Mark's timing belt again

[Jonathan Coates <jon@domain.elided>]

Mark wrote

Date: Wed, 08 May 2002 11:16:21 -0400
From: Mark Denovich <mark@domain.elided>
Subject: Re: Mark's timing belt tensioner

> From: Jonathan Coates <jon@domain.elided>

> Now I thought I was cheap! Get a new tensioner AND a new belt. The belt
> could be damaged internally and if it breaks so will lots of expensive
> bits.

It wasn't a matter of being cheap, I haven't skimped on replacing
anything so far.   It was a matter of time/effort/waste.   I don't
necessarily see how a belt jumping a tooth due to a broken detensioner
automatically means the belt should be replaced.   It has less than 6k
on it.  By not replacing it I could save myself the effort of removing
all the stuff I need to remove/replace in oder to extract the old timing
belt.   Just replacing the detensioner would be significantly easier.

I've decided to go whole hog and replace the detensioner, belt,
water-pump, a few hoses, belts, etc...   So it's a moot point really.

I am pretty unhappy that a relatively new detensioner broke.

	--Mark

Now my alleged humourous tone obviously got lost there, so here's my 
serious tone response.
Timing belts are made to be espescially non-stretchy for obvious reasons. 
If they do get stretched they get damaged, heres why.
Inside the belt on what is called the neutral axis are fibres which are 
made from non-stretchy stuff (glass fibre etc) and this slice of the belt 
stays the same length all the time. Because it is hidden inside the rubber 
bit that we can see it is fairly easy to miss any damage which has occurred 
to it. ('Cos you cant see it)
If you imagine that the belt is made from a steel strap like you get around 
packages, then covered with rubber you will get the picture. When you 
overstretch the belt (like when it skips a tooth) you run the risk of 
damaging the inside bits. If the analogy steel strap is cracked then the 
belt will fail much sooner than expected. Short of x-raying the belt, 
(might work) I know of no way of checking a used belt.
So put on a new one.
HTH and sorry for any perceived rudeness.
Jonathan Coates
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