Serp belt with underdrive pulleys

[prpleranger]

Has anyone been able to use stock belt with underdrives? i am having an issue and was wondering how much shorter the belt actually needs to be inorder to get the automatic tensioner to work right

[MalcolmV8]

I've always had to go to a smaller belt. One thing I've read is run a piece of string through all the pulleys and then measure it. Good luck holding the tensioner in the correct position while measuring though. I think I checked how much slop was in my stock belt and then guestimated the new size. Hopefully you have a cool parts counter guy at your local parts store that will let you swap it out if you guess wrong.

[usmcrp1044]

Yeah, do the rope trick.

I took a super long belt, and put a pair of vice grips on it and went down to the parts store. The chick that works there told me a rope was the easiest for them to get the measurements from.

[prpleranger]

Thanks for the info i think im going to get a few belts im thinking maybe 1/4 to 1/2" shorter i dont think its as much as an inch.
This whole project has been a nightmare have had problems with piston bottoms hitting crank then note to everyone if you buy a profesional products balancer you will more than likely need a pulley spacer and none of the timing marks are right on it find #1 tdc and make your own 0 deg mark and pretend the 3 other sets of marks arent there

[94stranger]

certain brands of under drives require a s maller belt, the set I got can use a stock one

[prpleranger]

i got it working had to drop 1/2" off stock belt and it works perfectly