Bottom Bracket Question

[ghsmith54]

I'm building up a new (old) frame and am a bit puzzled. The shell width is 70mm (typical for Italian BB's) but the diameter is 1.37 and the drive side appears to be left hand threads.

I thought it generally went:

Italian:

Shell width 70 mm
Diameter 36 mm
Drive size threading: right hand

BSC:

Shell width 68 mm
Diameter 1.37
Drive size threading: left hand

I'm confused (which is pretty much normal). Is there such a thing as a 70mm BSC bottom bracket (Shimano Octalink)?

Thanks for any replies, especially for correct ones!

Greg

 

[hd reynolds]

I'm building up a new (old) frame and am a bit puzzled. The shell width is 70mm (typical for Italian BB's) but the diameter is 1.37 and the drive side appears to be left hand threads.

I thought it generally went:

Italian:

Shell width 70 mm
Diameter 36 mm
Drive size threading: right hand

BSC:

Shell width 68 mm
Diameter 1.37
Drive size threading: left hand

I'm confused (which is pretty much normal). Is there such a thing as a 70mm BSC bottom bracket (Shimano Octalink)?

Thanks for any replies, especially for correct ones!

Greg

None. Standard shell width in mm are as follows:
- 68 for standard ISO/British
- 70 for Italian
- 73 for oversized ISO/British.

 

[hd reynolds]

Cosequently thread widths follow:

1.37'' (approx. 34.8mm) 24tpi - 68 for standard ISO/British
68mm 24tpi - 70 for Italian
1.375'' (approx 35mm) - 73 for oversized ISO/British

 

[fish156]

I'm building up a new (old) frame and am a bit puzzled. The shell width is 70mm (typical for Italian BB's) but the diameter is 1.37 and the drive side appears to be left hand threads.

I thought it generally went:

Italian:

Shell width 70 mm
Diameter 36 mm
Drive size threading: right hand

BSC:

Shell width 68 mm
Diameter 1.37
Drive size threading: left hand

I'm confused (which is pretty much normal). Is there such a thing as a 70mm BSC bottom bracket (Shimano Octalink)?

Thanks for any replies, especially for correct ones!

Greg

Is your bike an old Raleigh, by any chance?
There were some that were 1 3/8 x 26tpi, 71mm. So, 3/8=.375
If you are off 1mm on your width and .005 on the diameter, this could be it.
Sorry, I'm not trying to pick on your measurements, but this is pretty close to what you are looking for.
The dead giveaway would be the thread pitch. The difference between 24 and 26 tpi is very easy to see with a thread pitch gauge.

for reference, see this page and scroll down to "Bottom Bracket Threading":
http://sheldonbrown.com/bbsize.html

Good luck!

 

[ghsmith54]

Is your bike an old Raleigh, by any chance?
There were some that were 1 3/8 x 26tpi, 71mm. So, 3/8=.375
If you are off 1mm on your width and .005 on the diameter, this could be it.
Sorry, I'm not trying to pick on your measurements, but this is pretty close to what you are looking for.
The dead giveaway would be the thread pitch. The difference between 24 and 26 tpi is very easy to see with a thread pitch gauge.

for reference, see this page and scroll down to "Bottom Bracket Threading":
http://sheldonbrown.com/bbsize.html

Good luck!

Thanks for the reply but no, it's not a raleigh. The bike is a never been built up '90 Landshark. It turns out that it does indeed have left hand threads on the drive side (to summarize: 70mm, 1.37" diameter, left hand drive side threading) and there is no bottom bracket for it. As I recall, "back in the day" it was possible to assemble such a thing but no more. I spoke to Mr Landshark (John Slawta) who at first said "if it's my bike, it's not a 70mm". When I gave him the serial # off of the bike and assured him that although I'm not the swiftest greyhound in the kennel, I do know how to operate a set of calipers and that it was indeed 70mm he said "oops" and admitted that although he specs the shell at 68mm from his suppliers, they must have sent him a 70mm and he threaded it "as usual" with BSC threads.

At any rate, the fix was (relatively) simple. I had 1mm milled off both sides of the shell and now am using a standard 68mm BSC bottom bracket.

Greg