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+--- Thread: Question for math boffs - serp belt size (/showthread.php?tid=8397)
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Question for math boffs - serp belt size - jimxms - 15-07-2019
So I'm going from a 2.55" pulley on my supercharger to a 2.25" pulley. The serpentine belt that currently fits great is a 6PK2515 (2515mm) belt.
My basic 'year one' maths tells me that the pulley is 0.30" smaller in diameter, but as the belt only makes contact with half of the pulley, I only need to account for 0.15" difference which is 3.8mm.
Now, the question is if I deduct 3.8mm from the 2151mm belt will that be correct, or do i really need to deduct 7.6mm from the belt length to account for the fact that I need to reduce the circumference by 3.8mm?
Or am I speaking utter twoddle. Someone help!!
Question for math boffs - serp belt size - Dark Samurai - 15-07-2019
You'll have to keep the 7.6mm belt I think, but what do I know, I only got a B in maths yesterday
Question for math boffs - serp belt size - jimxms - 15-07-2019
Dark Samurai You'll have to keep the 7.6mm belt I think, but what do I know, I only got a B in maths yesterday
7.6mm belt is a bit small
Back to school for you.
Question for math boffs - serp belt size - Dark Samurai - 15-07-2019
The one that's the 7.6mm you're talking about, not 3.8!!!!!!!!!!!!!!!!!!!!!!!!
Question for math boffs - serp belt size - sprinter2012 - 15-07-2019
Don't take this as gospel, but it makes sense in my head...
You need to work out the circumference of the part of the pulley that the belt will sit on for the old and new pulleys...
Old Pulley Circumference = a
New Pulley Circumference = b
Then half them both, so now you have a/2 and b/2
Then do (a/2)-(b/2) which will tell you how much shorter the belt needs to be :thumbup:
Question for math boffs - serp belt size - jimxms - 15-07-2019
So, if the belt makes contact with exactly half of the pulley
a = 64mm (2.55")
b = 57mm (2.25")
a/2 = 32mm
b/2 = 28.5mm
32-28.5 = 3.5mm
That right?
If so, the current belt might work ok if it only needs to be 3.5mm shorter.
Question for math boffs - serp belt size - sprinter2012 - 15-07-2019
Looks right to me, specially as the figure you had before was 3.8 so it's all in the right area :biggrin:
EDIT: And as you rightly said that's assuming the belt is in contact with exactly half the pulley
Question for math boffs - serp belt size - D.F!ANT - 17-07-2019
:confused1: didn't/couldn't the suppliers provide you with the necessary length?
if it were me, i'd cut the old belt, fit it and measure the gap to get a rough idea, (maybe with a strange assortment of clamps to keep it taught), And then compare that to the Math!
Question for math boffs - serp belt size - Mikey - 19-07-2019
or to save the old belt use a bit of string/shoelace/washing line, anything long enough
Question for math boffs - serp belt size - jimxms - 19-07-2019
I think the problem with using string/cutting belt is that its going to be quite hard to get the size right when you're going to be fighting with the belt tensioner.
I may just have to buy a few belts _around_ the size I think I'll need and see if I can get the shop I buy them from to agree to me returning the ones that I don't use.