[cosimo]

Just a word about changing your timing belt at 30K miles. I let mind go for 40k and now paying the price. Not sure if the valves are toast. I've had a real rash of probelms lately, overheating (needed tow), check engine light on(knock sensor), hand brake not working, and now the timing belt(needed tow). I have 141K miles. Also in need of a new clutch (70K on the Sachs

clutch),a bad motor mount, a leaky oil pan gasket. Need I say more. Going to get everything fixed eventually, it's just a bit frustrating right now.

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[flash]

how many years were on the belts? that's really the important part



also, did you have the balance belt retensioned each year?



what brand of belts were on there?

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[94SilverCab]

NEVER, NEVER, NEVER more than 5 years or 15,000 miles, whichever comes first, under any circumstances. Most would recommend even more frequently, I'm talking the outside limits....



JMHO,



Jay

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[Cloud9...68]

15,000 miles? Really? That's the most aggressive schedule I've heard so far. But on the flip side, I'd say 5 years is too long - I would recommend 3.

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[ds968]

Changing at 15,000 miles is borderline insanity...unless you also have 4 or 5 years on that belt, in which case you better replace it.

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[flash]

i think he meant 45k.



3 years in areas with wider swinging climates. 4 years in moderate climate. less on both if you track the car.



and don't use continental belts

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[ds968]

And less if you have a SC - a hell of a lot of torque on the belt, that's not a good thing on longevity :-)

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[JWahlsten]

What Flash said. 4 years or 45k... For me 4 years if street only. Every other year for a car taken to the track. Make sure to check/replace rod bearings too!

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[Cloud9...68]

[quote name='JWahlsten' timestamp='1403987252' post='159243']

Make sure to check/replace rod bearings too!

[/quote]

Oof... A belt change is one thing, but rod bearings are a whole 'nother beast, requiring removal of pretty much everything but the paint. OK, I exaggerate slightly, but getting the oil pan off requires removal of the cross-member, which means disconnecting the engine mounts, which means supporting the engine from above, plus an alignment when it's all done. Easily a $2 - 3K job if you have someone else do it, or not much less than the cost of a used engine. I know certain years of the 944 had issues with the No. 2 rod bearing, but is there solid evidence of a similar problem with 968's? I rebuilt my engine at 115K miles, and the rod bearings were actually in very good shape, despite a fair amount of track use.



My feeling on any type of maintenance is that it's like buying insurance. Usually the cost of the maintenance (insurance policy) is far less than the cost of what it is you're trying to protect, making it a worthwhile endeavor. But I don't see a rod bearing replacement falling into that category.

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[JWahlsten]

Copy. Maybe they finally got the oil pressure right to the number 2, but I have seen and heard of failures. I'm not sure that all were related to number 2 as some were related to the dreaded cracked oil pickup...



You may be right. Maybe I am overly conditioned having driven so many 944 variants.

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[Cloud9...68]

Never a bad idea to be concerned. I had my oil pick-up tube reinforced with a support pieced brazed to it, and I had my crank cross's rod journals-drilled, per Mike Lindsey's recommendation, just to be safe.

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[94SilverCab]

I drive my 968 3,000 miles/year...I go 5 years. My first belts went 8 years, 56k before wiping out my head. <img src="/forum/images/smilies/968/sad.png" class="smilie" alt="" />

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[ds968]

[quote name='94SilverCab' timestamp='1404045625' post='159278']My first belts went 8 years, 56k before wiping out my head. <img src="/forum/images/smilies/968/sad.png" class="smilie" alt="" />[/quote]



Very close experience to mine : under 7 years, 58 k miles , but driven 90% of the time above 4k rpm and on top of that with frequent snap acceleration m.o., not the gradual acceleration kind which tends to be a little less stressful on the belts. The balance belt was like new, the timing belt was shredded to bits . No idea if they were Conti or Gates or Dayco. I replaced the belts with Gates, after doing about as much research as I could on the topic. Per Gates engineers' statements, the impact on a belt longevity is much more a factor of mileage than it is age , about 80 / 20 , but eventually age will take its toll, all by itself.



But do check your balance belt tension periodically, as flash suggested, because unlike my experience which I understand was the exception to the rule, it's the balance belt in most cases that goes first by getting loose and possibly cut by the pulley and then it takes out your timing belt .

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[flash]

5 years and about 25k miles here when my balance belt shredded and nearly took out my timing belt.



belts age on the inside at a molecular level. you can't always see it. the bonding changes over time, reducing its elasticity (i posted a paper on this somewhere here that explains it a lot better than i can). that is the problem on our car, which seems to be an anomaly. while the gates guy would normally be right, when it comes to the 968, elasticity seems to be extremely critical. i think the porsche engineers really blew it when they failed to take into account the engine size, power, and heat increases, when deciding not the change and improve the belt system. they did add a hydraulic tensioner on the timing belt, obviously realizing that the belt needed more regular tensioning than the previous system would give it, but i don't think they went far enough. the number of failures would seem to bear that out.

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[PorscheG96]

Ron, did you ever perform scheduled re-tensions of your balance shaft belt over that 40k miles?

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[ds968]

They should have used a timing chain in these cars, not a belt !

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[flash]

i agree. i have a design in mind, but have not had the time or inclination to finish it.

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[ds968]

And one more thing on the re-tensioning or change frequency - those who deive in climates with extreme temp swings from day to night

( deserts, valleys, etc. ) should pay even closer attention to their belts. Although my belt went after a lot of high stress mileage and age, the failure happened after two consecutive days of 100+ daytime and 40 nighttime temp swings. By all accounts that played a significant role in the belt finally giving up - expanding and contracting and expanding again is not your belt's friend ::-( .

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[94SilverCab]

I have my belts retensioned after 2,000 miles (it's part of the service, so $0). Then have them checked yearly.



Jay

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[flash]

yup - that's right

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