Kevlar Reinforced Timing Belt???
04-20-2002, 03:09 PM
#16
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[quote]Originally posted by jim968:
a few of the later models don't require re-tensioning of the timing belt<hr></blockquote>The 968 is the only model with a fully automatic dynamic timing belt tensioner. The '87 and on 944 have a spring tensioner for the timing belt, but it's not automatic. The spring is used to apply a preset tension to the belt during a manual procedure. [quote]AFAIK, _all_ (even the 968's) require retensioning of the balance shaft belt<hr></blockquote>The 968s are actually more critical with balance shaft belts for some reason. In 1995 Porsche released a Technical Service Bulletin that required a new 18mm wide belt for all 968s, but it was optional for the 944. If you purchase your parts from Porsche the 18mm wide belt is the only one available now, but I would not be surprised to see the old 15mm belt still in circulation from 3rd party manufacturers. The new belt gets a tension of 3.5 +/- 0.5.
a few of the later models don't require re-tensioning of the timing belt<hr></blockquote>The 968 is the only model with a fully automatic dynamic timing belt tensioner. The '87 and on 944 have a spring tensioner for the timing belt, but it's not automatic. The spring is used to apply a preset tension to the belt during a manual procedure. [quote]AFAIK, _all_ (even the 968's) require retensioning of the balance shaft belt<hr></blockquote>The 968s are actually more critical with balance shaft belts for some reason. In 1995 Porsche released a Technical Service Bulletin that required a new 18mm wide belt for all 968s, but it was optional for the 944. If you purchase your parts from Porsche the 18mm wide belt is the only one available now, but I would not be surprised to see the old 15mm belt still in circulation from 3rd party manufacturers. The new belt gets a tension of 3.5 +/- 0.5.
04-20-2002, 03:12 PM
#17
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Why do our cars require timing belts to be changed so often? My '94 Prelude that I had didn't require a timing belt change until 90K miles. My friend's 9.5K RPM Integra is going strong with over 60K on the original timing belt. It isn't showing ANY kind of wear, and it is suggested that the belt be replaced at 90K.
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04-20-2002, 05:36 PM
#18
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Just had my TB change - should I take it back in 1000 miles to be retensioned? I asked the mechanic about that and he said it has an automatic retensioner. This is true, but why do people take them back to get retensioned?
-Matt
-Matt
04-20-2002, 05:59 PM
#19
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"Why do our cars require timing belts to be changed so often?"
Probably something to do with the size of the belt and the loads it encounters. As Tom mentioned, Porsche went to an 18mm wide belt later. But it may still not be enough...
On my Supra, the belts were about 30mm wide and I changed them every 125k-miles without any problems.
Probably something to do with the size of the belt and the loads it encounters. As Tom mentioned, Porsche went to an 18mm wide belt later. But it may still not be enough...
On my Supra, the belts were about 30mm wide and I changed them every 125k-miles without any problems.
04-20-2002, 06:49 PM
#20
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Why so much belt maintenance? As Tom stated, the aluminum expansion issue. Also, it's a long belt... The same inches per inch of stretch leads to more slack. And (haven't actually quantified this 'un) I suspect that we're putting more power to the cam than some Honda or Pinto... bigger displacement means bigger valves means stiffer springs & higher inertial loading means more load on the belt.
(Long rambling soap-box rant follows; dull & boring warning!)
It's really not that big an issue, IMO. Do it once every 45K or so... that's maybe five times in the life of the car, probably twice per owner on average. Do the water pump & seals every other belt. Get it retensioned. Drive it, enjoy it.
If the costs or hassle bother y'all, frankly you need to either get a Toyota or learn to DIY it. These aren't exactly new cars any more; they were never low-maintenance cars even when new. They're gonna take some upkeep. This is the downside of getting Porsche pleasure (or 'status', for some) for a cheap entry price.
BTW, the performance of these cars _is_ excellent... certainly by the standards of 1982, when they were first marketed. True, the na didn't evolve much; that's what the Turbo, S, S2, and 968 were for. The handling of the na is _still_ first-rate. If y'all just want a cheap dragster, get a friggin' Mustang. If you want low operating costs, get an Echo....
Jim, what doesn't kill us makes us stronger... or closer to going postal....
(Long rambling soap-box rant follows; dull & boring warning!)
It's really not that big an issue, IMO. Do it once every 45K or so... that's maybe five times in the life of the car, probably twice per owner on average. Do the water pump & seals every other belt. Get it retensioned. Drive it, enjoy it.
If the costs or hassle bother y'all, frankly you need to either get a Toyota or learn to DIY it. These aren't exactly new cars any more; they were never low-maintenance cars even when new. They're gonna take some upkeep. This is the downside of getting Porsche pleasure (or 'status', for some) for a cheap entry price.
BTW, the performance of these cars _is_ excellent... certainly by the standards of 1982, when they were first marketed. True, the na didn't evolve much; that's what the Turbo, S, S2, and 968 were for. The handling of the na is _still_ first-rate. If y'all just want a cheap dragster, get a friggin' Mustang. If you want low operating costs, get an Echo....
Jim, what doesn't kill us makes us stronger... or closer to going postal....
04-20-2002, 08:05 PM
#22
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Well said, Jim. <img src="graemlins/r.gif" border="0" alt="[king]" />
Back to the original topic, I don't care what they use to reinforce the belt, it's still surrounded by the same rubber compound. It wears the same, it dries out the same, it just might not stretch as much. Just did mine at 38 months/8000 miles, and don't regret it.
Back to the original topic, I don't care what they use to reinforce the belt, it's still surrounded by the same rubber compound. It wears the same, it dries out the same, it just might not stretch as much. Just did mine at 38 months/8000 miles, and don't regret it.
04-21-2002, 03:53 PM
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[quote]Originally posted by Danno:
<strong>Yeah, sometimes the belts fail by having the teeth ripped off...</strong><hr></blockquote>A good friend of mine inspected the belts in his 30K mile 968 when it arrived from back East and he was horrified to find out the balance belt was missing a bunch of teeth... and the belts were supposedly just checked prior to the purchase.
<strong>Yeah, sometimes the belts fail by having the teeth ripped off...</strong><hr></blockquote>A good friend of mine inspected the belts in his 30K mile 968 when it arrived from back East and he was horrified to find out the balance belt was missing a bunch of teeth... and the belts were supposedly just checked prior to the purchase.
04-21-2002, 03:55 PM
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[quote]Originally posted by M. R. Olde:
Just had my TB change - should I take it back in 1000 miles to be retensioned?<hr></blockquote>No. Take it back in 2000-2500 miles per Porsche's instructions. [quote]I asked the mechanic about that and he said it has an automatic retensioner.<hr></blockquote>Get a new mechanic. This one doesn't know anything.
Just had my TB change - should I take it back in 1000 miles to be retensioned?<hr></blockquote>No. Take it back in 2000-2500 miles per Porsche's instructions. [quote]I asked the mechanic about that and he said it has an automatic retensioner.<hr></blockquote>Get a new mechanic. This one doesn't know anything.
04-21-2002, 04:03 PM
#26
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So what gives with the "tensioner" on the 87+ cars? I thought it was there to automatically tension the belt to what it needed to be, and to remove the need to re-tension and worry about the tension of the belt later? Is it just eye candy, or is it really serving a purpose?
04-21-2002, 06:47 PM
#28
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[quote]Originally posted by PrerYDoG:
<strong>So what gives with the "tensioner" on the 87+ cars?</strong><hr></blockquote>It's not an automatic tensioner in the sense that the tension in the belt is dynamically adjusted while the engine is running. It is only a manual aid in setting the tension.
Basically, there's a coil spring connected to the mechanism that holds the timing belt roller. You set the engine to TDC, lossen two nuts, push on the belt a few times to exercise the "tensioner" in and out, tighten the bolts... and the correct tension is not supposed to be in the belt. This has to be done manually after the 1st 2000-2500 miles and every 15K miles (or less) thereafter.
Any mechanic that says this is an "automatic" tensioner does not know what he is talking about and should be avoided.
<strong>So what gives with the "tensioner" on the 87+ cars?</strong><hr></blockquote>It's not an automatic tensioner in the sense that the tension in the belt is dynamically adjusted while the engine is running. It is only a manual aid in setting the tension.
Basically, there's a coil spring connected to the mechanism that holds the timing belt roller. You set the engine to TDC, lossen two nuts, push on the belt a few times to exercise the "tensioner" in and out, tighten the bolts... and the correct tension is not supposed to be in the belt. This has to be done manually after the 1st 2000-2500 miles and every 15K miles (or less) thereafter.
Any mechanic that says this is an "automatic" tensioner does not know what he is talking about and should be avoided.
04-21-2002, 08:02 PM
#29
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Even with the 'automatic' tensioner, you should re-check the tension afterwards with "THE GAUGE" as well to verify the settings. The spring in the tensionser can loose strength over the years, leading to varying tensions between different cars.
Even on the same car, the tension may be different depending upon the amount of stroke required to take up tension on the belt. I've heard of belt-tension readings afterwards from the 'gauge' as being all across the range.
The only effective way to make an truly automatic tensioner is with a hydraulic system.
Even on the same car, the tension may be different depending upon the amount of stroke required to take up tension on the belt. I've heard of belt-tension readings afterwards from the 'gauge' as being all across the range.
The only effective way to make an truly automatic tensioner is with a hydraulic system.
04-21-2002, 08:17 PM
#30
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[quote]Originally posted by Danno:
<strong>Even with the 'automatic' tensioner, you should re-check the tension afterwards with "THE GAUGE"</strong><hr></blockquote>I've always done that and it's always been about the same, 3.7 to 3.8.
<strong>Even with the 'automatic' tensioner, you should re-check the tension afterwards with "THE GAUGE"</strong><hr></blockquote>I've always done that and it's always been about the same, 3.7 to 3.8.