Bicycle Mechanics - BB cartridges, spindle widths - replacing crankset (MTB->road double)

Latest upgrade didn't work out as planned. Rear cassette and derailleur upgrade went fine.

Problem: took the MTB front-double-crankset off (FSA Alphadrive, 44/32) and slid the salvaged road double on (from a 1985 Norco FWIW). CLANK! The rings hit the chainstays!

Bit of comparison - big difference in clearance. The FSA crank-arms have a mild "S-curve" that puts the outer part of the arms way out. They also have sort of a "bulge" where they mate with the BB spindle.

The road crankarms are straight, with no bulge, putting them probably 1/2 to a full inch closer to the frame.

:(

Is this a case of needing a new bottom bracket?

On that note: the BB has splines which I've never dealt with and don't have a tool for.
Does this imply I'm dealing with a cartridge BB, as suggested by several websites?

Bummed. Can't afford a new cartridge. I don't think I'll be finding one of those in the trash anytime soon either.

:(

:(

Latest upgrade didn't work out as planned. Rear cassette and derailleur upgrade went fine.

Problem: took the MTB front-double-crankset off (FSA Alphadrive, 44/32) and slid the salvaged road double on (from a 1985 Norco FWIW). CLANK! The rings hit the chainstays!

Bit of comparison - big difference in clearance. The FSA crank-arms have a mild "S-curve" that puts the outer part of the arms way out. They also have sort of a "bulge" where they mate with the BB spindle.

The road crankarms are straight, with no bulge, putting them probably 1/2 to a full inch closer to the frame.

:(

Is this a case of needing a new bottom bracket?

On that note: the BB has splines which I've never dealt with and don't have a tool for.
Does this imply I'm dealing with a cartridge BB, as suggested by several websites?

Bummed. Can't afford a new cartridge. I don't think I'll be finding one of those in the trash anytime soon either.

:(

:(Cranks have sepcific spindle length requirements that can vary significantly from crank to crank. Sometimes you get lucky,most of the time you don't. Splined BB sounds like a cartridge type.

Pretty sure it is a cartridge now.

Looked down the seat tube and there's a small hole drilled into the BB tube (whatever you call that) where you can see a silver sleeve with writing on it inside the BB, implying a cartridge.

FWIW, the width of the current spindle appears to be ~109mm.

On the bike I took the new ringset off, the spindle is ~123mm (not including the threading protruding beyond the tapered spindle)

Does it matter if a spindle has protruding threads versus a tapped thread into the tapered shaft? (other than "one uses a nut, the other a bolt" to hold the cranks on...)

Thanks for the input!
Chris

Pretty sure it is a cartridge now.

Looked down the seat tube and there's a small hole drilled into the BB tube (whatever you call that) where you can see a silver sleeve with writing on it inside the BB, implying a cartridge.

FWIW, the width of the current spindle appears to be ~109mm.

On the bike I took the new ringset off, the spindle is ~123mm (not including the threading protruding beyond the tapered spindle)

Does it matter if a spindle has protruding threads versus a tapped thread into the tapered shaft? (other than "one uses a nut, the other a bolt" to hold the cranks on...)

Thanks for the input!
ChrisBolt or nut type does not matter. Length is measured end of taper to end of taper. If the crank came off a 123 spindle,that's about what it needs to go back on within a narrow range.

Bolt or nut type does not matter. Length is measured end of taper to end of taper. If the crank came off a 123 spindle,that's about what it needs to go back on within a narrow range.


Excellent - that's all good to know. (I wasn't sure if the measure was end of taper to end of taper or otherwise)

BTW: is there any chance the chainstays would be too wide and interfere with the crank arms - even WITH the appropriate, 123mm spindle - or is that kind of spacing another standard?

Thanks again for the gold nuggets Sydney!

Chris

Excellent - that's all good to know. (I wasn't sure if the measure was end of taper to end of taper or otherwise)

BTW: is there any chance the chainstays would be too wide and interfere with the crank arms - even WITH the appropriate, 123mm spindle - or is that kind of spacing another standard?

Thanks again for the gold nuggets Sydney!

ChrisThere can be issues with big road rings and the wider mtb stays. Hard to know without sticking it together,unless you can eyeball how much additional clearance you would get with the longer spindle.