BB adapter choices/ suggestions

Help Support Rat Rod Bikes:

Joined
Jan 5, 2021
Messages
43
Reaction score
82
Rating - 0%
0   0   0
I know this is a newb question and Ive been clicking around the past few days here and on all the BMX manufactures' sites. What are my choices for converting this 49DX BB over to be able to use a cool CNC'd crank set from company's like Profile/ etc? I understand when doing these conversions for klunkers it takes some trial and error so I have a TruVativ American to Euro BMX Bottom Bracket Adaptor on order as a starting point but are there any press in type options out there? And is chainline going to be a problem? The manufacturers dont all give exact measurments, they just say , "fits all American BB"
BB Measurements are ID 51.67mm / width 65.85mm / and a pic of original 1pc with chain ring for chain line reference. Im gonna use a Bendix 2 speed so I guess I should be shooting for a similar chainline to the original.
49DX BB w:original chnring .JPG
DXBBwidth65.85.JPG
DXBBID51.7.JPG
 
Joined
Jul 10, 2018
Messages
812
Reaction score
2,158
Rating - 100%
2   0   0
Chainline depends on bottom bracket spindle width and cranks mainly. A 125mm BB cartridge type should suffice with a single sprocket crank. Chainline adjustability is limited to the front in cases where the cog is integral to the hub such as the Bendix. Dished coaster cogs available in various depths can be flipped to achieve an ideal chainline.
sturmey-archer-sprocket-cog-for-3-speed-hubs.jpg


Popular sealed YST BB for square taper cranks. The spindle can be moved slightly laterally to one side for a proper chainline.
YST.jpg


Sealed kit for either 19 and 22mm spindle Redline cranks.
redline.jpg

Quite a few options, depends on usage and crank selection. Chainline for single speeds should be straight as possible. Many folks here have done all the above conversions with moderate width tires successfully without too much fuss.

There's a possibility TruVativ type cups may require additional work to fit as in the video. Some BB's have obstacles. Note the manner how the spacers are applied.
 
Last edited:
Joined
Jan 21, 2009
Messages
9,237
Reaction score
9,957
Location
Zambales, Philippines
Rating - 100%
8   0   0
I've swapped the chain wheel from inside to outside the crank to get a better chain line.
DSCI0082.JPG

With the parts you're getting it should work fine. I went el cheapo the first time I did a conversion and it was a big improvement over the original one piece crank.
DSCI0024.JPG
 
Joined
Oct 15, 2008
Messages
1,659
Reaction score
771
Location
The Bayou City
Rating - 0%
0   0   0
I had bad luck with the type of BB adaptor that has three long screws connecting the 2 sides. The bottom bracket tube on my old western flyer contained a lot of welding flash. I tried to grind down the obstructions with a Dremel and big file, but the three screws were still very difficult to line up, it didn’t stay in adjustment very long,
On my Flightliner, I used the cheaper, simpler adaptor that has no screws. It has worked really well. BB bearings stay in adjustment.
 
Joined
Mar 15, 2007
Messages
596
Reaction score
34
Location
Madison, WI
Rating - 100%
7   0   0
I've swapped the chain wheel from inside to outside the crank to get a better chain line.
View attachment 180570
With the parts you're getting it should work fine. I went el cheapo the first time I did a conversion and it was a big improvement over the original one piece crank.
View attachment 180569
got a link where one could get this type conversion, or the non screw one
 

Latest posts

Top