I've looked at basically every site on the internet and searched this one for serpentine and can't find out what size belt to get. On Rockauto, Advanceautoparts, and autozone, they all list either a 54.75" belt or a 41.5" belt and they don't list the differences except one says WP (water pump?) and one says A/C. Now I think all Coopers S's have A/C AND a water pump, correct? Would suck if they didn't

Could someone help me since i am going to place an order online and would like to order a belt as well, but won't be able to return it if I order the wrong one ( I need to order from an online site for other parts that I can't get locally).

 

You could check with any one of our vendors here, or NAPA.

The size of the belt is determined by what size supercharger pulley you have....basically the smaller the pulley you are using, the smaller the belt is to prevent slippage.

 

I'm Stock :P

 

For a R53 S it's a "545" (54.75) - unless you have a reduction pulley, then use a "535" (the number on my Gates belt are "K060535" over "6PK1364"). These are available at almost any parts store if you don't want to order (or try two diff sizes)...
The water pump is on the back of the supercharger...
The other size must be for R50 or R56 (idk)...

*trivia: the "535" application on a Dayco belt is listed for a 1.9L Ford ...

 

Since your doing the belt.....maybe a good time to upgrade that pulley

 

....and add a tensioner stop!

 

Big +1 on the tensioner stop..cheap insurance good idea BS.

 

Just picked up a Gates belt for my R53, turns out they gave me the WRONG one (K060547 - 55.25" belt) so I took it back, then the sales person had the *alls to say " well thats what our computer shows, so you must have the wrong information as to the correct size" This is just after I get off the phone w/ the Mini parts guy who tells me" you need a 54.75 inch belt". So, I went to PepBoys and the sales guy looks up an R53 on his computer, then turns to me and says that my car takes a 34" belt....

Lastly, I had to go to Autozone who had the right belt (Duralast - 550K6) Three hours later, I have the right belt.

This was a good lesson to NEVER trust a sales person!!!!!