RajDatta

Actually, the S2 is notorious for sheering off it's cam chain tensioner right off the head. The 968 has a better design. As far as timing belt breaking, I would expect it to be less on a 968 because it's has a hydraulic tensioner. S2's use spring loaded tensioners for the timign belt, which have to be adjusted more often to compenaste for belt stretch.
Raj

JDS968

The thing to watch out for isn't so much that the timing belt will break, that's actually pretty unusual. Mostly they just shear off teeth, which kills your engine just as fast, but isn't as obvious before it happens.

Jfrahm

Yes, the 968 cams have fewer teeth than the S, S2 and 928 and if the variocam system can eat the cams if not properly maintained. The S2 cam chain tension generally is trouble-free if the pad or pads are replaced before they wear through or fall apart so it takes a commitment to neglect to allow that to happen. the 968 variocam ramps are more expensive and the replacement of the cam chain is a bit more involved, this should all be done by 120K or so, maybe a good inspection at 100K is wise. If the cams are fragging you can get them 'rebuilt.'

The constant cam belt tension on the 968 is a superior design so the belt is less of a problem. On the earlier 944 models the belt tension is locked down so it's loose when the engine is cold and tight when warm or just plain wrong all the time if not retensioned (or if a mechanic sets it super tight to let it wear in.)

-Joel.

RajDatta

+1 on the cam teeth sheering off. Most of the timing belt breaks I have seen, are from the BS belt breakng off, then getting stuck somewhere and eventually sheering off the timing belt in the process. The timing belt is quite strong but the teeth can sheer off.
Regards.
Raj

Rudey08

So ive sheared off 2, ( yes 2) 25 inch breaker bar drives battling the crank pulley so this weekend. And its not even Sunday. Has anyone done a timing belt / balance shaft belt job without removing the pulley? Is it possible

thomasmryan

A complete job requires the seal behind the crank cog...

Cloud9...68

It's very strange for the crank pulley bolt to be that tight - it's "only" 155 lb-ft (compared the what's affectionately known as the "Jesus bolt" on the BMW M62 V8, which is estimated to be somewhere in the 500 lb-ft range). It isn't a reverse rotation bolt - are you sure you're turning it in the right direction? And no, there's no way to do a belt job without removing the pulley.

RajDatta

Use a long pipe over your breaker bar and try to get some leverage. A 6 point socket would also be a plus.

Pcar968

Hey guys, I have always kept my 968 maintenance up. I am at 95,000 miles and had the VarioCam replaced and timing done at 78,000 miles. Entire front engine rebuilt at 54,000 miles, and previous stuff at 40,000 miles. My car has been garage for a few years, so as you can see I have not really put on a lot of miles since the last timing replacement. However, I just hit the four year mark today, so should I fear driving this month until I replace the belt? (I have been told 5 years and every 35,000 miles replace the belt.) I had the damper replaces two months ago, so that was heavy on my pocket :-D, and he checked my timing belt and said that it looked perfect. I'm just worried, and don't want a $1800 prob to turn into a $6000 problem LOL!


Thanks,
Richard

Cloud9...68

+1 on the pipe over the breaker bar - that's how I always do mine.

As far as replacing the belts after four years, I think you're probably good for another year or so. How often did you drive the car? Did it sit for months at a time? At the very least, if it hasn't been driven in awhile, I'd charge the battery, remove the coil wire and crank it for at least ten revolutions or so, just to warm up the belts a little, and to circulate some oil as well.

Pcar968

Thanks, I drive every month during the spring and summer; however, I just limit millage each year lol. My Porsche mechanic said the same thing another year so thanks for the reply. :-)

Rich

Jfrahm

Age (within reason) is no big deal for a modern belt. I just did a 928S4 belt that was at least 8 years old but low miles, it was perfect, supple like new. 35K is also more of an 8V 944 belt spec, those belts are narrower and the tensioning system is not adaptive. 48K is the book spec for the timing belt and that seems fair enough. I would probably be comfortable with 10 years 60K miles of normal street usage but at 40K or so I'd be looking for a reason to replace the belt during other work.

In your case I would expect the belt to last you until you needed front engine seals, valve stem seals, valve job, etc. Check your coolant and replace it if it has not been maintained well, there are test strips for the PH, etc. Rotting out the head gasket is probably more of a concern than your timing belt. It'd be a shame to need a head gasket or valve job after dropping for a timing belt (which would have to come off for the head work).

-Joel.

thomasmryan

Fishing out little VarioPad chips out of the oil pan does make one wonder about their longevity and failure mode. Dry starts after a car has been sitting must drag the pad against the rear perch (incoming chain side) forcefully. As they age and ductility fades, the brittle mounting edges chip so the wear from the chain is not the only good indication of replacement. My pads had 92k and not much of a groove from the chain. Yearly synthetic oil changes but the history is fuzzy over the last decade.

In my mind, radical dynamic changes in belt speed would be one of the main causes of shearing off belt teeth. For example, the 1000rpm jump from cranking to cold idle, pounding the rev limiter in 1st or 2nd OR when the tires hook up after spinning....things I avoid. I will trickle charge the battery overnight after a couple weeks of dormancy to keep the cranking speed up.

I will be lucky to put 5k a year on this car so I am going with the four year plan on the belts. Kinda feel sorry for the water pump bearings having such a side load from the timing belt tension while sitting...a double taper bearing would make sense in that application over ball bearings leaving a divot.

Pcar968

Thanks for the advice, My coolant is fine, I keep up with all my fluids. I replaced my radiator like a year ago, so it has been changed.