I didn’t think that selecting the right drivebelt would be a problem. On my engine there is no AC compressor and no power steering so it was obvious that the standard belt for the engine wasn’t going to fit. But knowing what I know now would have made the process much easier. Avoid places like Halfords as their part-codes don’t make any sense and that’s the secret to what you need.
On a belt bought from the likes of Partco the stock code gives you the information you need. In the case of the belt I needed for the 1.7L Puma engine it was GMV61175. This code is very close to the code used by the company called Gates. The most important part is the last 4 digits which is the inside belt length in mm, in this case 1175mm, this is all the information you need.
First of all you will need to determine the length of belt that you will need. To do this you will need to use a piece of thin wire. Don’t use string as it can stretch and may give you a false length reading. On modern engines the drivebelt tension is set by a automatic tensioner to compensate for wear, whereas on older engines is set by moving the alternator. To get the right length measurement you will need to set the tensioner or alternator to its upper maximum setting this is sometimes indicated on the tensioner like on the Puma engine. Then run the wire around the pulleys in the way that you want the belt to run and making sure that there is no slack and then mark the point at which the wires pass side by side with a marker. From this you will be able to measure the length of the belt you will need. In my case this measurement was 1150mm.
Don’t go out and buy a belt that has the measurement 1150 on the last 4 digits as it won’t fit. Each pulley has a flange and even with the tensioner fully off you won’t be able to get the belt over the pulleys. You will need to buy a belt slightly longer. I found purely by trial and error that it needs to be at least 25mm to 35mm longer but no greater as the belt will be too long. That is the reason the measurement around the belt was taken at it’s upper maximum setting.
Once you have your ideal length you need to find a belt that matches that. Below is a guide to how the Gates part code works.
Thanks to my Dad for his help on this one.