Belt drive Rules of thumb??

[mike_starling]

OK Guys,

I have finally gotten to redoing the front end equipment for my engine. The engine is built on a 4 bolt race block and has an external oil pump ... so I have to have two layers of belts. Three makes the engine too long.


I got a short Ford Hot Rod water pump and that will also help the length of the front end. So far it appears that I can get everything within the overall length of the air conditioning compressor.

The single additional belt layer requires using a serpentine set up. To make this work I'll have to have idlers to guide the belt around the water pump pulley to get sufficient bite on the pulley. Have made the idlers and a new water pump pulley. Have made a mounting plate that successfully drops over all of the appropriate bolts. (Don't even have any "oval" holes yet.)

Are there any rules of thumb regarding the path of the belt ... that is the layout of the idlers?


Thanks,

[Lynn]

Mike,

Working from memory, I think the absolute minimum contact patch between the flat serpentine belt and the pulley is like 90º, with around 180º being optimal. The width of the belt would of course be a factor, but I think this was with a standard 5-6 rib belt. I think my belt has around 150º of contact and seems to be working fine with my 4 rib belt.

You might want to take a look at March's website as I seem to recall some info there about setting up pulley systems. This may very well be where the notion of the 90º minimum came from, but I set that stuff up so long ago that I am not 100% about it.

Regards,
Lynn