>>First of all, what's an "interference engine"? I've never heard that term
>>before.
>
> www.google.com
Ah. I'd never heard that term before. I see the difference:
http://www.gates.com/brochure.cfm?brochure=2256&location_id=3487&go=SearchGatesP
opular
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.
>>On a related note, I'd like to know how a garage can examine my fan-belt
>>(well, alternator and power-steering belt) amongst other things at a
[quoted text clipped - 15 lines]
> In your case the belt probably did look fine, the crankshaft pulley
> was damaged and chewed hell out of the old belt pretty quickly.
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 shifted 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
> new belt lasted a bit longer just because it was new before the same
> damaged pulley got it. A damaged crank pulley is a pretty rare thing
> so the shop didn't notice the damage (on some cars you can hardly even
> see the crank pulley from above). Crappy situation but it happens.
Yes. When it happened the second time, I'd driven a long way the day before
without any problem, then within a mileor so of setting off on a long
journey the next day there was a clattering chugging noise (I thought there
was a tractor behind me!). This seemed to get worse whenever I came off the
power. I limped back home again, with the ignition light occasionally
flashing on (a sure sign that the belt had problems) and as I turned into
the drive, the noise became much louder. The belt was intact but looked as
if it was covered in very viscous oil - my first thought was than the crank
pulley bearing had gone and engine oil was leaking out, which would have
been expensive! It seems that the viscous black goo was molten rubber from
the belt.
A nice little bill - an extra £250 that I hadn't bargained for, on top of
the previous bill for this amount when the belt failed the first time.
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.
Steve B. - 06 May 2008 17:00 GMT
>Ah. I'd never heard that term before. I see the difference:
>http://www.gates.com/brochure.cfm?brochure=2256&location_id=3487&go=SearchGatesP
opular
>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
[quoted text clipped - 8 lines]
>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.
Mortimer - 06 May 2008 17:25 GMT
> 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.
Ah, so it's acceptible to have a belt where the longitudinal ridges have
cracks at closely-spaced intervals all the way round the belt? OK. It looked
as if it was badly perished, but maybe it was still serviceable.
>>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
[quoted text clipped - 9 lines]
> 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?
Unfortunately I didn't get to see the crank pulley after it had been
removed. While it was in situ, most of it was hidden by the belt, in a very
narrow gap between the engine block and the body of the car. There wasn't
enough space for me to get my arm in to feel down to the bottom of the
engine to reach the crank pulley.
> 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.
When the engine was running, when I first looked after I got the car home,
the pulley appeared to be wobbling side-to-side on its shaft instead of
running true to the shaft as it does now.
Steve B. - 06 May 2008 22:45 GMT
>Ah, so it's acceptible to have a belt where the longitudinal ridges have
>cracks at closely-spaced intervals all the way round the belt? OK. It looked
>as if it was badly perished, but maybe it was still serviceable.
Here's a decent guide with pictures:
http://www.haynes.com/files/product/240.59010sp.pdf
Steve B.
Mortimer - 07 May 2008 07:08 GMT
>>Ah, so it's acceptible to have a belt where the longitudinal ridges have
>>cracks at closely-spaced intervals all the way round the belt? OK. It
[quoted text clipped - 3 lines]
> Here's a decent guide with pictures:
> http://www.haynes.com/files/product/240.59010sp.pdf
Thanks for that. My belt was like the "acceptible" picture at the top right
of the first page, though with even more frequent cracks.
So it looks as if the belt itself was OK and it was a pulley that destroyed
the belt.
HLS - 08 May 2008 13:23 GMT
"Steve B." <none@none.com> wrote in message
> 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.
We had an idler fail on a Buick 3800 application a couple of years ago.
Absolutely quiet until the failure, and of course it ate the belt. Luckily,
wife
and I were only a couple of miles to the next town where we could get it
changed.
Hardest part was trying to exit the motorway and make the turns to get to
the
garage with no power steering.
In this case, the idler was also part of an aluminum casting which served
some
other purpose (dont remember now what) and was not serviceable as a separate
part.
I looked at your Haynes link, and even though it says it is acceptable, I
wouldnt
feel very comfortable going on the road with a belt that looked like that.