Red Flash

There is a sayin' in the commodities trading business: "A trend continues until it reverses itself."

That trend "going strong" will reverse itself at some point dramatically, if you don't change the belt and pump.

linderpat

15 years on an interference engine, and 30K miles. That's just poking the tiger. Change it. Is there other deferred maintenance on the car too? How often do you change the coolant, brake fluid, etc?

Adk46

Nobody here is going to give you permission. Not even me, who insisted a seller drive a car with a 15 year-old belt 200 miles to me before I would pay for it, and then found nothing badly amiss when I changed it. As you suggest, storage conditions matter (cool, dark, dry, ozone-free - good; outside in Phoenix - bad). But again, I'm not giving you permission. I'm coming up on my own five-year, never-mind-the-miles anniversary, but will not be seeking permission to extend it despite favorable storage conditions (and PKT). Someone might grant it, but only privately, whispered, with plausible deniability. I would not burden anyone to ask, though - my car, my risk, my eyes, my judgement.

ROG100

You can always use the "Long Life" Gates belt which is designed to last three iterations of the normal TB criteria. So 15 years or 150k miles.
As our cars are rarely used for high mileage the belt life is more pertinent. We have a number of customers well into the second iteration.
But as already said other components of the system are of more concern.

dr bob

Maybe an actuarial table for timing belt life and a list of the risks involved can help drive your decision.

Virtually every car manufacturer lists a life-expectancy in years or miles, whichever is less. Honda said 70k and 6 years until their latest cars equipped with a "maintenance Minder". Now a little over 100k but no years listed. Why? Because they extended-warranty the engine for 100k and don't want to have to replace all those belts "under warranty". On the years, the calculator in the Maintenance Minder doesn't have a calendar.

There's been debate on 928 belt change intervals, with most looking at 50k after the first one. Why? The original mileage was determined using ideal conditions for the belt, with all brand new components like rollers and gears. Those parts wear, and as they do they wear the belt more. So 50k is the colloquial limit here. On years, 5-6 years has been determined to be the life limit. Again, storage conditions and the driving environment contribute to the lifespan of the belt in years. The later/modern belts are Kevlar reinforced and may be less subject to memory and local stress fracturing after sitting. Still, it's a pretty safe number. My car lves in a climate-stable garage, doesn't get hot, and is driven gently. After a few belt changes I've settled on 6 to 7 years as the annual miles driven is now very low.

Failure modes: Belt stretches and doesn't break, allowing the belt to "ride up" on top of the gear teeth. Cam timing shifts, and often the extra strain breaks the nose off the driver's side (on US cars...) camshaft. The cams stop, pistons don't for a few revolutions, pistons hit the open valves, and the valves bend.

If the belt stretches and breaks before the nose of the cam gives up, you "only" have to pull the heads and replace all the bent valves. On your car the engine comes out for the head removal and the valve replacement. Engine in or out, heads-off means lots of "other" stuff gets needed service/replacement at the same time. It's a blessing for the car but gouges your wallet a little deeper.

All for the costs of the belt, tensioner, rollers and bearings, and often the water pump and the various drive gears for the belt. These costs are a fraction of the "recovery" costs needed for bent valves and broken cam, plus all the other "stuff" needed.

Jim Bailey, at the time with 928 International, once opined that a lot of insurance theft-recovered 928s had broken timing belts obviously incurred while a thief was joyriding in the stolen car. Wasn't a great idea at the time, and even less so now, as the amount of repair cost vs. the insurance company's idea of the value of the car makes it a total loss in their eyes. You lose the car, get not much for it, and oh by the way it's fraud.

Replacing the belt is just cheap insurance. You'll need to do it someday. The parts and pieces aren't getting cheaper. Just do it. You'll drive with less stress.

OTR18WHEELER

When I bought my car in 02/12, I didn't even know what model it was, just it looked cool.
from what records I had, I deducted the timing belt was last changed 18 years prior.
..searching DIY stuff I found rennlist, scared to death I took it to a local shop, ....when he inspected the belt, he was suprised the car made the trip., I'd been driving it for a few months, resetting the button almost every day.
Six years since then, now looking to replace it in the next couple years.
Roger has everything you need.

UKKid35

If only I'd changed the timing belt

In my defence when I bought the car there was a receipt for work to replace a camshaft just 20k miles earlier, and I couldn't see how anyone would change a camshaft without also changing the belt

I was wrong




What really concerns me now is that I don't end up posting a pic like this "If only I'd changed the fuel lines"

However changing the hard lines at the back of the car looks way beyond my capabilities

oups59

I didn't know that. This is not on their website - only show the standard T196. What is the price difference between the long life and the normal T196?

Wisconsin Joe

The belt on my 928 was about 8 years old, maybe 20k miles. I took it off when I did the cam seals, and for $40, there's no way I was putting the old belt back on.
The belt looked fine.

OTOH, I just did the belts & rollers on my 944 last winter. They had been on since I bought it in 05. 13 years and 25k miles. Again, the belts looked ok. No real wear/damage.

Are you planning on doing it yourself, or paying a tech to do it?

At that age, I would change it. For peace of mind if for no other reason.
Even if you pay to have it done, spread the cost over that long and the 'per year' cost will be quite reasonable.

NIACAL4NIA

The 928

worf928

I've done a lot of timing belt services on 928s and have had the opportunity to do more-than one belt service on many 928s that have been under my care for 10+ years. I've seen first-hand previous 'belt-service' done poorly and the results. I've seen belts with missing teeth. Cams off by several teeth because of under tension. I doubt I've seen it all. But I've seen a lot.

Here's a theory (mine):

The belts don't just break unless they are so old that they've dry-rotted. (And I've never seen a dry-rotted belt. I've heard that other people have seen them. I've held in my hands 15-20 year old belts last touched at the factory and they all look better than the worst of the 'just changed' belts I've had to re-change due to the previous technician.)

When a 'timing belt failure' occurs it is always due to some other part it touches - or the previous technician - being the primary failure mode. I would very much like to hear from someone that has torn-down a 928 engine after a 'belt failure' where this was not the case. (The exception to this might be non-Gates/Porsche belts. Maybe Chinese knock-offs snap like old twigs.)

Yes, the belt should be changed periodically, but every single part of the timing belt system needs to considered as part of the service:
- The two rollers with sealed bearings need to be replaced, How long does a sealed bearing last? Is it just a matter of usage? Or is chemistry of the grease involved? I have read several papers that lead me to believe that a sealed bearing is 'known good' for about 10 years due to chemistry.
- The plastic bushings on the roller carrier very-likely need to be replaced.
- On a pre-mid-'87 the pivot bolt for the carrier should be checked and replaced if it isn't true and then probably anyway due to fatigue.
- The tensioner needs to be rebuilt to ensure that it will retain all of its oil until the next belt service.
- How do the gears look?
- Water pump?
- What tension measuring tool is to be used?

Short story: It's NOT the belt. It's not the lifetime of the belt that matters. Changing JUST the belt is a waste of labor and brings with it a sense of security that is false.

GT6ixer

NIACAL4NIA

Cheap R12 Freon from Mexico and modified fuel pressure regulators also causes fire. Didn't pre 1985 use rubber fuel injector hoses?

paalw

I think you got that spot on. What about the time-frame-change-after-5-years-or-whatever perception? Is it correct to say that this time frame perception is mainly because the belt is made of rubber, and rubber ages? But if the rubber is that good, and also reinforced with who knows what, chances that something would break only because of age is minimal? Are there other things in there that is getting "worn out" only by age and not usage?

GregBBRD

I tell everyone the same thing:

I "redo" more timing belt jobs than I start, by a factor of 4 or 5.

Cheap belts, cheap water pumps, not replacing the other components, worn out gears, poor workmanship.

For as "simple" as people think this job is....it apparently isn't.