Mike Simard

I just measured the timing belt pulleys on my 87 project engine, not to re-invent the wheel but possibly make new pulleys. I expected a 10mm pitch but the diameter of the pulleys and number of teeth imply a 3/8" pitch instead. Am I crazy? Could Porsche have specified an inch size belt?

macreel

Mike... mine is an HTD belt and has 9 mm pitch.
[3/8 is about 9.5 mm]

The face width of the cam gear is ~ 31 mm.


G'luck.

Garth S

3/8" pitch it appears to be .... and the TB is spec'd at 58219 X 1" width, and printed as such on the backside

GlenL

Did you measure to the outside of the sprocket teeth? Or the base cricle?

Jim bailey - 928 International

When you can BUY new cam gears which we KNOW work for like $112 each WHY would you want to guess at the proper material and go to all the effort of making them finishing the surface then proving over many years of driving that they worked.... I guess I could plow a field plant wheat grow a crop grind the grain and make bread but WHY ?

lorenolson888

I think they are actually a standardized metric HTD design

I agree with Jim if your intent is to make an identicle gear.

But if you make one that makes cam timing adjustments easier and tooless then maybe I this would be worth it...

LO

GlenL

Are the pulleys aluminum? Or what?

Mike Simard

I've considered making gears in order to have a more durable coating, probably hard anodising. The gears I have are badly worn and I wonder about the duability of future ones but it's not a high priority when they can be bought. Do you know what kind of surface treatment the Porsche ones have? FYI, if I did get really bored and make some it would be by buying a length of extruded gear stock and the cutting lengths, finish machining holes etc and having them hard anodised or possibly other coatings I've used in odd applications. Common pitches and tooth counts are available in bar form. The reason for my post was that I found it odd that Porsche would have used an inch (or 9.5mm) size, were they trying to be able to use an already manufatured belt when they designed the engine? Just curious.

Glen, the gears are aluminum except for the crank gear which is steel. For measuring, multiplying the pitch by number of teeth gives you a circumference which the diameter can be deduced from, the difference between 3/8" and 10mm is significant in overall diameter, much more than differences of peak and root of the groove.

Mike Simard

Mac', is that an early square tooth belt?

Shark Attack

see my signature, that should answer all your questions. why did we fly to the moon? we sure didnt bring back anything of value... it was what we learned getting there and back that was the value of the project. Nasa could have bought a harly and painted it white,,, but no they had one built by OCC....

macreel

Mike... nope. HTD came after early square tooth version.

Bill Ball

The factory coating is hard anodic. Maybe you can find harder. I've seen gears at 90K miles that looked new and others that didn't last 40k miles. An important variable should be the tension setting, but the short-life pair I saw were not knowingly overtensioned. However, a dry tensioner could have contributed to overtensioning once the engine warmed up in that case.

danglerb

Have you tried bread? Its really good.

danglerb

The moon rocks were so valuable that basically nobody got any. Instead NASA studied them and made fake ones to give everybody else.

SharkSkin

I wonder how much HP would be lost if they were made of steel instead of aluminum. Maybe 1 hp tops?