BMX freewheels: Cheap, cheaper, cheapest.

[TylerDurden]

A look inside three common single-cog freewheels. These are large images so you can get a good look.

Two of these freewheels might be used on an ebike, for a primary drive at the hub, stacked at the hub for dual drive, or as part of a BB setup. Can you guess which one wouldn't?

Cheap = Shimano mx30 (~$15)
Cheaper=Long Yih (~$5)
Cheapest = Leader (~$2)

The Shimano was removed without using heat, the other two needed persuasion using "the blue wrench"; hence the discoloration and cooked grease.



Inside, the Leader has wire substituted for many bearings.



The pawls in the Shimano move silently and precisely, the Long clicks, the Leader clicks loudly and the pawls wobble.

View attachment 3

The Shimano springs are thick and surround the hub. The Long Yih springs are thin and fit in a groove in the hub. The Leader springs are smashed and barely get the pawls engaged.



The Shimano back is well machined and flush. The Long reveals that the hub is made from two pieces pressed together. The Leader shows the holes for the pawls' pins.



The Shimano pawls both engage at the same time due to an even number of CPs (contact points = 20). The other two have 21 CPs, so only one pawl is engaged at a time. All of the force of a cyclist or motor is bearing on one pawl.



In addition to the pix, it should be noted:

The Leader is very loud and has significant play or slop in its rotation. The Long Yih has less. The Shimano has no sound and no slop.

There are more expensive freewheels available: "trials" freewheels can cost quite a bit, actually. I'm not going to rip one open, unless sombody sends me one.

 

[kbarrett]

I have a Shimano freewheel on my evil smoker that I singulated.

Absolutely no complaints about it.

It just works.

 

[TylerDurden]

It would also be fairly easy to convert the Shimano to a four-pawl, by using a rotary-tool and two spare pawls.

8)

 

[gogo]

stacked at the hub for dual drive,

Could you really get two of these threaded onto a rear hub?

 

[Miles]

Good idea for a topic, Tyler.

The Shimano looks pretty good.

The ENO is the one I'd recommend for a front freewheel. The Tensile would be a cheaper option.

I'll take some pics of mine, next time I open it. Until then: http://www.tartybikes.co.uk/category.php?id=65

 

[Toorbough ULL-Zeveigh]

wow, quite the education & very revealing.
thanx for the heads up, I know this will save me frustration at some future point, forewarned is forearmed etc.
I can't envision a good reason for the odd number of contact points.
The downside is obvious but there must be some benefit to the trade-off, typically it's to lower cost but I just don't see how.
Too problematic getting simultaneous engagement with poor tolerances? :?
Rhetorical question but any speculation is welcome.
you working on putting together a Hallekela Special or sumpthin?

 

[TylerDurden]

I can't envision a good reason for the odd number of contact points.
The downside is obvious but there must be some benefit to the trade-off, typically it's to lower cost but I just don't see how.
Too problematic getting simultaneous engagement with poor tolerances? :?
Rhetorical question but any speculation is welcome.

Right on all points, I rekon:

20 CPs provide engagement every 18 degrees of rotation. That's a fair bit of swing before contact, so the shock of contact could be more than a dog can take.
Since the manufacturing slop-factor could allow for one dog to catch first, it would take the whole hit of engagement anyway.
Adding the odd CP reduces the amount of rotation to 9 degrees before contact: half of the momentum and reduced shock-load.
Changing the casting for the ring could be the easiest, cheapest solution.

Pure WAGging here, but hay... I'm fresh outta SLA jokes.

 

[Toorbough ULL-Zeveigh]

that makes a lotta ¢.
I didn't connect how an odd number would cut the step in half till you pointed it out.

 

[docnjoj]

ThanksTyler! My suspicions are that my cheep Dicta freewheel for my left side hub to motor connection is like your "poor" one. Oddly enough, the left side reverse thread freewheel on the original CX24 (Currie) hub is virtually silent! Go figure. Updates and pictures on the 3speed hub thread soon!
otherDoc

 

[Drunkskunk]

Nice. I wounder how hard it would be to add 2 more sets of powls to the Shimano. Give it 6 degrees of engagement. back in my stunbike days, that was sonething I hated, my bike took too much rotation to engage, and made some tricks imposable.

 

[TylerDurden]

@gogo:

Git yerself a BB cup the same thread as the hub (24tpi):



Thread on the first FW:


Thread in the BB cup:


Spin on the second FW (can be a multi-gear too.):



A longer axle might be req'd to add the extra FW.

For builders considering driving the rear wheel directly with a motor and chain, this is a way to keep your pedals and motor isolated. For motors without gear reduction, a large sprocket could be grafted to the inner FW.

 

[Miles]

Nice. I wounder how hard it would be to add 2 more sets of powls to the Shimano. Give it 6 degrees of engagement. back in my stunbike days, that was sonething I hated, my bike took too much rotation to engage, and made some tricks imposable.

Some of the trials freewheels have 72 points engagement (5 degrees).

 

[docnjoj]

That is truly clever, Tyler! I wish I could do it on the left side!!
otherDoc
edit: Actually it may be possible. Dont other side BBs have reverse threads! Then I just have to machine 1 set of reverse threads on the left side of the SA or Shimano 3 speed!!!
otherDoc

 

[TylerDurden]

That is truly clever, Tyler! I wish I could do it on the left side!!
otherDoc
edit: Actually it may be possible. Dont other side BBs have reverse threads! Then I just have to machine 1 set of reverse threads on the left side of the SA or Shimano 3 speed!!!

You want two FWs on the left?

 

[docnjoj]

Nah! I just realized I cant use this great idea!
otherDoc

 

[TylerDurden]

Nah! I just realized I cant use this great idea!
otherDoc

Sure you can... on your next bike/setup.

 

[ebike11]

@gogo:

Git yerself a BB cup the same thread as the hub (24tpi):
View attachment 5
View attachment 4

Thread on the first FW:
View attachment 3

Thread in the BB cup:
View attachment 2

Spin on the second FW (can be a multi-gear too.):
View attachment 1


A longer axle might be req'd to add the extra FW.

For builders considering driving the rear wheel directly with a motor and chain, this is a way to keep your pedals and motor isolated. For motors without gear reduction, a large sprocket could be grafted to the inner FW.

so helpful. thx