Maximum mileage a timing belt will last?

Greg> Whats the maximum mileage a genuine timing belt will last? Greg> Would any particular conditions affect how long it would Greg> last, or make no difference?

Well, it might last forever. But every car I've ever seen recommends replacing them at LESS than the service interval because the cost of it breaking will be loadsamoney!!!

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No. There's two pulleys isn't there? One of them is on the crankshaft. That's the one that increases the stress on the cambelt.

On a motorbike, a belt is a much better way of transferring power from engine to wheel.

As a chain wears it becomes incredibly inefficient - you only have to touch a chain after a long run and you'll realise just how much power is being wasted.

Other advantages are that they're pretty much maintenance-free - re-tensioning is done at thousands of mile intervals rather than hundreds with a chain (chains get worse as they wear - towards the end of their life you can be adjusting them every hundred or so miles). And you don't have to lubricate a belt.

The only reason belts aren't more commonly used is that is't prohibitively expensive to make a belt that will take the power from any reasonably sized bike. However, BMW have pretty much got it sussed on their big single trails / commuter bike thing.

I predict that one day belts will become commonplace.

??

Did you even read/understand what I wrote?

No. Cams don't work very well backwards, they exert much of the spring force bending the camshaft and very little turning it. It's sort of like a screw - try getting the screw to rotate by pushing the nut along it. Reaction torque on cam is not spring force x lift. It's spring force x offset distance from valve centre to the point the follower contacts the cam at. At peak spring force when the valve is at max lift the offset is zero. All the force goes on bending the camshaft. The offset will be max at about 1/2 lift but the offset is less than 1/2 lift.

-- Peter Hill Spamtrap reply domain as per NNTP-Posting-Host in header Can of worms - what every fisherman wants. Can of worms - what every PC owner gets!

Nope, it's lossy & you don't get the inertia of the valve back. There's a nasty resonance chart so at some speeds you get worse losses than at higher speeds as well. Also you have to accelerate & decelerate the camshaft itself , etc.

No. Why, was there something important in it? ;-p

There is no five year rule for rubber in general. Rubber which comes into contact with oil however is a whole different ball game.

The Haynes manual for my Xantia recommends 3 years or 36K miles, although Citroen recommends 72K miles.

-- James

Is 72K what's in the owners manual or what is on the TSB that your dealer has failed to tell you about? What's printed in the manual that comes with the car is often found to be very optimistic a few years later when lots start breaking.

-- Peter Hill Spamtrap reply domain as per NNTP-Posting-Host in header Can of worms - what every fisherman wants. Can of worms - what every PC owner gets!

Tru but Haynes tend to be pessimistic, e.g. 2.0 8V VAG engines aren't an interference design & I've never heard of one snapping a cam belt so doing it twice as often seems pointless.