NIACAL4NIA

A friend of mine replaced his 944 belt and waterpump before the 45k miles and 4 year interval and the belt snapped within 1000 miles due to a defective waterpump. I've seen Porsche 996 owners replace a perfectly good ims bearing and had their engine destroyed either by a defective part or a bad install.

Christopher Zach

Having been through two timing "failures" on my 87 944S (the 4 cyl version of the 928) I do have a few thoughts on the matter.

The first failure was at 50k or so and was due to the belt snapping at idle. Bent 12 valves I believe, root problem was that it had a -00 type belt. The first gen belts that Porsche used were... poorly made, and had a tendency to snap. Thus they released the -02 and things got a lot better. Still, you replaced it every 40-60k miles, which I did religiously.

The second event occured at 180k or so when I started the car and the engine blew up. Bad sounds, shutdown. Had it towed home, thought it was the belt, pulled the front, belt (which I had replaced 20k miles before and re-tensioned 3k miles afterwards) was fine. Pulled the head and saw that the timing chain ramp had failed, resulting in the intake/exhaust chain catching, breaking one of the camshafts, shearing teeth off the other, and ripping the tensioner right off the head...

Took a year of patient working from 5am to 7am (after feeding baby and before work) to remove the head, R&R everything, replace the valves, put it all together, etc. It was a pain in the ***.

I think the first generation belts on the 928 had similar problems, later formulations are better thus the reduced number of broken belts. I'm worried about the chain tensioners, but it has been pointed out that they fail at around 150-180k miles on 944's which run the engine about 33% higher rpm at cruise anyway. So a problem, but not as bad.

My belt has about 30k miles on it, about 4 years old, and I have the docs to show it was replaced along with the pump. I'll pull it in the spring, replace it, and pull the head covers to have a look at the pads.

NIACAL4NIA

According to a Porsche mechanic the 928 chains have a lower failure rate than 924s and 944s due to the engine design. True that belt technology is much better. I believe engine operating hours is much better than miles or years considering the climate you're in..BTW my original belt on my 1986 Porsche was replaced in 1997 @ 100k miles due to a water pump leak.

Dmhager

Sharing a recent experience changing out the timing belt on a 40k mile 1988 S4. This low mileage car was pretty much a time capsule: all original and in near perfect condition (not one single dash crack, all original paint, unmolested under the hood). The second owner had the car from 1991 until he passed in 2019, which is when I acquired it. The car spent most of its time in Alaska (originally sold in Alaska) and some of its time in the SF Bay Area. I had no records on the last timing belt change, but it had last been checked an adjusted by Stevens Creek Porsche near SF in 2001. I was amazed at the lack of age deterioration on the rubber parts throughout the car ... I knew the Bay Area climate is kind to cars and apparently Alaska must not be so bad either if its kept in a reasonably climate controlled garage during the dark months.

Now on to the timing belt: what I found was a Uniroyal branded timing belt that appeared very old (never seen a Uniroyal belt so I started doing some research). It showed some cracking on the tooth side in the corners of the teeth. The timing gears, oil pump gear and crank gear were perfect with no signs of wear and the timing belt was still in proper tension when I removed it. I thought it might have been the original belt until I saw that the car had rebuilt Porsche WP so Im guessing it must have been changed sometime in the 90s, BUT that Uniroyal timing belt must have been older and maybe much older. Uniroyal was the original supplier of belts to Porche (not sure if the pre-HTD belts were Uniroyal, but they certainly were in the 80s) and sold the power transmission business to Gates in 1986.

So, how old was the timing belt I removed?? Im guessing probably not much newer than 1986 since Im assuming they would have been branded Gates shortly after the acquisition. Or it could have been older and sitting around the inventory of some shop in Alaska. My guesstimate is that the belt was somewhere between 33-35 years old and had been on the car for nearly 25 years and was still doing its job although I dont know how much longer those teeth would be hanging on.

As for the rest of the TB related stuff I found: surprisingly, the rubber boot on the tensioner was soft (when have you seen that on long neglected S4?), the large and small rollers were all fine, the water pump showed no obvious signs of deterioration and the plastic bushings on the tension arm showed no obvious signs of wear or deterioration, and finally, there was still some oil in the tensioner. I must confess that this was the most enjoyable TB job Ive done on a 4 cam car as it was clearly treated carefully be skilled hands in the past (I almost never find that on an S4 that has had a few timing belts). After this enjoyable little archeology dig, I replaced all of those usual servie items (giving them a proper burial for the fine job they had done), rebuilt the tensioner, put on a new Gates belt and water pump, and then spent an hour or two trying to getting that little freakin' bolt lined up and started to hold the engine harness and ground to the passenger side engine/cam cover bracket.

PS - I am in no way suggesting that anyone trust their belt or other bits for 25 years, but clearly if a proper TB/WP service was done, you should be confident that there is some margin if you follow the standard change interval.

928 DesMoines

Good to know. Gives me sense of relief, mine isn’t quite due, but I was stressing a little. Probably this winter.

NIACAL4NIA

Starting in 2000 engines switched to EPDM Timing belts vs the older Neoprene belts. EPDM last twice longer about 100k miles without cracking but do shed rubber like tires. EPDM can handle higher/ lower temp so a new Gates or Contitech belt purchased after year 2000 is gonna last longer than the original Neoprene Porsche belt.

hacker-pschorr

5 years later, still haven't changed the belt in my 79 and yes I do drive it.

Further digging into the history of this car since my last post, the belt was mot likely installed sometime in the mid 90's

....one of these days buying two more 928's since that post interrupted things.

No, I would never take such chances with a 32V.

928NOOBIE

If I had a practice engine I'd love to try it, but I'm not going to learn on the engine thats in my car; just not willing to take the risk. If I can't afford to have the service done by the right folks here in KC/OP area it would either be parked or sold.

That being said, it's in a heated/cooled garage and I am considering going to a 7 year replace rather than 5....

NIACAL4NIA

My belt(contitech) is 17 years old with less than 30k on belt. and was installed in 2003 including rollers, waterpump, and tensioner rebuild. Last inspected the belt looked fine and I'm not worried since I'm going to put an electric motor from EV west in Southern California. They have kits for around $7500. Mine is a 1986 32 valve manual transmission.

928NOOBIE

That sounds pretty cool....so the batteries, motor and all are included? How are you handling the transaxle?

ddire333

When doing my recent "rescue project" i found a Porsche branded belt stalled (which still looked and felt good, hard to see difference to new) and from service records / & date on water pump it was 1995 when last done so pushing 25 years & 70k miles. While I have since changed, it was the tension-er / idler and water pump bearings which were all showing more wear then the belt, so while I wouldn't risk a belt that old, they seem pretty robust, and i would guess the other elements in the system are more likely to let go, impacting the belt.

worf928

On 928s, timing belt failure is never due to the belt failing. It is always due to the previous technician failing.

James-man

Therefore I would definitely worry if the next technician is ME.

NIACAL4NIA

A 944 owner broke a timing belt due to a defective waterpump less than 1000 miles after installation. Google EPDM vs older neoprene belts.

worf928

This is about 928s. Not 944s.

944s are vastly different in their failure modes. Apparently(*).

Nevertheless, I’ll play. Was the 944 water pump a defective Porsche pump? Or a defective rebuild? Or a no-name pump from the equivalent of ‘ebay?’ Did he install the pump and belt himself?

I won’t dispute that modern belts are better.

I will say that the original belts are fine too.

I have a collection of a about a dozen 928 timing belts that I keep for ‘show and tell.’ One of them is a belt that was put on by the factory that I removed 17 years and 40k-miles later. All of the other belts have less than 5 years and 5 thousand miles. Most of those are actually 2000 miles or less. The 17/40 belt looks new. The others all show deterioration characteristic of certain ‘technician failure modes.’

Yes, timing belts break, but it is always a secondary mode. They do not simply break by themselves. A stronger belt doesn’t solve a problem that exists.

(*) After living the reality of 928s for 20+ years now and comparing that reality with ‘Internet’ legends of 928s, I assume that the 944’s legendary unreliability is also 50% poor diagnosis, 40% telephone game, and 10% truth.