Gates Racing Kevlar timing belt

[Cruise98]

Crenellated?! Are you trying to expand our vocabulary?

The Lotus, 944 and 928 communities have similar reactions to all things timing belt related.

[gruhsy]

I’m surprised more people don’t just make a non interference setup.
Chris have you designed any non smacky pistons lately with Mahle? I recall you mentioning working with them recently.

After pulling apart a water pump….see pics I posted in a thread on here I feel those bearings are junk quality. Can definitely see those being a seizing item.
I am still trying to source a better option.
I have been bugging Engineering at work also to keep their eyes out for bearings that might work better. Not my highest project priority though right now.

[chris white]

In all my years (over 25) of playing with 944s I have never seen a well maintained 944 break a belt. Making a non interference piston is like admitting you might brake a belt due to bad maintenance (ok, that’s a little harsh) so I dont worry about it

[DMRK]

Thanks for all the input. I think I will just stick to the stock belts all things considered.

[gruhsy]

In all my years (over 25) of playing with 944s I have never seen a well maintained 944 break a belt. Making a non interference piston is like admitting you might brake a belt due to bad maintenance (ok, that’s a little harsh) so I dont worry about it

I have always looked at Interference engines as a way car companies can bend us over with maintenance costs. I hear you about proper maintenance of course. Easy for me when my driving season is so short. Typically sometime in October through end of April is project season.
So with 25 years of 944’s you made me realize I am past the 30 year mark owning 944 turbos . Got rid of my 67 Chevelle and bought my first turbo. You’ve built just a few more than me though .

[Tom]

By my math, I've had mine just about 25 years. I'd have to look it up, but bought mine in the summer of '98 I believe. It's a keeper. Because it's kind of a test mule for me, I bet I've never had more than 10k miles on a belt. Between actual repairs, and trying out some new idea/thing, I tend to replace the belt whenever it's off, which is pretty often.

[DMRK]

I agree with others that the Gates blue belt is not totally necessary, the standard ContiTech or equivalent belts can last well past the recommended replacement interval (though I obviously don't recommend pushing this!). Roller and water pump condition are paramount. I just acquired another 944, an S2 cabriolet (wasn't looking for one, but it was cheap, needs a clutch) with a 12-year old timing belt that looks great, only has a few thousand miles, but I will be replacing it along with the rollers (and the timing chain tensioner pad).

I have a Gates "racing" belt on our '74 Jensen-Healey roadster with the Lotus 907 engine, as it happens to be the one readily available via the Lotus parts supplier that is local to me. The tension requirements do seem to be different from a standard belt (blue belt is stiffer and requires less tension), which sends the Jensen-Healey crowd into a tizzy as they are already neurotic about timing belt tension specs and tools and the pros and cons of each. Some swear by one tensioning tool, some by another, others use acoustic tools to measure the frequency generated by plucking the belt like a guitar string (which some OEMs use). I have a lot of experience with 944 and 928 timing belt tension, so I simply chose tension by feel/twist, and backed it off by a hair to quell whine, has been great for 20K+ miles with no visible timing gear wear.

While we are on the subject of timing belt tension, our other strange car with a timing belt, a 1981 Alfa Romeo GTV6, has a very clever but somewhat Rube Goldberg mechanism to maintain belt tension, it is actually referred to as a DE-tensioner, kinda like the 928 version but more complicated. Check out the US patent for it here:

https://patents.google.com/patent/US4077272A/en

I had a Jensen-Healey some 30 years ago and the teeth on the timing belt let go. It wasn't that big of a deal on the 907 as it is not an interference engine. I am much better with maintenance intervals these days. I also like the GTV6 and almost bought one but ended up with a Lancia Scorpion and then a Zagato. Now days I stick to mostly P-cars as they seem to be more enjoyable to work on for me.

[Thom]

I have lost count of how many times I loosened and retightened the same timing belt on the previous engine when I was taking the cam housing off for various reasons (valve train noise, camshaft change) but that belt was on and off at least a good ten times and never broke, even tightened on the tensioner's spring without actually measuring the tension. These belts are just strong.

On another note, does someone with the factory Staeger tool know how much the correct tension measured with the tool translate in terms of frequency? Many manufacturers these days give a Hz rating for belt tension and several phone apps allow for measuring belt tension easily, like Gates Carbon Drive and Carltune.

[Tom]

I have lost count of how many times I loosened and retightened the same timing belt on the previous engine when I was taking the cam housing off for various reasons (valve train noise, camshaft change) but that belt was on and off at least a good ten times and never broke, even tightened on the tensioner's spring without actually measuring the tension. These belts are just strong.

On another note, does someone with the factory Staeger tool know how much the correct tension measured with the tool translates in terms of frequency? Many manufacturers these days give a Hz rating for belt tension and several phone apps allow for measuring belt tension easily, like Gates Carbon Drive and Carltune.

I don't, but want to come up with a spec using the engine I have on the stand. Just too many projects, one of which you'll be happy to know should be all done this weekend.

[cda951]

I had a Jensen-Healey some 30 years ago and the teeth on the timing belt let go. It wasn't that big of a deal on the 907 as it is not an interference engine. I am much better with maintenance intervals these days. I also like the GTV6 and almost bought one but ended up with a Lancia Scorpion and then a Zagato. Now days I stick to mostly P-cars as they seem to be more enjoyable to work on for me.

Sounds like you were lucky, my Jensen-Healey with higher-compression pistons most certainly is an interference engine!

I have always looked at Interference engines as a way car companies can bend us over with maintenance costs.

Not really, almost any engine since about the 1990s is an interference engine because modern, compact combustion chamber design dictates that if the engine loses time, the pistons and valves will be occupying the same space at the same time, no way around it. This is true for any DFI turbocharged engine as well (these usually have about 10:1 CR).

On another note, does someone with the factory Staeger tool know how much the correct tension measured with the tool translate in terms of frequency? Many manufacturers these days give a Hz rating for belt tension and several phone apps allow for measuring belt tension easily, like Gates Carbon Drive and Carltune.

I'll try to remember next time I do a 944 timing belt. My shop doesn't work on too many 944s anymore, but I did just acquire a nice 944S2 cabriolet from a customer for cheap (needed a clutch) that could use belts, I'll see if I can get the belt in the factory tension range for the tool with the spring-loaded tensioner and give it a twang.