I was wondering if anybody had any info on the correct way to calculate belt length. In the past when I have swapped engines I kept the stock distance to use the stock belt. Now with my RPM Gearbox it's a whole new setup. I had planned on using the belt from the sled my Engine came from, but that distance was way too tight to be functional. So before I spend a bunch of money ordering a bunch of belts to try, I wanted to see what my options were for doing this the correct way. There must be a formula that will get me exactly what I need.

I did a quick search and didnt find anything, we will see what comes up under this thread, maybe it's been discussed before. I created a seperate thread as I thought it would be useful information to have on record.

I have never had a reason to determine different belt lengths, so this is purely off the cuff,but could’nt you measure with a piece of rope or something, just to get in the ball park? Just throwing out suggestions. Good luck!

I had to think about this for a second because I am getting old and forgetting my millwright stuff.
You take your center to center length multiply that number by 2 -- write it down on paper.
Then find the circumfrence of the primary clutch (PI x D) -- write it down on the paper.
This should be your belt length.
The clutches shift at a 1 to 1 ratio no ?? So this should be correct.
The other factor to consider is the belt deflection. You need some slack or it will be driving the driven all the time. If I were to guess then I would add half inch at least.

On the gearbox drive units I work on in factories it is a bit different than our variable clutch set up we got here on our oddys.
On a drive unit you measure c to c times two and then take half of the circumference of each pulley and add. That's the belt length. Now you use the take up to tighten it.

Edit: I just went out to the shop and it comes in real close if you don't add the extra half inch for the belt deflection I talked about above. The calculation seems to give me the belt deflection. I would have to take a machine apart to get more accurate but I don't want to do that. Just do the above calculations and I think your good. Otherwise we have to wait for a propeller head.

Edit: HELLO adnoh !!!!