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14th June 2011, 20:07 | #11 | |
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I'm no expert in cam belt, or any other belt technology, but I do know the physics of stretching and elasticity, so I'll offer my view on it.
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With regard to 'slack' belts after a few years sevice, the question is whether they have permanently stretched or has something 'worn' smaller to make them slack? I suspect there's a bit of both, but I doubt the stretch factor is especially significant. Since a belt goes around a fixed circuit, the amount of wear per tooth could be a more important element in slackness than is a true increase in the cord lengths. To illustrate this, I'll ask a simple question I remember from school. A man has a big ball of unstretchable string which he fastens to a stick hammered into the ground. The stick is on the Earth's equator. He walks around the equator unrolling the string so it touches the ground all around the Earth. When he gets back to his stick, he pulls the string tight and ties this end to the stick as well. That's 24,000 miles of tight string. Now here's the relevant part. The man cuts the tightened string with his penknife and inserts 1 yard of extra string into the gap. Naturally, this makes the string around the equator slack, because it's now 24,000 miles plus 1 yard. The man then asks millions of his mates to go around the equator and lift the string up from the ground and hold it above the Earth's surface equally all round. How high will it be off the ground? (Guess if you don't know.) I think exactly the same principle applies to belts. The question is, how much of that 'yard' is stretch and how much is inter-tooth wear? TC Last edited by T-Cut; 14th June 2011 at 20:17.. |
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14th June 2011, 20:11 | #12 | |
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Ford Cortina's....that takes me back, I started off on the old side-valve & overhead-valve engines, Ford Prefects, Anglia's & Morris 1000's (& some earlier stuff) !! Over the years i've worked just about anything & everything (with exceptions of course) I'm now more involved in Diagnostics but it was so much easier in the days of old !!! Sorry about going off-thread everyone.....just re-living old memories. |
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14th June 2011, 20:17 | #13 | |
3disco
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14th June 2011, 20:20 | #14 |
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14th June 2011, 20:21 | #15 |
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14th June 2011, 20:23 | #16 |
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14th June 2011, 20:50 | #17 | |
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14th June 2011, 21:03 | #18 | |
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Circumference being 24,000miles and circumference being 24,000 miles and a yard. Oh and Pi being-----3.141592653589793238462643383279502884 approx. Lol. Colvert. Last edited by COLVERT; 14th June 2011 at 21:14.. |
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15th June 2011, 17:45 | #19 |
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Well since nobody guessed right, the answer is about 1 foot (mathematically it's 1 yard divided by pi). So increasing the 24,000 mile belt by a yard causes it to slacken on the pulley by a foot all round. It doesn't matter what the original length is, the slack is always 1yard/pi. If you translate that to a cam belt and each tooth wears by, say 10 thou, then the belt will get pretty slack compared with its original fitting. The belt hasn't stetched. it's slack because a number of minor wear areas contribute to a significant change in the running circumference/backlash.
TC Last edited by T-Cut; 15th June 2011 at 17:54.. |
16th June 2011, 07:08 | #20 | |
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All Rover group products use Gates HTD belts as O.E. and "stretching" is not one of the criteria, wear to the running surfaces of the belt/pulleys are the factors in play here coupled with incorrect tensioning procedures during installation. Now I may be only an amateur mechanic, however I am a professional engineer, & certainly know a thing or two when it comes to power transmission. Interesting reading. Brian |
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