[SILVY968]

I have my belys done at less than the reccomended intervals, and by my PM.

Last week the engine started to run rough, almost like I was on a rough piece of road. The rough feeling stopped when the clutch was pushed in...enfine problem not running gear or road.

Called my PM who thought it was the belt to the crank counterbalance shaft.

It was changed with the cam belts and tensioned after 2K miles.

My PM tells me that the counterbalance belt is a manual tension adjust and should be done yearly.

My belt snapped and was replaced for under $400 after all is said and done.

My PM uses only Porsche belts.

If the belt would have tangled with the cam belt when it went, the resultant damage would have been in the thousands.

Check yours or adjust if it has been more than a year since your cam belt replacement.

Brian

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[tamathumper]

Whoa! Glad you caught it.

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[JWahlsten]

When did you last do the belt change? Do you know what brand went in? Glad it worked out to be only the balance shaft for you...

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[flash]

correct - that belt should be adjusted every year.

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[Cloud9...68]

I just wish there was an adjustment procedure that made sense... <img src="/forum/images/smilies/968/sad.png" class="smilie" alt="" />

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[ds968]

[quote name='flash' timestamp='1343082782' post='129847']correct - that belt should be adjusted every year.[/quote]



That one ( the balance belt adjustment ) is much more of a mileage issue than it is a timeline issue - it's fairly loose to start with, and after the first 2k miles tension adjustment it does not get much more loose simply with time, only with mileage... as in 10k or 15k miles, so yes, one year if the car is a daily driver, but if you put 2k or 3k miles a year on it, the four year interval when you change the timing belt should be ok.

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[flash]

not exactly true. rubber ages regardless of mileage. there is a whole science about polymer cross-linking and how it affects rubber.



how quickly it goes out of adjustment really depends on heat cycles, and the composition of the belt. as an example, a conti belt will stretch pretty quickly.

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[SILVY968]

Joe,



New Porsche OEM belts were installed 20,000 miles ago, then adjusted 2K latter = 18,000 miles ago.

Belts installed 1 year and 3 months ago, adjusted 2 months later = failed 1 year and 1 month after installation.

Not much room for error. I had hoped that Porsche OEM belts could go longer than that!

Makes me worried about quality going downhill, even at Porsche, and the state of the cam belt!

They checked them and the appear OK, they said the belt snapped clean.

Brian

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[ds968]

Is there no legal recourse against Porsche ( for the engine damage ) given the ridiculously premature failure of a belt at only 1 year and 20 k, when their manual suggests belt change only at 60k miles intervals ?! Also the manual does not even mention how many years , just the mileage. They do recommend balance belt inspection annually, after the initial 2k re-tension, but that's irrelevant here ; we're talking about selling an OE belt with an implied lifetime of 60 k miles, assuming all the prescribed tension and inspection intervals are observed...which Brian has clearly done , and yet the belt fails at a third of the expected life ! Any attorneys care to chime in re Porsche's liability for engine damage in a case like this ? And it probably makes a difference if the dealer installs it vs. an independent, because in case of the latter they can assert that " improper installation " led to the problem.

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[flash]

the common myth is that an "OEM" belt is any better than any other belt. all "OEM" means is that the part meets the fitment and application minimum specifications. it does not mean that it is better than any other part, and in fact often means it is of less quality, due to the fact that the manufacturer needs to maintain a profit margin that is often higher than other retailers. in order to be competitive, they have to buy cheap. that opens the door for lower quality parts.

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[ds968]

[quote name='flash' timestamp='1343095216' post='129870'] there is a whole science about polymer cross-linking and how it affects rubber.

.[/quote]



I kinda disagree, and think that particular science is more hype than fact. I currently have 4 cars , two of which have 150k miles on them and the other two have over 100k miles. Except for my timing belt incident, and the clutch hose , not a single other rubber component has ever failed to date, in any of the cars , in decades of ownership and hundreds of thousand of miles. I have not replaced anything ( like radiator hoses, vacuum lines, etc ) ma of rubber since the cars were purchased off the lot. Same for the 250k mile 944 for 18 years of ownership , all original rubber hoses, etc and not one failure. So you can understand why I don't believe in the theory ..sure, eventually rubber will lose some its flexible characteristics, but a lot of rubber , depending on its fabrication and what goes into it can last practically a lifetime.

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[flash]

you cannot apply what happens on one car to what happens on this one. that is a part of the science. this system was designed for an engine that was 20% smaller, with a power output of 60%. the stresses on this engine are far greater than on a 944. the easiest thing to point this out is the torque of the engine. every "pull" of every revolution of the engine tugs on that belt with a force that is nearly double that of the 944. each revolution thereby yanks on that belt harder, increasing the wear and tear.



the science is not hype. it's very real and measurable. just because you ran something for a longer period and did not have a failure does not mean that the parts were not degraded. it only means that you were lucky. you are now painfully aware of the results of your luck running out. i would think that you would apply that experience and open up to the idea that maybe those who have tested these things are right.

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[tamathumper]

On the other side of the spectrum, my Chinese tractor (Jinma) has air and radiator hoses that have cracked wide open after only three years <img src="/forum/images/smilies/968/whine.gif" class="smilie" alt="" /> <img src="/forum/images/smilies/968/glare.gif" class="smilie" alt="" />

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[flash]

yup. it happens. i've had stuff go like that. it all depends on how close to the stress limits the components are while in service, and then how much heat is applied, how often, and over what span. a belt that sits can be worse off than a belt that is in regular use.



i recently found a bag of unopened and unused rubber bands in a drawer. each and every one of them broke when i tried to use them.

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[tamathumper]

Shockingly, the tractor only has 85 hours on it over that span of 3 years, and sits indoors the rest of the time (ruling out exposure to sun and elements other than temperature swings). It's just really, really bad Chinese rubber and plastic.

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[Langley968]

[quote name='tamathumper' timestamp='1343145026' post='129895']

Shockingly, the tractor only has 85 hours on it over that span of 3 years, and sits indoors the rest of the time (ruling out exposure to sun and elements other than temperature swings). It's just really, really bad Chinese rubber and plastic.

[/quote]



Shame on you for buying "Made in China" instead of "Made in the USA"! <img src="/forum/images/smilies/968/icon_lol1.gif" class="smilie" alt="" />

Wait! Do the Americans even make a "small" tractor? Hum...



My wise father always told me: "You get what you pay for" (at least MOST of the time!)

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[flash]

ironically, gates, the original provider for the belt, is generally less expensive than some of the competing belts. it is currently, and once again, the OEM belt, though it has not always been. it has changed over the years, dependent on the agreement porsche could make with a given manufacturer.



but generally yes, you get what you pay for. my point was that just because it's OEM it is not necessarily any better than anything else, and often worse.

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[ds968]

well, it's not just luck or the difference with one car vs another, it's the case in ALL the cars I have ever owned, so that's a bit too much to be just a fortunate coincidence, if you ask me..



as for the timing belt, you know that it's been subjected to extreme conditions under which it was not designed to function ; most normal people don't typically drive their cars the way I do , so six years + of being driven almost never below 4,000 rpm ( even when cruising ) and then after all that time and the unusual level of stress placed on it coupled with a temperature swing from 100 F to < 40 F back to 100 F+ , at that age and mileage anything would have stretched and then snapped... so we can't use that as an example of rubber longevity. besides, on top of it all that belt could have been a Conti, no idea what the <acronym title='previous owner'>PO</acronym> had in there ( I now have Gates )



the OE clutch hose is just an idiotic design waiting to break, who the heck combines rubber with metal at a joint in a high pressure hose and expects that to last ? thankfully now I also have the DR1 stainless steel one



more on rubber durability - can't use rubber bands as an illustration, they're not engineered and fabricated as auto parts are

all rubber is not the same ; I have rubber watch bands that are now over 15 years old and they are as soft and as flexible as they were when brand new.



you may also be surprised to hear that car tires' SHELF life could be 50 years, and in some cases could last as much as 75 years without compromise in their function and safety - this comes from a very credible sr. manufacturing engineer and close friend of mine ( while I lived in Ohio ) and who was able to reveal this only after he retired from the tire mfg for which he worked ( the company shall remain nameless to protect the innocent, but you can put two and two together, lol )



just sayin ' ..

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[flash]

i think you're missing the point. the 968 is NOT the 944. it uses some of the same parts, but puts a LOT more load on them. therefore, they will wear out faster. you are pulling on that belt almost twice as hard on the 968 as on the 944. it shouldn't be too hard to imagine what happens when you do that.



regarding extreme conditions, high rpms are not extreme conditions when it comes to belts. sure, there is more friction, but it is not as bad as sitting idle. letting a belt sit for extended periods is much harder on it than revving the piss out of it. the best thing you can do for a belt is to run it regularly. that helps keep it from hardening as fast. take a belt off of an engine that has sat, and one off on one that has been running. the one that has sat will retain the pulley shape. the one that has been running will be more of a circle.



it's just not as simple as mileage. around town miles are harder than freeway miles. track miles are harder than around town miles. time between drives is a factor too. my belts sit for months. then i go out and flog them. that has proven to be a problem.



as for the the other cars, they are designed with new parts specifically fit to that engine. they aren't engines that have been beefed up to almost twice the power, but still kept the same wear parts. you cannot compare other engines to the 968. it is a poorly designed belt drive comprised of under-engineered parts. it might as well be a fiat in that respect.



rubber has very specific physical characteristics. please do some reading on polymer cross-linking. it really will explain a lot more than i can here.



as for tires and shelf life, if you seal them up in an airtight bag, they can last a long time. if they are exposed to air, they harden. i've had quite a few tires go bad sitting on the shelf. it was very easy to tell too. the performance was significantly affected.

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[SILVY968]

DS968,



I did the 2K adjust, but did not do the 10K / yearly adjustment of the balance belt. I was not aware of this little detail, nor was I told or had I ever read about it on this forum. My Porsche periodic maintenance schedule only mentions checking tension 2K miles after replacement and checking them at 30,000 miles!



I have used this car as a DD since 2004 and have put 120K miles on it.

Flash said that you were supposed to check the balance belt, but I am concerned that it never came up or was done before. I have done 3 belt changes and have never come in for 10K or annual adjustments of the balance belt and have had no problems at all.

As the belt was not adjusted, and it stretched (shrink is not a possibility), I assume that a loose belt can split, but I do not clearly understand how this happens. Slip off a cog, yes, but split? Any comments?

Worried in Seattle,

Brian

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