Strong freewheeling crankset

full-throttle · Feb 8, 2013

Most if not all freewheeling cranksets at the moment require an exra wide bottom bracket. Usually square taper. While that's ok for riding on pavement, there's a need for something stronger for off-road use.

Ideally the crankset should have:
1) Splined crank interface
2) Provision for the inboard bearing
3) 73/68mm shell width
4) Low Q-factor

If you come across something that ticks all of the above, please let me know and I'll update this post with a link.

Here's what I came up with
Bottom bracket - Truvativ HammerSmidt AM 73/68mm. Did not come with M15 bolts.
Crank arms - Any ISIS will do. Picked a set of TryAll ISIS 175mm from tartybikes.co.uk
Freewheel - Any 1.37"x24tpi. Picked WI ENO from sickbikes.com
Chainring adapter plate - DIY
Inboard bearing support plate - DIY
Inboard bearing reducer - DIY
Chainrings - TBD
Chainring bolts - extra long or DIY

Now, a small problem. Truvativ BB is not actually ISIS compatible, however the difference is small. Forcing the cranks on might work. This what it looks like after starting to force them

BB compared with 150mm square taper

Crank arms compared

Once the crankset is assembled there should be ~16mm of room left

WI ENO leaves ~10mm for the inboard bearing

BB is 140mm wide with 13~15mm crank engagement.
Axle is 21.2mm dia where the inboard bearing goes, so needs a reducer/spacer. Metric size is 25mm id. Imperial is 7/8".

..to be continued..

Thud · Feb 9, 2013

You sir,
Are a tease....
Been waiting for some one to step up & show if this can be done.

On Greg's giant, I am going the easy way simply machining the sq-taper onto a 20mm spindle.
But I would like Isis cranks as an option.

Please continue :mrgreen:

Miles · Feb 9, 2013

f-t,

You might be lucky but, the problem that boostjuice found was the poor concentricity between the freewheel mount and the axle mount, on most cranks. My solution was to mount the support bearing to the inner part of the freewheel. Having said that, the GNG support bearing is mounted on the axle and appears to be ok.....

spinningmagnets · Feb 9, 2013

edit: a handy chart I found, might help some?
http://img.diytrade.com/cdimg/1040727/12426982/0/1270806925/bicycle_parts_bottom_bracket_parts.jpg

I'm glad you are working on this. I believe the adapter that connects the FW to the BB-shaft can be secured well-enough by two set screws pressing on two dimples that are drilled into the side of the BB-shaft. Just an option I hadn't seen before and thought I try if I ever got to this as a project. Boostjuice used a key/slot...very strong, but not easy for the average guy to do in a garage with simple tools.

Also, there may be some useful ideas in the BB-build by boostjuice (I don't know if this is deecanios BB, or deecanio made a copy of this):

http://endless-sphere.com/forums/viewtopic.php?f=28&t=41547#p612342

wildharemtbkr · Feb 9, 2013

BMX three piece chromoly cranks are the strongest, such as redline flights, http://www.redlinebicycles.com/components/cranks
Or profile racing, http://www.profileracing.com/estore/browse.php?perPage=0&tag=bmx-cranks
Then this adapter allows them to take a freewheel. http://durgendesigns.com/ddfwadapters.htm
Not the lightest setup, but bzhwindtalker proof!

How big is the id of the support bearing that comes with the gng kit? That would solve all the problems.

LightningRods · Feb 9, 2013

full-throttle said:
BB compared with 150mm square taper
View attachment 4

There are two different issues of strength being discussed. The chainwheel is being subjected to unusually heavy loads because of the motor. The support bearing in combination with a heavy duty freewheel (hopefully) solves for that. Another issue of strength is the loading on the cranks from taking jumps and bumps off road. I've bent a few footpegs on dirt bikes.

The spindle extension on the GNG and similar to make room for all of the front freewheel monkeyworks creates a longer lever out past the BB bearing and makes it more likely that the spindle will get bent. The fat diameter of this Truvativ spindle is what is needed for off road.

So if the GNG front freewheel method seems to work let's adapt it to this heavy duty spindle.

LightningRods · Feb 9, 2013

Money no object? http://www.profileracing.com/estore/product.php?productId=401 :twisted:

full-throttle · Feb 9, 2013

Miles said:
f-t,

You might be lucky but, the problem that boostjuice found was the poor concentricity between the freewheel mount and the axle mount, on most cranks. My solution was to mount the support bearing to the inner part of the freewheel. Having said that, the GNG support bearing is mounted on the axle and appears to be ok.....

Didn't think of that..

Would either have to machine the id on the reducer to allow for eccentricity. So instead of 21.2mm make it 22mm. Once assembled the reducer will be friction locked in place by the crank arm. The way you've done it is prob better though. OR use retaining compound (or shims) between the reducer and the support bearing.

I mentioned it earlier - GNG doesn't really solve the problem. The id of the support bearing is 16mm while the BB axle is 15.8mm.

Miles · Feb 9, 2013

full-throttle said:
I mentioned it earlier - GNG doesn't really solve the problem. The id of the support bearing is 16mm while the BB axle is 15.8mm.

Ah, I missed that.... Great solution :mrgreen:

Miles · Feb 9, 2013

20mm axle is about the largest you could use with my system and 25mm ID bearing:

Miles · Feb 9, 2013

Next useful bearing size up is 30mm ID x 7mm (42mm OD)

Edit: Make that 30mm x 47mm x 9mm (6906)

Miles · Feb 9, 2013

Miles said:
Make that 30mm x 47mm x 9mm (6906)

With 6906 bearing and 22mm bore:

Miles · Feb 9, 2013

Another possibility is a 16006 bearing: 30mm x 55mm x 9mm.

flyinmonkie · Feb 9, 2013

Thanks for the pics f-t. Watching with interest. I didn't really like my first through the cranks build, but I want to do a full sus and it seems to be the easiest way so far. It would be nice to have a nice strong crank.

Clay

crossbreak · Feb 9, 2013

spinningmagnets said:
I'm glad you are working on this. I believe the adapter that connects the FW to the BB-shaft can be secured well-enough by two set screws pressing on two dimples that are drilled into the side of the BB-shaft. Just an option I hadn't seen before and thought I try if I ever got to this as a project. Boostjuice used a key/slot...very strong, but not easy for the average guy to do in a garage with simple tools.

Also, there may be some useful ideas in the BB-build by boostjuice (I don't know if this is deecanios BB, or deecanio made a copy of this):

http://endless-sphere.com/forums/viewtopic.php?f=28&t=41547#p612342

This is an extremely dangerous construction! The shaft is too long... too much bending load! Also it will feel horribly flexible

panurge · Feb 10, 2013

full-throttle said:
Now, a small problem. Truvativ BB is not actually ISIS compatible, however the difference is small. Forcing the cranks on might work. This what it looks like after starting to force them

2 questions:

- Howitzer and ISIS are not truly compatible in most cases, I had bad experiences trying Howitzer cranks on isis BB and vice-versa. Mostly on the left side you could need an howitzer crankarm. The Howitzer BB that you have is an hybrid system originally born to fit only An Hammerschmidt crankset, basically an ISIS RH and an Howitzer LH, note that there is also a FR version with a stronger spindle, and, if I well remember, also a slightly wider Q-factor/chainline.

- The ISIS drive side bearings on hammerschmidt BB are not known to be so reliable and strong I say this from direct experience.

I use a 148mm spindle howitzer (non HS) team BB with howitzer cranks to clear the jackshaft+torque limiter of my Recumpence's Drive and get a wide setup but with the strength of a true FR set.

It's not good for a freewheeling crank but I think is perfect for a common jackshaft scheme in a FS bike.
For a Full Susp bike, indeed, the best way should be to have a common jackshaft for both, pedal and motor, concentric to the pivot Point, with a double freewheel System there.

crossbreak · Feb 10, 2013

Sry can't help you with crank issues, I use simple octalink hollow shaft ones and they do great -with one downside:
There is almost no space left for the motor mount, I had to use thin 1.5mm sheets. That's why I'll eventually upgrade to a hollow tech II bottom bracket. With this system you can just add spacers till it fits, perfect for fastening a motor mount sheet. I want to use stiffer 3mm sheet for the motor mount then.

For a Full Susp bike, indeed, the best way should be to have a common jackshaft for both, pedal and motor, concentric to the pivot Point, with a double freewheel System there.

Totally agree. The jackshaft does not have to be concentric to the pivot point. If the chain passes right along it does fine.

full-throttle · Feb 10, 2013

I understand the benefits of a jackshaft, but that's beyond this topic. Freewheeling crankset appeals to anyone using a standard frame.

@ Thud - 20mm BB spindle should be strong. Here's ISIS standard just in case you change your mind about square taper.

panurge said:
2 questions:

- Howitzer and ISIS are not truly compatible in most cases, I had bad experiences trying Howitzer cranks on isis BB and vice-versa. Mostly on the left side you could need an howitzer crankarm. The Howitzer BB that you have is an hybrid system originally born to fit only An Hammerschmidt crankset, basically an ISIS RH and an Howitzer LH, note that there is also a FR version with a stronger spindle, and, if I well remember, also a slightly wider Q-factor/chainline.

- The ISIS drive side bearings on hammerschmidt BB are not known to be so reliable and strong I say this from direct experience.

The two standards are different. ISIS crank arm can be fitted to Hammershmidt/Howitzer by broaching the crank arm, but not the other way around.
Both sides of Hammershmidt/Howitzer spindle are identical.
The drive side bearing is much shallower, but it is also much wider.
I'm aware of the FR option.

spinningmagnets · Feb 10, 2013

Chainring adapter plate - DIY

You can't really call yourself a DIY garage builder if you can't make a disc adapter, but...for those who are in an hurry, Bikemotive makes flanged FWs (like the flanged ENO), and as a result they also decided to provide $41 chainring adapters for 104, 110, and 130-BCD chainrings. Material is 7075-T6 Aluminum at a thickness of 4mm (0.157-inch).

edit: also available at Sick-Bike-Parts and Staton-inc

http://www.ebay.com/sch/bikemotive/m.html?_ipg=50&_sop=12&_rdc=1

Here's one of my early efforts:

Thud · Feb 10, 2013

FT-thanks for that.....more simple than I imagined. (so much for gussing it was too tough to even look up...Dhuooo! :!:

)
going shoping for 22mm id berings now for an indestructable BB :twisted:

full-throttle · Feb 11, 2013

Miles said:
With 6906 bearing and 22mm bore:

6906 looks good

panurge · Feb 11, 2013

full-throttle said:
I understand the benefits of a jackshaft, but that's beyond this topic. Freewheeling crankset appeals to anyone using a standard frame.

Yes sorry, I know it was a bit OT but you mentioned the will for a FS setup so I've said that.

full-throttle said:
The two standards are different. ISIS crank arm can be fitted to Hammershmidt/Howitzer by broaching the crank arm, but not the other way around.
Both sides of Hammershmidt/Howitzer spindle are identical.
The drive side bearing is much shallower, but it is also much wider.
I'm aware of the FR option.

Sorry again, I missed to clearly say that your find/idea with the HS is great and that this BB should be a critical improvement for the application, I would only add my experiences to consider any of the aspects involved. That said ISIS splines are thinner than Howitzers so yes, you could force-broach the female, but as mentioned I had direct bad experiences on that (splines fails fast and you could note alu chips) the howitzer female has rounded splines instead of the flat ones of your ISIS. Another critical question is the spline length (2.5mm shorter on Howitzers) and the room from the arm's spline ends and the inner face (again shorter on howitzers)....though.
Considering the drive side as a custom side and the most important aspect for the topic, I simply suggested the option to use a true Howitzer LH arm like this

(not so different from the Try-all) and eliminate at least the LH probable issues, It's not really elegant but if the arm's weight is similar, for an off-road use, should works...
About the drive bearings, It's obviously anyway a good improvement compared to the standard Chinese Sq.Tapered BBs
Looking forward to your progresses....

skyungjae · Feb 18, 2013

Considering that I belt the left side of my BB spindle last night, I hope you make quick progress on this.

guyavitov · Feb 19, 2013

Im keeping an eye on this thread as well, I have the HW BB and I bought the crank arms that you mention. (ISIS)
Hopefuly they will fit in and ill find a way to make this system work as I already managed to bend very easily two BB's..

flyinmonkie · Feb 20, 2013

f-t, not sure if you have seen this.

http://www.boosty.ch/en/boosty/crank.html

I didn't see a price for the set, but maybe someone can do some further investigation.

Clay

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