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Cam drive belt - Printable Version

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Cam drive belt - KesslerR - 09-06-2011

I have several questions with regard to the toothed belt driving the overhead cams on our 968's.



First, is the 968 an interference engine? If the cams stop going around while the pistons are still going up and down, will the valves left open hit the top of the piston?



Second, can any of the Forum members actually provide some mileage numbers of when a belt has failed?



Third, and related to the second, can anyone give some lifetime numbers to when a belt failed?



Its not that I want to stretch the life of the one in my 968, but we all have some different conditions our engines live in. Some have extreme heat, some have extreme cold, some have been exposed to oil, and some have set more than run. It would be interesting to know the history of some belt failures.

Cam drive belt - ds968 - 09-06-2011

1. yes



2. 50k miles post last belt replacement, but the belt was also over six years old. The failure happened at the end of a two day driving event where the outside temperature went from a 105 F day to 45 F night to 100+ again the next day which I'm sure contributed to it.



However, even though the manual suggests replacing the belts at 60k mi ( I think..) and makes no mention of " and/or " a timeline, I think most of us here would caution against waiting anyway near that long. I'd say MAX. 40k miles or four years, whichever comes first.





Cam drive belt - 94SilverCab - 09-06-2011

I drive my car roughly 3,000 miles per year in the Mid-Atlantic. As a result I don't drive mine enough to get to the mileage recommendation. WITHOUT FAIL, I will replace my belts every 5 years at the maximum.



Regards,



Jay

Cam drive belt - Scott Collins - 09-06-2011

I just replaced my timing belt, which had 4 years and 32k miles. I drive the car every day, just about, and it runs in all seasons, here in Central NJ.



Both belts actually looked very good, and the timing belt had just a bit of glaze, and a small bit of fraying in one spot on the edge. I could definitely have gotten another year and 10K miles out of them both, and probably 20K miles out of the balance belt, but I'd rather replace them early then replace them later, along with valves, guides, head gasket, etc. You get the picture...



My biggest concerns with the timing belt are age in terms of years and oil getting on the belt and degrading it to the point of failure. I think that oil is a real problem, given that right near it there are 3 oil seals, any of which can leak and cause oil to get on the belt(s). The oil filter housing gasket is probably the most usual offender of oil leaks, big ones, but it doesn't affect the belts since it sits on the side and low, and during driving, air should push any oil leaking back from the front.



It sounds strange, but I think that the belts, along with many other things like oil seals, do better when they are run on a fairly regular basis. Sure they wear, but my hunch is that they stay more pliable and are less prone to cracking.

Cam drive belt - sstman - 09-10-2011

I have just had the belts and rollers changed on my car, along with the oil filter housing seal, and lower balance shaft seals which were 'weeping' a little, car used daily, and now showing 145,000 on the clock. Balance shaft belt now 'singing' a bit, but it goes away after a few miles. <img src="/forum/images/smilies/968/EmoticonCar.gif" class="smilie" alt="" />