[ds968]

Yes, 185 K miles on a timing belt, not a chain. Just passed that mark, and on top of 185 k miles the belt has been in the car since 1998, so about 18 years.. That said, no it's not one of the 968s, lol. It's in our Pathfinder . Nissan recommends changing the belt at 90 K miles. But you guys know me, lol. So I called the local Nissan service center and asked them if they think I should change the belt , considering it is also an interference engine and if it snaps the result won't be pretty. They said sure, that I should change it now since it's overdue by more than double the mileage suggested by the mfg. They charge $ 800 for the whole job., P&L ( mostly labor, unlike our cars the belts are cheap ) That was the official response, and then unofficially the guy said they've never heard of a belt break and some of their customers have half a million miles on their cars ... Which leads me to the question : why can't Porsche ( Gates, Conti, Dayco ) make our 968 timing belts like that ?! I think the Nissan OEM for belts were / are Dayco , but not sure.

So tell that me Porsche did not deliberately have these belts built to specs which would not last more than 45-50 K miles , and 5 years or so , just so they can support their parts and service business ...and I won't believe you. :-) :-)

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[flash]

it's simple physics.  i could do the math for you, but it would take an easel, charts, graphs, and a whole lot of cabernet.  basically we have a system designed for a 2 liter engine with a little over 100hp.  it really didn't change when they added more than double the power and associated heat.

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[ds968]

So they just figured they'd save money by not having to completely redesign the belts construction and remanufacture a different product aligned with the HP and torque of the 968 ( heck they could have at least used Kevlar, the technology was certainly there at the time ) and took the let the chips fall where they may attitude , knowing that either the owners will frequently have to spend a lot of money replacing the belts, or spend a hell of a lot more money fixing the damage caused by a broken belt - either way, win-win for Porsche and the businesses supporting its parts and service domain. And just because the belt is simply wider than the one for the 944 they can point to that negligible modification as proof that a change accounting for the difference in power was most definitely made . Ugh. Porsche's engineers are far from stupid and that's what leads me to suspect this was not just an economic maneuver at the front end, but done with full knowledge it will be a gift that keeps on giving ..

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[ampegboy1]

When I took the Polo in for a (way overdue on 'time' but not too bad on 'miles') belt change, I asked the chap at VW to leave the old belt in the passenger's footwell as I was interested to see how it looked after so long. He said that it's more common for components driven by the belt to fail and take the belt with them, than for the belt to fail on its own. Case in point - the water pump on my dad's 2001 Passat seized the other week on the motorway, shredded and snapped the timing belt and took the engine with it. Changing the belt regularly gives you a chance to check the other driven components as well and reduce the likelihood of catastrophic failure.

 

Michael

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[ds968]

I think that's why it's recommended to change the rollers if not at every belt change, certainly at every other belt change, as well as the tensioner at that time ..

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[wildcat]

Well not to cause shivers to run down the backs of perfectionists but I'm sure my belt has over 120k and doesn't look any worse than the one I planned to replace it with. If it ain't broke don't fix it. I realize this is a gamble but then I'm still running the M.A.F. with my bubble gum repair and the car is running better than ever.  (I took out the flimsy grill in the front that goes around the tow bar slot and I can tell you the engine breathes even better.)

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[94SilverCab]

120K on the same belts? You need to buy a lottery ticket...

 

JMHO,

 

Jay

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[Ryan]

Porsche changed the timing belt on the 944's when they came out with the 944S (first 16 valve engine) It went to a wider belt to shoulder the added work it had with the additional cam. The 944S2 and 968 all use this belt.

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[Bulti]

it's simple physics.  i could do the math for you, but it would take an easel, charts, graphs, and a whole lot of cabernet.  basically we have a system designed for a 2 liter engine with a little over 100hp.  it really didn't change when they added more than double the power and associated heat.

I assume your refer to the 924's Audi block? I would like to see some evidence of our belt system being related to the 2 litre. Our block is in essence one cylinder bank of the 928's Porsche V8. It has nothing to do with the unit in the 924.

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[flash]

the timing belt system design is essentially the same

 

as for the widening of a belt, yes, they made it 2mm wider.  still not enough as it turns out

 

the bottom line is that the system is under-engineered.  that's why it fails so early.

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[wildcat]

The rubber is solid and not dried out, the chord has not separated anywhere along the belt, the "teeth" each have a small indentation at the bottom, (where the outside of the belt is the top), there is no appreciable wear in that little groove or missing pieces. I don't play the lottery and that may explain it. 

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[94SilverCab]

My car was at 56K, and I vowed that I would change the belts at 60K...didn't make it...

 

Jay

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[ds968]

My belt snapped at about 59 K miles, and it was in the car for 7 years at the time , but no clue how long it might have sat on the shelf before it went in the car .  ( Gates recommends their distributors not to keep the belts on the shelf for longer than 6 years , but there is no enforcement of that "suggestion" , so it's merely just that ..a suggestion )   Now, in all fairness, the 59 K miles driven by yours truly were probably the equivalent of at least 100 K miles of "normal driving" by most sane individuals . In those seven years, I had almost never let the RPM drop below 4,000, even when peacefully cruising on the highway, and usually shifted at a hair under the red line all the time, so the belt took  a lot of undue abuse.  Also no idea if it was Gates, or Dayco, or Conti ( ugh..) , as the PO had it installed before I bought the car and he did not know what brand the shop put in. , not do I know if a roller or tensioner failed  causing the belt disaster. It was shredded to bits, lengthwise, like string cheese, lol  and eventually broke at one spot where the wire or whatever synthetic fibers they use inside the belt could not hold it intact.  Oddly enough the balance belt was in absolute perfect shape and still in place  !   

Anyway, although you may get lucky and your belt could very well last 25 years or 100 K miles,  you're making a  $ 6,000 +  bet on that .   And while belts failing prematurely is not common, it's never fun becoming part of that club no matter how much the statistics may mislead you into a sense of confidence.    I wish I remember how often I changed the timing belts in the 944s.   I logged over a quarter million miles on the car , and pretty sure I replaced them at least once, possibly twice.          

 

As always, the obligatory caution : YMMV :glare:   !!                    \

 

But back to the original post - why do Nissan or other cars belts last hundreds of thousands of miles...and not ours ?   I definitely side with Flash's inadequate engineering theory, and take it one step further into likely the deliberate apathy territory. ..        

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[flash]

you CANNOT ascertain the status of the belt by any visual means.  feel is no better.  the problem is in polymer crosslinking.  the belt loses its elasticity over time.  all it takes is exceeding the elastic component of the belt, and bingo - new valve train required.

 

high rpm running will strain a belt, as the increased friction creates heat.

 

one of the most stressful things for the belt is starting the engine.

 

wide temperature swings will also put stress on the belt.

 

ignore at your own peril the repeated advice of those who have guessed wrong

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[ds968]

" wide temperature swings will also put stress on the belt."


Oh yeah, I forgot to mention this but , IMO , another thing which should not be overlooked - my unfortunate experience happened at the end of our annual Paso Robles meet, during a heat wave with day temperatures exceeding 100 F and during the night ( which we spent on the coast ) the temps dropped below 40 F...only to go back to 105 ( IRRC ) the next day . That second day also happened to be our designated spirited drive run and goes without saying those runs tend test our cars' maximum performance tolerances ..ahem .. So combined with my aging and high mileage belt, I am convinced beyond much doubt that the huge swings in temps causing that belt to expand and contract and expand again, and furthermore being subjected to a lot of high RPMs, was probably the last nail in the coffin. Consequently those of you who live in desert environments ( AZ, NV, Palm Springs Ca, etc..) where temp swings are typically pretty big between day and night, should consider replacing your belt even more frequently than the prescribed intervals mentioned here ..or, you're increasing the chances a nasty surprise ..

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[wildcat]

you CANNOT ascertain the status of the belt by any visual means.  feel is no better.  the problem is in polymer crosslinking.  the belt loses its elasticity over time.  all it takes is exceeding the elastic component of the belt, and bingo - new valve train required.

 

high rpm running will strain a belt, as the increased friction creates heat.

 

one of the most stressful things for the belt is starting the engine.

 

wide temperature swings will also put stress on the belt.

 

ignore at your own peril the repeated advice of those who have guessed wrong

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[wildcat]

Whoops, didn't get my content in. I cannot disagree in general. Those that have SC's installed must take additional caution!!! I'm just saying it is possible.  I've got two years on tires I'm now replacing, roughly 30k on them and the belt has outlasted them by a wide margin. 

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[flash]

the SC has little to nothing to do with the issue.  in fact, those with an SC could possibly get MORE belt life, as they would not be revving as high, therefore reducing friction and heat.

 

it's possible to win the lottery too, but the odds are not in your favor

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[wildcat]

I disagree on that. The SC puts alot more stress on that belt as does the additional H.P. but enough on that.

 

I have the belt. And I intend to install it shortly.

 

I will also show the tire which did not outlive the belt because I think its interesting in contrast. You may not agree and that's o.k. too. 

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[94SilverCab]

I was kinda hoping you would run that belt until failure...there's a few parts from your car I could use 

 

Jay

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