Crank Support & Belt ???'s - Fontana/Miner

A question for the guys running screws in NHRA, with Fontana/Miner motors....

Have you found that an RCD front crank hub support is a good thing to have, or just something else to get in the way?

The intended application is high RPM's, high boost, 8mm 1792-224T belt, 74 bottom pulley, 2:1 over, PSI convex flanged idler. Already have the PSI hub & flange kit which we would have to remove to go to the RCD bearing crank support deal.

Any rough rules of thumb for setting slack when cold and checking when warm? Idler is in the middle of the slack side.

 

I havent seen a MBR motor with out a crank support on it, but then
you may get some responses saying it really doesnt help from others,
I believe it does, and it is not just another piece that gets in the way, easy on, easy off. you can change the belt in minutes, I would run it.
Belt should feel about 1/2 to 3/4 slop COLD, do your warm up HOT and it should be about 1/8 to 1/4 play on the drive side.

 

Thanks.

Just hard to give up all of our PSI crank/hub stuff, so nicely in place already .....

 

Just a small comment on this one. We used to run 8mm belts like this, but had some trouble. Gates tech over here then advised to run a tight setup with the belt tensioned (like a guitar string) after we ripped all teeth of the belt. They advised that too low tension would cause the belt to run high on the pulley especially at high speed and small diameter blower pulleys. This may be more of a problem on the 8 mm belts though. In fact they sell a tool that will record the sound the belt produces to check belt tension.
Our problem was solved and a number of people have followed to run tight belts. I'm wondering what general experiences are with this.

 

BELT tension

when i was having belt breakage problems on my BBC, one of the well known blower companies told me i was running my belts too loose, so i tightened them up per their specifications.

First run I broke a crank at the first rod journal in 20 years I had never broken a crank.

I immediately loosened the belts back up, it was too late. 2 runs later I twisted off the snout on another crank. A couple runs later I tore down my 3rd motor that one the front was also cracked.

I was not running crank supports nor have i run them since, that is the only problem with cranks I have ever had. But, 3 cranks in 6 runs leads me to believe the issue was the too tight belts.

 

TWD, do you recall whether you were running HTD or GT2 type belts? That can make a huge difference. Roots or screw, and what engine?

Policypeddler what engine platform, and roots or screw?

Thanks.

 

We use the gt2 belt on a psi screw, on the 526 MBR motor..
it should be tight after the warm up but not so tight
you cant move it a little,.>>>1/8<<<

 

What's your O/D and pulley size. Right now I've got 37/74 for a 2:1. Was wondering about maybe upping the teeth count on both, but keeping the 2:1, for better belt life.....

 

1.92 OD, and I believe top is a 38/9 Ta/fc.

.....5.57@259,.

 

How is your belt life? Are you running RCD's or PSI's pullies? I heard last night that there is a big difference between the two when running the GT2 belt??.....

 

belt

kb olds block
aluminum heads
8-71 kobelco k8 at 70% over

 

I believe they are Psi pulleys,..regaurdless we change the belts
at every 8 runs, 10 at most if slipped by on the paper work.
Just like the rods in a full compition performance level winning car
we change them out before any thing could or would happen.

 

Thanks. Could I bother you for a picture of the front of your all-dressed MBR? whome@look.ca. Just curious what a standard dressed MBR setup looks like. I'm going to have to custom make some stuff in my case because of differences in my front cover.