Re: Timing belt broke after 50k miles?!

>Ah. I'd never heard that term before. I see the difference: 
>http://www.gates.com/brochure.cfm?brochure=2256&location_id=3487&go=SearchGatesPopular

>has diagrams which show how for a non-interference engine, the valves and

>piston never occupy the same space whereas for an interference engine
they 
>overlap though never at the same time! I'd thought that *all* engines
were 
>interference type.

In my narrow minded way of thinking no normal street engine should
have a timing belt and be of an interference design.  Unfortunately
nobody asked me when they designed them so I guess my opinion doesn't
really matter  :-)

>Interestingly the belt split lengthways, with only half the width
breaking 
>in two. So the belt didn't just fall off into the road and was still
there 
>to be examined when I stopped the car. The ridges that engage with the 
>crank, alternator and power steering pulleys had tiny cracks across them 
>every millimetre or so, as if the rubber had perished. It was the idler 
>pulley rather than the crank pulley which was damaged on the first
occasion: 
>it looked as if it had ****fted sideways on its shaft and scraped against
the 
>engine housing.
>
>Mind you, as far as I know, the belt had never previously been changed at
a 
>service - and the car had done 120 K miles. I wonder if it should have
been 
>replaced every so often.


The belt probably should have been replaced before that mileage but if
the idler pulley failed it wouldn't have mattered... It would eat the
new belt too.  The ridges can be cracked and the belt still be good.
If any of the ridges come off or you see wear anywhere else on the
belt it needs to go.  Usually a tensioner will make noise before it
fails but not always.  

>
>As a matter of interest, while the belt is off before it is replaced, how

>easy is it to tell whether the crank pulley is damaged? Would it wobble
from 
>side to side on its shaft? I'm assuming that the ridged surface of the 
>pulley was undamaged because surely a garage would spot that as they were

>fitting the new belt, even if they didn't notice that the pulley was
loose 
>on its shaft. 
>

It depends on how the crank pulley failed.  On most cars that I have
dealt with the crank pulley is bolted very very well to the crank
shaft  A failure of that pulley is pretty dang rare though the
harmonic balance is behind it / part of it on some cars and those do
fail more often  Do you know what piece of the pulley actually broke?
On lots of cars you can just see / feel enough of the crank pulley
from the top to loop the new belt around it so I don't know how easy
it would have been to spot the problem on yours before it happened.

        Steve B.