ok ive asked everyone I know made a lot of phone calls and im stumped
on my chopper im running a ultima belt drive with a 1.250 offset if I ride it hard within 200 miles im replacing my front pulley insert. it is ripping the splines out off the insert here is what ive checked and tried
pulley alignment, splines on crank are good not being hurt, crank has .0016 of run out, nut is not bottomed out on crank. red Loctite on splines and nut torqued to 120 pounds new belt and front pulley.
im on my 4th insert does anyone have an idea of what could be causing this to happen so fast
I know that all belt drives share this problem but it usually lasts 10 to 15 thousand miles not 200

 

D, assuming it's an open belt. Do you have a support plate connecting engine and trans?

Also since I'm not very familiar with your particular belt drive. Does it have some sort of tensioner for the belt?

Not insulting your intelligent's in any way, but could you have to much tension on the belt allowing too much load on the pulley? Also how does clutch hub bearing feel? Short life on the clutch hub bearing could be another sign of one or another related cause.

Not being familiar with the particular belt drive these are just possibilities off the top of my head.

 

i dont think i can be of much help BUT the belt drives that are being made in *****land the inside metal insert is soft and not hardened steel -- if it is all aluminum you take the new one and have it hard anodized it would hold up a lot better

in my shop we only build period correct choppers - bobbers and when we belt them its a 11 MM and the trans adjusts the tenshion, the centers of those pulleys are american made and i never replaced one --NOW they also do not have the power you have nor are driven as fast as you drive < the rotation mass is less as it is smaller so that does not become an issue -- i would make it 250 not 120 if we did it - d i think it starts to walk back and forth as it is not tight enough - if it lasts 6 more months and does it again than 350 - i think its too loose

 

How much run out on the clutch hub ??
John

 

yes there is a support plate and there is no tensioner. the belt just slides on
just checked the tension belt moves .250 with ten pounds. clutch bearing is tight no wobble at all.

 

I wanted to use the old school open belt but the frame was wrong for it the transmission plate is part of the frame. are you sure the crank can handle that much load on the nut


I think I understand what your saying as the pulley starts to rock on the splines its loosening the nut and when the nut gets loose enough it shreds the splines on the insert is that right? when I put the new one on today I noticed a small amount of play on the splines like 2 thousandth

 

I never checked that I do know there's 0 on the mainshaft ill check it tomorrow im done for the day

 

I would quit putting red loctite on the splines and grease them instead.

After all that is what "splines" do, allow for axial movement(to relieve stress). Think of the splines between the drive shaft and transmission output shaft of an automobile or even a manual clutch.

But, in reality I don't know jack **** about belt drives.

 

something is not right // if the new pulley is already moving it will shread it in no time

i think you need to measure the splines and the hub slots and see whats up guessing on .002 is not going to cut it BUT go and try this

take the hub back off and go to an indy you know and get a Brand new sprocket shaft slide the two together and see if its the same thing LOOSE if so your belt drive is junk and you keep buying more junk when you replace broken stuff

 

im starting to think this part is just junk I have four cranks one is new they all measure the same as the one in the chopper. except the new one is .0015 smaller I thought s&s would have been tighter I don't have any new hubs so I checked the used ones laying around they were all within .0005 of the ultima insert.


when I checked the slop on the splines I did it with a dial indicator on the pulley teeth. so if my math is right the .002 I was getting was closer to .0006 at the splines.
so this is what im thinking you might be right with the hardening. I have a heat treatment place just down the road im going to take one of the old ones and the insert from this old primo belt drive I have and see how hard both of them are the primo has a lot of miles on it and it still looks good