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Kevlar timing belt tensioning question

Old 01-08-2019, 09:39 PM
  #1  
odonnell
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Default Kevlar timing belt tensioning question

I know timing belt threads are not a crowd favorite, but I have a question I couldn't find an answer to after searching.

The Kevlar belt does not stretch in the same matter as rubber, it's significantly less elastic. Therefore I am not sure if the factory specifications are equivalent (setting tension via deflection). Obviously I am not the first one to use this belt so maybe it's fine. But perhaps there are more factors to keep in mind, or just general advice from those who have used these belts for a while and wouldn't mind sharing. I have an Arnnworx timing belt tool kit.

Before any non-value comments about the belt choice, I snagged this belt for a price that made the usual price premium a moot point. And I understand the interval is not longer, this is far from my first belt job, I just like the idea of it being more robust.
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Old 01-08-2019, 11:14 PM
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noahscott
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there is a kevlar timing belt?!!!! Why have I not heard of this till now?
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Old 01-08-2019, 11:17 PM
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odonnell
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Look up Gates part number T107RB. It's not a silver bullet, but it is a stronger material. The normal interval should still be followed. A lot of guys who race these 944s seem to use them. I'm sure it's overkill but it's not that much more expensive if you shop around.
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Old 01-08-2019, 11:38 PM
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3 months into the ownership journey and this is the first ray of hope I have seen. Every time I see a post re timing belts I feel I should be changing them every 32 miles.. Mine we done about 800 miles and two years ago along with the water pump.... I fear when I get it out of winter storage the belt will spontaneously combust.
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Old 01-08-2019, 11:45 PM
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They're not that bad. If the maintenance is followed, there is no reason to worry about it. I've done timing belts on other cars and the 944 is by far the easiest. It's blown out of proportion.
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Old 01-09-2019, 12:50 AM
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Does gates have 944 specific instructions for this belt?

if not the stock specs should be close enough. Its still a rubber belt but with kevlar fiber instead of...nylon? Glass? Whatever regular belts are made with. And the pulley bearings are made for stock ish tension too.

Good excuse to check tension every year or so though.
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Old 01-09-2019, 06:52 PM
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Swenny
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My non-value comment would be that this timing belt/balance shaft belt set up is total bull. This car should have been a straight six, non interference with a chain driving the overhead cam. Side draft carbs optional. The Japanese pulled it off with the 240Z. End of non value comment.
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Old 01-09-2019, 09:14 PM
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I have used the Gates Kevlar Timing belt for the last 10 years on my 951 track car and have been very happy with how they have performed. I would change the Kevlar timing belt every 3.5 years as routine maintenance and just tension it to factory specs. Honestly the Kevlar belt still looked brand new when I would do the swap. It's well worth the $75 for the belt.
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Old 01-09-2019, 10:00 PM
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odonnell
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Thanks! That's the feedback I was looking for. During tensioning, do you recall there being any differences as far as how it feels? For example, some people do the "twist" method, I do it as a sanity check after setting it using the tool.
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Old 01-09-2019, 10:34 PM
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I never did the twist test. Just set it with the timing belt tension tool.
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Old 01-10-2019, 06:13 AM
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tempest411
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Originally Posted by Swenny View Post
My non-value comment would be that this timing belt/balance shaft belt set up is total bull. This car should have been a straight six, non interference with a chain driving the overhead cam. Side draft carbs optional. The Japanese pulled it off with the 240Z. End of non value comment.
A chain you say? To heck with that! Chains stretch. The camshaft should be driven with gears! Seriously...
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Old 01-10-2019, 10:01 AM
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MAGK944
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Originally Posted by odonnell View Post
...I just like the idea of it being more robust.
<NoneValueStatement>

Was the problem with the belts ever to do with them not being robust enough?

</NoneValueStatement>

<ValueStatement>

One was fitted to a car I recently purchased, no history but the date code was only two years old so I just checked it with the Arnworx tool and it didnĺt need adjusting

</ValueStatement>
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Old 01-10-2019, 11:04 AM
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tempest411
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Originally Posted by MAGK944 View Post


<NoneValueStatement>

Was the problem with the belts ever to do with them not being robust enough?

</NoneValueStatement>

<ValueStatement>

One was fitted to a car I recently purchased, no history but the date code was only two years old so I just checked it with the Arnworx tool and it didnĺt need adjusting

</ValueStatement>
How many stories do you hear about chains snapping and trashing the engine? Of the three principle ways to drive a camshaft, belts are the least robust. Ideally the cam-drive mechanism should last as long as the rest of the engine. Chain drives that make use of guides and tensioners have their problems, but even they last longer than the interval for belts. Only gear dives are truly problem free.
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Old 01-10-2019, 11:31 AM
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MAGK944
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Originally Posted by tempest411 View Post
How many stories do you hear about chains snapping and trashing the engine? Of the three principle ways to drive a camshaft, belts are the least robust. Ideally the cam-drive mechanism should last as long as the rest of the engine. Chain drives that make use of guides and tensioners have their problems, but even they last longer than the interval for belts. Only gear dives are truly problem free.
Agreed, my point was, has the problem been that the belts were not up to the job or something else? If the belt has been changed on schedule and tightened correctly, I suspect failures occur because of bad water pump or roller bearings or some other occurrence like a balance belt taking out the cam belt. Did anyone have a belt actually fail because it was not ôrobustö enough to do the job and making it out of Kevlar would have prevented the failure?
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Old 01-10-2019, 12:02 PM
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bw993
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The stock timing belt is probably very adequate for most 944 cars. The reason I went with the Kevlar belt was because my track car was tuned for E85 and ran 21 lbs of boost, so rwhp and torque were much higher than stock. Also, the stock timing belt was based on a 70's synthetic rubber compound that I understand was susceptible to breakdown if it got exposed too much oil/ethanol/gasoline. My only other observation is that when I have removed stock timing belts from cars there were signs of fatigue and wear with the stock belt, which I have never seen when replacing a Kevlar belt.
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