The car's a 1986 Audi 100 5-cylinder.
Old cambelt has 120 teeth. New cambelt from German & Swedish has 121 teeth. The water pump doesn't have enough movement to tension the belt. It turns out the cambelt supplied was for a 4-cylinder engine, but other than that, would a 121-tooth belt have worked or would it have thrown everything out of synch?
Would have though that if its same length then through out of sync by 1/121 per revolution
The message from Goff Deegle contains these words:
Provided you can get the tension right it'll all stay in step provided it starts off in step at the beginning. The critical section is the bit that runs straight from the camshaft pulley to the crakshaft pulley.
Obviously if the pitch of the teeth is wrong then you're stuffed anyway.
Get a belt with 120 teeth. GSF are great at giving out the wrong parts.
Doh!!! Of course it would have worked. The number of teeth don't affect the synchronisation.
It's actually slightly longer. 1/120 longer, to be exact :-)
The pitch is identical. Presumably if the water pump was offset by another inch or so it would accommodate the extra length. And yet someone in a car parts shop today insisted that the number of teeth was critical, hence my original question.
It would have worked, the number of teeth on the driving wheel and the driven wheel are what counts. You could have any number of teeth in between and it makes no difference.
The message from Goff Deegle contains these words:
They're wrong in terms of timing. Right in terms of whether it'll fit, generally.
Apart from tension adjustment and possible maximum tension compensation on an automatic/hydraulic/spring belt tensioner. In which case the new belt would be so long the tensioner would be near its max travel and MAY have no room to adjust.
Always best to get the RIGHT part when engine timing is concerned.
I bet they were thinking of gears, when it would only be right every 120th (121st?) revolution. Which it would never have got to...
Incidentally that reminds of this which I always thought was really clever.... a very high ratio (100:1 easily) with very very high torque capacity (30% of the teeth are always in contact) in a single small one-gear assembly.
If it helps think about a perfect non-slipping smooth belt. It would stay in sync all the time and yet has no teeth. With a belt all that happens is that the belt moves the distance of the circumference of the driving pulley in one revolution the number of teeth or absence thereof makes no difference. The only reason you have teeth is to stop slip.
We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Goff Deegle saying something like:
That's a new one on me... but thinking about it; if you consider the two vital toothed pulleys - the crank and cam, everything else is irrelevant. Think about how many engines use short or long belts depending on how many other things the belt drives and the crank and cam remain in sync irrespective of the belt length.
So no, the number of teeth isn't important. Just make sure whatever tensioner is there has sufficient adjustment left to work properly.
Like the fuel pump?
Steve
We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "shazzbat" saying something like:
Read what I wrote, again, and see if you can understand it.
Yeah, you're right, no need to bother timing the pump, it won't make any difference. Waste of time the manufacturers bothering with those little dots, maybe they were just for punctuation.
Steve
The 1986 Audi 100 5-cylinder was a diesel?
Tim
We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "shazzbat" saying something like:
No, no, no. For the purposes of this thought experiment, you can disregard the pump, the tensioners, the idlers and everything else but the three main components in the drive train - crank, cam and belt.
Think about it.
The message from "Tim Downie" contains these words:
Well, I've got one. It's 93 actually, but near enough and it's a diesel.
just makes it a bit longer
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