BB (crank arm length) upgrade - Huffy Rock It ? Help

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BB (crank arm length) upgrade - Huffy Rock It ? Help

Postby frictionshift » Sun Nov 13, 2016 10:15 am

At first glance it appears to have a standard 1 piece crank, but this isn't the case.
The bottom bracket is a little smaller and has 7 ball cages per side, like on a little kids bike??? :?: instead of the 9 or 10 ball cages that I expected to see. :shock:

So my questions are...
A). Should I convert this to a 3 piece crank set in order to get a longer pedal stroke, since I'm wanting to go from the ~4.5 to 5 inch crank arm to a 5.5 to 6 inch crank arm.
Or...
B). Is their an easier solution? eg. A 1 piece that will fit the BB with the crank arm length that I'm looking for.

I'm looking to keep the cost down and still have the option to play with chain ring sizes.

BB_Rock-It.jpg
Bottom Bracket measurement, Huffy Rock It bike 20"
BB_Rock-It.jpg (42.09 KiB) Viewed 499 times
I'm the old man you see on the bike.
I love my 10 speed, but can't resist taking my 20 inch for a spin.
So I bought this cheap bike to use for donor parts, but find myself trying to build it back up now...
frictionshift
 
Posts: 23
Joined: Sun Oct 02, 2016 10:18 pm

Re: BB (crank arm length) upgrade - Huffy Rock It ? Help

Postby Tomcat65 » Sun Nov 13, 2016 11:20 am

BMX standards are very different than other crank standards. You might get lucky and find a crankset that will work, but some of the unique hardware can be expensive.

And then, kids bikes add a whole other set of challenges. The standards kind of go out the window, and your best bet might be to experiment with one piece crank arms and bearing size combinations just to find a set that works. Donor bikes in good condition and in this size, are hard to find. Ebay sellers who know what they have, can be very helpful with measurements, but many just post sale items and never answer questions or messages.

Finding the proper title for your bb shell size might be the key to finding what you need. Knowing what to ask for is apparently better than knowing specific dimensions when you go to buy a bb. Careful measurement and attention to threads and press fit depth can make this easier if you can find good bb charts.

This was about the best article I could dig up on basic BMX and other bb shell sizing:
http://vectorcycles.weebly.com/tech-articles/5-bottom-bracket-bearing-sizes

A good size/dimension chart:
Image


Let us know what you come up with :)
Tomcat65
 
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Location: Western Kentucky

Re: BB (crank arm length) upgrade - Huffy Rock It ? Help

Postby frictionshift » Sun Nov 13, 2016 11:44 am

Thanks Tomcat65,

I am utterly lost with this one...
I thought that I'd snake the standard crank into the BB and loose pack the bearings, but that's not going to work.
There just isn't enough clearance on this one... Unless.... Unless I pull the cups and figure a way to press them back in with the crank inserted :? .

I'll study the link and see if wrap my brain around it.
At my age charts confuse me, but I'll try.

Thanks for the quick reply.
I'm the old man you see on the bike.
I love my 10 speed, but can't resist taking my 20 inch for a spin.
So I bought this cheap bike to use for donor parts, but find myself trying to build it back up now...
frictionshift
 
Posts: 23
Joined: Sun Oct 02, 2016 10:18 pm

Re: BB (crank arm length) upgrade - Huffy Rock It ? Help

Postby frictionshift » Sun Nov 13, 2016 5:45 pm

I pulled the bearing cups out of the frame and measure in the ballpark of 44.5 - 45 mm OD for the bottom bracket.
Bottom measures 65 mm length without cups.

Funny how I have plenty of shorter cranks that will fit :cry:

This must be somewhat of a common size for little kids bikes since I have several of them about.
It probably has a common name, except I don't know what that common name is.

BB_cup-size_difference.jpg
Top: Standard BB Cup for American 1 pc.
Bottom: Smaller BB cup of discussion.
BB_cup-size_difference.jpg (8.77 KiB) Viewed 491 times


The picture illustrates size difference.
The cup at the top will house a part #66 10x5/16 caged bearing ring.
The cup at the bottom houses a part #?? 7x?/?? caged bearing ring. :?

It might help if these cranks, cups, or at-least the bearing cage had a part number stamped on them.

Would TPI on the 1 pc cranks help much at this point? :?

EDIT - UPDATE:

I now have an ID on the crank:
It is called a Mini Hex or Hex Mini One Piece Crank. Hopefully someone will get some use from that bit of information.
Mine is 4.5 inch (or 115mm) crank arm length... and I believe this is the longest arm length available in Hex Mini one piece crank.

So if I stick with the 1 pc I'm limited to shortening my arm length, no way to lengthen it.

This sort of puts me back at square 1... To find a 3 piece crankset that will fit my bottom bracket.
I'm the old man you see on the bike.
I love my 10 speed, but can't resist taking my 20 inch for a spin.
So I bought this cheap bike to use for donor parts, but find myself trying to build it back up now...
frictionshift
 
Posts: 23
Joined: Sun Oct 02, 2016 10:18 pm

Re: BB (crank arm length) upgrade - Huffy Rock It ? Help

Postby Tomcat65 » Sun Nov 13, 2016 10:23 pm

What I'm reading online, is that a standard one piece crank will work if you can wiggle it into place. An American bb has a much larger diameter shell, and allows a larger crank to ease through. The smaller shell limits the crank at the bend as you install it. of course, but the threads are supposed to be the same 24tpi on standard one piece cranks and the mini hex. The mini hex is just the way the chainring attaches to the crank... So, one piece standard cranks could possibly work with the existing bb bearing set-up..? eh?
Probably not, nothing goes that easily lol
Tomcat65
 
Posts: 1541
Joined: Mon Jun 23, 2014 3:12 pm
Location: Western Kentucky

Re: BB (crank arm length) upgrade - Huffy Rock It ? Help

Postby dddd » Mon Nov 14, 2016 10:25 am

What I would try at this point would be to press in just one cup, then see if the crank and bearings can be fitted into the installed cup.

Then I would check out how the remaining cup and bearings might be fitted to the frame with the crank now in place.

I'm thinking that this would give me the "go, no-go" indication that I was looking for, and hopefully the bearing cones on the bigger crank could still sit at about the right distance apart, within the range of adjustment along the threaded part of the crank, and with the pedals spaced out roughly equal distance from the center of the bottom bracket shell.

Good luck!
dddd
 
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Re: BB (crank arm length) upgrade - Huffy Rock It ? Help

Postby frictionshift » Mon Nov 14, 2016 10:58 am

It has 24 TPI but across a 20mm diameter shaft instead of a 22mm shaft (ballpark numbers).
Just enough difference to prevent anything but the pedals from interchanging. :|

The standard 1 piece crank and it's hardware (might) can be "shaved down" and made to fit the bottom bracket cups, but the bearing size would be tricky.

I'm beginning to understand the concept of "why" when it comes to shimmed 3 piece cranks. :o

If I'm understanding those charts correctly, a MID would be too small diameter and would require shimming :?: .

I "think" that I have an old Pacific with a 3 piece... I'll dig it out and take some measurements if so.
I'm the old man you see on the bike.
I love my 10 speed, but can't resist taking my 20 inch for a spin.
So I bought this cheap bike to use for donor parts, but find myself trying to build it back up now...
frictionshift
 
Posts: 23
Joined: Sun Oct 02, 2016 10:18 pm

Re: BB (crank arm length) upgrade - Huffy Rock It ? Help

Postby frictionshift » Mon Nov 14, 2016 11:13 am

Hi dddd,
I was thinking along the same lines, and an older huffy (outer) cone might will fit to seat the bearings, but I'm pretty sure that the bearings will need changed to another size.
Of course the inner cone will need changing too.. if not "shaved down" to allow it to fit the right cup.

Thanks for the reply.
I am looking into all options (low dollar options anyway).
Appreciate any ideas that come this way.
I'm the old man you see on the bike.
I love my 10 speed, but can't resist taking my 20 inch for a spin.
So I bought this cheap bike to use for donor parts, but find myself trying to build it back up now...
frictionshift
 
Posts: 23
Joined: Sun Oct 02, 2016 10:18 pm

Re: BB (crank arm length) upgrade - Huffy Rock It ? Help

Postby frictionshift » Mon Nov 14, 2016 1:31 pm

It looks as if the Pacific 3 pc might fit (maybe a little small), and after looking at the Pacific I decided to ride down to the local Big Box store.

Mongoose, Kent, and even new Schwinn 3 pc also look close... but I still need to study each individual setup.

Only taking crude measurements, the bottom brackets are close and some of them appear to utilize the same type of adapter that would be required to convert the Rock It.
I'm the old man you see on the bike.
I love my 10 speed, but can't resist taking my 20 inch for a spin.
So I bought this cheap bike to use for donor parts, but find myself trying to build it back up now...
frictionshift
 
Posts: 23
Joined: Sun Oct 02, 2016 10:18 pm

Re: BB (crank arm length) upgrade - Huffy Rock It ? Help

Postby frictionshift » Tue Nov 15, 2016 9:45 pm

So I call Huffy.
My 45mm measurement is wrong.
Huffy says that I have a 47mm (OD) Bottom Bracket.

Anyone know if a PF30 will fit?

I'm reading quite the lot, and it sounds like the PF30 might work, but I might be misreading/misunderstanding something.

Going the PF30 route would be throwing a large hunk of change into a $50.00 bike.
I'm the old man you see on the bike.
I love my 10 speed, but can't resist taking my 20 inch for a spin.
So I bought this cheap bike to use for donor parts, but find myself trying to build it back up now...
frictionshift
 
Posts: 23
Joined: Sun Oct 02, 2016 10:18 pm

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