Maximum mileage a timing belt will last?

Lot's of rapid acceleration & deceleration & running in a low gear as opposed to high speed cruising, running it where dirt can get in there & a misfire tends to be the harsh end of life. It's more dependent on vehicle design than anything else though, Pintos & 8V VW engines seem happy to do over 100000m, transit diesels & 20V VW engines seem to only just get past

How does that shorten timing belt life? The load on the belt is pretty constant in relation to engine revs.

My Nissan Bluebird did 90,000 on the first and 90,000 on the second both were still in good condition (recomm.is 60,000). I then bought a Bosch replacement instead of the after market type. The original power steering & alternator belts were changed at 180,000 stil in almost perfect condition! Quality plus good alignment and tension I guess. Older BMWs seem prone-a friends let go at 90,000 and wrecked the engine.

It's a similar situation to those rear chains on motorcyles-keeping an unsatisfactory technology for no good reason.

Then he only had himself to blame - IIRC no BMW ever reckoned on this sort of life.

The message from Duncan Wood contains these words:

As far as I can tell, the belt on my diesel Maestro has been in there for 133000 miles.

The message from Dave Plowman contains these words:

For the belt...or the whole car!

Load is pretty constant yes, but the torque that the belt transmits is proportionally dependant on engine speed.- at idle the belt is under the greatest strain whereas at high speed the power is still the same but torque demand alot lower.

Tim..

What? and you're happy to leave it there?

Rob Graham

Why is that? Once the camshaft is turning, whenever you're opening a valve, there's another one closing, which evens out the torque required. No?

My brother is determined to run my old 520 up to 1/4 million miles. But he changes the cambelt regularly. ;-)

Of course, BMW learnt the error of their ways and dispensed with rubber bands some 10 years ago.

The message from "Rob Graham" contains these words:

Yup. The car cost £300, is probably worth £30 and I CBA to change it 'cos I'll be changing cars in a few months anyway.

The message from Dave Plowman contains these words:

Yup. It's unlikely I'll bother to MOT it again...if all goes according to plan it'll be painlessly destroyed by then...possibly by cambelt failure.

In message , Dave Plowman writes

I had one in my Montego and I found a tear in the belt. Although it transpired that it had been there for over 1000 miles, the 1.5 mile drive to the Rover dealer was nerve racking.

The dealer reported that the cambelt had previously been removed and witness marks indicated that the belt had been pried off with a screwdriver. I had owned the car from new and it had been serviced exclusively by an authorised Rover dealer in Germany so there was no doubt who had done it.

The UK dealer submitted its report to Rover UK who paid for the replacement in full.

Some of the newer stuff has replacement intervals of over 80000 or 5 years, I think I saw one on Autodata that was 100000, the 5 year rule applies to all timing belts as this is the maximum life span of rubber.

That must be why all rubber fuel/brake/clutch/coolant hoses need replacing every five years.

The message from "Mark" contains these words:

They're like fleas on a junkyard dog.

Theirs a Marine version of this engine, so the engine alone if running would be worth something to the Hello Sailor brigade.

Dave Baker had a very good section in his website about the loading of cams actually being lower at mid-engine speed, rather than at low speed.

If this holds true for the amount of power/whatever the belt has to transmit, then the relationship between engine speed and belt "force" is a strange one.

I have to say I've learned more about engines reading Dave's site than any book. It's concentrated information!

Pete.

Chains are superior for reasons of efficiency of power transmission and manufacture. A belt would have to be prohibitively wide, to cope with the power-output of modern motorcycles. A belt-drive must be perfectly aligned too, or the teeth on the belt will be shredded, as I believe sometimes happens on the one current belt-drive motorcycle that I am aware of.