Jockey Journal Forum banner
1 - 13 of 13 Posts

·
Registered
Joined
·
571 Posts
Discussion Starter · #1 ·
Hi All!

Now, I'm pretty new to the world of bikes, and I'm hoping some of the Jedis here can help school a new padawan...

I see a lot of bikes that have big, wide (3"?) primary belt drives. How come the primary has to be that beefy, when a final drive can be about an inch wide, and has to deal with all that engine's torque multiplied by the primary drive ratio X the transmission ratio?

Somehow, I'm thinkin' that if a 1" belt would suffice on the primary, a lot of guys would be running one...

And, how come guys go to belt drives anyway? What's the benefit? Quieter/smoother? I can't believe a guy w/ open pipes and a rigid frame would care how smooth and quiet his primary drive is! Is it to allow a little side-to-side change in where the trans is vs. the engine?

Also, when the primary drive gets changed to belt, then the bike would probably have to have a dry clutch... yeah, no sneaking that past this padawan... how well do the dry clutches work vs. the oil bath clutch? I'd think that the wet clutch should be able to take a lot more slipping, since there's that bath of oil to wick off heat. Don't know that it'd be good for drag racing, but I'd expect it to live longer in stop-n-go street riding. Am I thinkin' right about this?

Anyway, if anybody can answer these questions, then I'll be able to sleep at night! Or at least, find other questions to ponder...

-Bill
 

·
Registered
Joined
·
2,888 Posts
I'll take a shot. When primary belt drives were first introduced most of them were 1 1/2. I started running them on my bikes back in the 70's (enclosed primary) because Harley lubed their primary chains with a total loss oil system. I burned up a couple of primary chains trying to get minimum oil spots under the bike. It took care of the problem. As far as dry clutches go, big twins ran dry clutches well into the 80's, so it's pretty standard stuff.

I think the 3" belts were first run on drag bikes, and then picked up by the street crowd. More of a visual deal than an absolute necessity.

Just one view of things.
Larry T
 

·
Registered
Joined
·
2,698 Posts
I'll take a shot. When primary belt drives were first introduced most of them were 1 1/2. I started running them on my bikes back in the 70's (enclosed primary) because Harley lubed their primary chains with a total loss oil system. I burned up a couple of primary chains trying to get minimum oil spots under the bike. It took care of the problem. As far as dry clutches go, big twins ran dry clutches well into the 80's, so it's pretty standard stuff.

I think the 3" belts were first run on drag bikes, and then picked up by the street crowd. More of a visual deal than an absolute necessity.

Just one view of things.
Larry T
I agree.

There are slim primary belt set ups that fit in the chain covers but people seem to like the open monsters for some reason. I'm not one of them. I watched a guy get his hand spun right through the pulley while his bike was running. The bike didn't miss a beat. No thanks, not for me.
 

·
Registered
Joined
·
1,576 Posts
Harley's from '65 -'84, I think, weren't total loss primary oiling. The primary oil was picked up and ran back to the engine eventually winding up back in the tank.There are still people running these set ups and they work fine but i prefer an open belt.
 
G

·
Larry T nailed it on the head......"SHOW"...

With the narrow belts with 11mm or 14mm teeth and being made from Kelver instead of polyester will take alot of abuse and High HP.....And can be run with primary covers on. (Would be a good idea to vent the cover to avoid heat build-up.) Lessens the chance of critters being where they don't need to be...Not to mention rocks, sticks, fingers and toes..

On the super wide belts ...Kinda need a heavy support plate...even out-board bearings would be a good idea to run if you was going to run hard with doing hole-shots and burn-outs....

As far as why..??
A few reasons come to mind...

(1) Don't need oil for lube...."That's the biggest reason"
No oil leaks if no oil is there....
(2)Less spinning weight.
(3) Dry clutch
(4) Much less maintenance and long life....as long as you don't run a bird or a possum through the dog-gone thing....

100% free webcam site! | Awesome chicks and it is absolutely free! | Watch free live sex cam - easy as 1-2-3
 

·
Registered
Joined
·
2,888 Posts
Harley's from '65 -'84, I think, weren't total loss primary oiling. The primary oil was picked up and ran back to the engine eventually winding up back in the tank.There are still people running these set ups and they work fine but i prefer an open belt.
Your right about the return system, but the bikes still ran the same dry clutches they always ran. They didn't go to a wet clutch until they started running a sealed primary with it's own lubrication. I've converted several bikes over to the sealed primary with aftermarket "wet" clutches. They work fine, but so do the 1 1/2" belts with dry clutches. I've run lot of primary belts over the years, but always in an enclosed primary.
Just "Different strokes for different folks".
Larry T
 

·
Registered
Joined
·
571 Posts
Discussion Starter · #8 ·
Hey guys, thanks for all the replies!

One small question still remains... how come even the 'narrow' belt drive for a primary is as wide as, or wider than, the final drive belt?

Since it's been twenty years since I actually looked at a primary chain, I don't remember the pitch; my recollection is that they were fairly beefy, and were dual row. So, the factory seemed to think some strength was needed there.

Two power pulses at irregular intervals being transferred to the gearbox vs. the same power - albeit gear reduced - having run through a gearbox that tends to dampen a little of the "chop"? If I'm stating my question clearly...

-Bill
 

·
Registered
Joined
·
497 Posts
the pre 65 primary was "total loss" as the oil feed into the primary case then found its way out, hopefully on to the final drive chain, then the ground. in 65 and up with cast alum. primary its scavenged back into the oil system,hence its a recurculating system, not suppost to leak..ha.the same clutches were used in both set ups
 

·
Registered
Joined
·
561 Posts
I like the 8MM 1.5 belt drive over the enclosed chain primary for basically all the above mentioned reasons. Im running the 8mm 1.5 set up on both my 1981 FLH in an enclosed stock primary, and also on my 1949 Pan as an open belt drive. I like to be able to get to things quickly, and (on an open primary) also like being able to see so much more of the left side of the trans, trans plate and its mounts, left side of the motor and all its mounts. In 25 years, Ive never had any close calls or been hurt by the primary. I know its there and what it does when the bike is running. I think its a good upgrade for any vintage bike that gets ridden daily. Same as 12 volt conversion and steel valve seats. Well, nuthin wrong with 6volt. But belt drives and steel valve seats are cool.
Mish
 

·
Registered
Joined
·
3,187 Posts
3" is for nothing but looks and they dont have alot of selection in the low price range for big " motors so you see alot of them from the last decade or so. . I dont know if i missed it anywhere but the OP asked about them being quieter. Hell NO! They are anything but quiet. A nice enclosed primary is very quiet on the other hand. A dry belt is too to illiminate chains and oil and for larger displacement you step up to chain final drives....
 

·
Registered
Joined
·
2,485 Posts
As usual for here, there are a lot of different opinions. Some hate belts, some love them. I am in the love it category. Eliminates the eventual adjustments necessary on the chains, makes working on the clutch a breeze, and replacing the drive sprocket is much easier to access, and inspect. Yes, you can get your body parts caught in them, but I have been running belts for over 30 years, and have never gotten any body parts caught, or even my pants leg. I have around 200 k on my 73 shovel, and it has been belt drive since 82. Some say it is for looks, I say it is easier to work on, and does the same thing as a chain.
 
1 - 13 of 13 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top