are going to do what they are going to do.

It was an edgy proposition to make this part - I admit knowing that when I got in. Normally I would wait until a part becomes NLA before I give it a second look.

But last year I started having trouble locating good sprockets for my engine rebuild customers. So that drove me to do this if only so I would have a steady and reliable stream of parts to continue my engine rebuilds.

Carl Fausett

Has any of the engineers here mentioned there is a reason that there isn't full contact of the tooth to the sprocket in the position being examined (Perpendicular, or 90 degrees of entry) ?

There isn't supposed to be. That space is provided for entry and exit of the belt tooth into the groove during rotation.

If you want to do it right, in addition to the examination at perpendicular, do another examination at 30 deg entry, 45 deg entry, 60 deg entry, 75 deg entry and you'd have e reasonable set of images that you need. The only photos I've seen here show 90 deg entry (perpendicular).

Lizard928

Carl,

Could you please provide a high resolution image of a gates or Porsche belt with the teeth engaged like Rogers and BC have done so that we can get a good idea as to how it fits.

Carl Fausett

Asked and answered. Post #33

jcorenman

The problem is that I am not qualified to make an analysis of whether a particular sprocket profile is compatible with a particular belt. That is a highly specialized area of engineering, and I doubt if anyone outside of Gates (or one of the other major players) is truly qualified to pass judgement on sprocket profiles.

My criteria for aftermarket parts is much simpler: Is the proposed replacement identical in every way?

If not, then we have to get into long discussions about what means "better" in some aspect. In this case, and particularly with respect to the profile, I would respectfully suggest that none of us are qualified to do that.

Carl, from your earlier comments I understand that it was your intention that the profile match exactly, by carefully measuring a new sprocket and then duplicating the profile. The lousy internet pictures suggest that something came out different, when the parts were finished. If that is the case, then something went astray either with the measuring process, or with machining. Alternately, some hi-res macro shots will answer the question. Optical comparisons are done all the time, for QC.

Cheers,