huge bottom pulley

My 11mm belt/pulley combo requires a HUGE 64 tooth bottom pulley with flat back. I see signs of it flexing/ rubbing the fuel pump extension and the crank triggers behind it.
I tried to get someone to build a custom stronger pulley but it was over 500.00.
I'm sure a center flange pulley with crank support geardrive would help but I have no funds to make the swap and my current setup has lived for 12 runs.
I know in the early days of the screw lots of people ran huge lower pullies. Did they live.?

Thanks
Mike

 

I run a 70 pulley on the bottom with a 6 inch pump extension. I did have to remove about an 1/8" off the bottom of the pump extension. Get a RCD hub and a 3/8 Leahy crank trigger pickup setup and you will be fine.

 

I have an Rcd titanium hub and 2 leahy triggers. The first thing I noticed was the triggers touching the back of the pulley like the thrust was hurt on the crank. I cut .030 off the back of the pulley then .060. Then I noticed the pulley touching the fuel pump extension with .050 clearance sitting still. Something is moving around a lot and the huge pulley with a small bolt pattern in the center looks weak to me. If the crank is flexing that much I guess we'll see how long until it cracks.front main bearing looks fine.

 

pulley flex

Psi used to make what they called a pulley clamp, an aluminum piece that bolt to the pulley and the crank with a long 3/4" bolt. Stiffens the flange area of large O/D pulleys. I ran one on out TAFC at 125 % over, quit having those problems with flex

 

Clamp pic

heres about as good as I have for pics of the clamp he described. http://s918.photobucket.com/user/nitrobandit1/media/10_zps25c3c33f.jpg.html

 

Do you see any signs that the hub is wobbling and moving around on the crank? Do you see any signs of the pulley wobbling on the hub or flexing around the bolts? Do you ever find the pulley bolts or the main center hub bolt loose? Is this a new problem or something that you have been chasing for awhile? If new, what was changed at that time? Have you had the hub on & off too many times and now it is worn?

If the pulley itself is flexing, or if the hub is moving, then the lower pulley clamp will not help and you'll have to get a stiffer pulley. If the pulley is moving on the hub, then the lower pulley clamp may help. I don't know if PSI (or others) have this in 11mm but the PSI 70-74 8mm screw pulleys are flat rear backed with a web that angles out to meet the middle center line of the pulley for added strength. That keeps your spacing correct, but still gives you the effect of a center web pulley.

I'll see if I can dig up some images.

 

Cutting .090 off the back of the pulley as you said you have, certainly isn't going to help make it stiffer ?????

 

Some front covers have a built in roller bearing "crank support" but I like the traditional crank support that supports the other side of the pulley, especially with how tight we run our belt. Here is a link to load dispersing crank hub deal.

http://www.rbssuperchargers.com/Products.cfm?pn=2300-0039&pID=7449

 

Thanks rb084, you saved me from having to figure out the uploading pictures thing.

If you had a clean sheet of paper available for a new engine program, do you have any thoughts one way or the other about: 1)the traditional outboard crank support plate with fabricated stand-offs and bearings, or 2)the AJ style crank support bearing approach that they nestle in behind the pulley with no forward plate and stand-offs?

Designing a custom deal right now and would be open to ideas one way or the other.

 

pulley

Lots of good ideas.
Everything is staying tight with a little metal transfer where the pully sits on the hub. I haven't removed the hub but I suppose I should.
The psi clamp is a decent looking deal. It ties more stuff together. I think i'll build one extra big diameter to cover more of the pulley face. I might even add an additional bolt circle to tie the two together.
I removed .060 total off the back only at the very OD where the triggers are. Still not ideal.
I have a psi design 8mm pulley and it's nice. I tried to get one made in 11mm and it's 500.00.

I think the rcd bearing support timing cover takes care of everything with the center flange pulley.
Nobody wants the old school front crank support due to weight and constant belt replacements.

 

We run an 11mm belt also but we don't replace it very often as there is no need to, they are tough as nails, just make sure you get the belt with the 'PS' in the belt number. As for the removing the outboard support, four bolts and the deal slides right off with minimal resistance if we do have to remove the belt for any reason. I'd rather have a little extra weight and piece of mind than a broken crank. Did you have any of these issues Chevrolet?

 

pulley

We've run both types of 11mm belts and never broken one with over 50 hits with screw...and they were used to begin with.
The chevy had a lot smaller lower pulley due to the tall manifold/deck ht. 125% used the smallest top made.
I built a massive crank support for the chevy that seemed to work but at this point I think its pulley/hub flex more than the end of the crank flexing.
I've spent so much time and money getting the car light, i'll eat the front support geardrive cost before I build and run another heavy front crank support.

 

pully

i use the orange juicer (pully support) on my std front timing cover
i dont use it on my rcd crank support center flange set up
but i do use 8mm belts with 69 lower pully