I am building a couple blower motors and in talking with several people have heard a common issue with marine blown motors. It seems that everyone has an issue with throwing belts. So, my questions is, why is there not a larger belt guide on the pulleys? My set up has maybe a 1/4" on both. Seems to me that if there was a larger/taller one the belt would have to grow much more before slinging off. Just my thoughts....Whats yours?

here's my opinion,,most roots style blowers with the cog set up only have one idler pulley/tensioner..the idler pulley has a step machined in it to keep from throwing the belt on one side,if you were to add another idler pulley on the opposite side of the belt i would think that would help from throwing the belt.watch the belt on one,the side that has no pulley always seems to have a wrinkle in it on deceleration..

The belt must have a set slack, which i think is 3/4" side to side. A tight belt has a greater risk of walking off. I never threw a belt. 195 hrs and counting.


From The Blower Shop website...

How tight should I run my blower belt?
The blower belt adjustment should be done with the motor cold, and have 3/4" deflection in or out on the long side of the belt. This should give you 1 1/2" total deflection. Once the motor is warm this will decrease to roughly 1/4" deflection in or out, or a total deflection of 1/2". Over thightening the belt can cause severe damange to the blower and/or crankshaft

What he said.

I run the belts loose and have never thrown one off.

8mm belt roots blower

Kris Vogt

+1 for never having thrown a belt but I have done my share of explaining why the belts are so loose.

same here never lost a belt on a roots blower and if you run aluminum head they grow more than cast iron .

Now pro chargers on the other hand that junk would kill a belt every run,rib or gilmer

the roots stuff we spin 7000 + and on the party deck we spin 6500 ALL DAY

on my old Scarab at 12psi never had any belt problems.I think the main problems I hear is like the longer belts.like for a PSI or the big Whipple blower, being they run mutable tensioner and idlers

I jumped in without doing my homework... I have gone with a set of prochargers. However, I still hear pros and cons on these setups. I am just trying to do the ounce of prevention thing. I have not had an issue on the dyno (at least with belts) but even with the best simulation it can't apply the forces in the same ways. What has caused the procharger to eat belts? I am still thinking of machining a guide lip to keep the belt inline. It can't hurt, It can't hurt I don't think?.?

The stock mounting plate flexes as the boost goes up, add some braces to hold it solid and you won't loose belts. Adding a guide will probably just wear the edge off and cause the belt to break.

what he said,,also if you have a 6 or 8 rib set up it will go through belts, too small of a blower pulley will cause more slippage which in return will eat belts..i have 2 12 rib set ups on my engines we will see how that works..

ps did you shim the crank pulley properly?