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Will a triple crank fit on this old BB ?(4 posts)

Will a triple crank fit on this old BB ?PeterRider
Aug 8, 2002 6:55 PM
I am trying to repair an old schwinn road bike that i found in the bike room at school, just for fun. There is a shimano rear derailleur RD-TY20, so I guess it is a 93 or 94 bike.

There was no crankset on the bike, and since the only cranks available in the room are triples from mtbikes (I don't want to invest any money in this operation), I guess I'll go triple. The front derailleur on the schwinn is a suntour with long cage, so it was a double setup. I took the bottom bracket out, the only inscriptions I see are MTBS504 and C.M.3S. It has a square end with a threaded part at the end, and bearings that come apart. I don't know how BB are measured usually, I measure approx. 146mm from end to end, and 126mm from end to end of the square part. To me, MTBS looks like it could be "mountain bike"...

How can I find out the make ? and also, would a triple crank fit on it ? well, sure, some will say "just try", but i need to get a crankpuller to remove the cranks from another frame, so I can't try just now. Was just wondering if somebody had any idea. Should I provide other information ?


re: Will a triple crank fit on this old BB ?Rusty Coggs
Aug 9, 2002 4:35 AM
Square taper spindles are measured end of taper to end of taper.Double cranks typically use a shorter spindle than triples,but many old doubles used long spindles and newer mtb triples use somewhat shorter spidnles.....Bottom line, no way to know for sure, but that 126 mm meaasurement would be tto long for most triples...the cspindle length has to match the crank or the derailer will not have enough travel to reaach the big ring if too long or will not shift to the small reing if too short.....Bottom line,If you do not know the spindle length the crank takes,you have to try it.Bsst bet,maybe is to use crank AND bb from one of the mtbs.
If you don't want to spend money, you'll have to spend time.Spoke Wrench
Aug 9, 2002 5:36 AM
Sooner or later, you're going to have to get a crank puller or you won't be able to complete the job anyway. Just get one and do the trial fit thing. Nobody is going to be able to tell you for sure what bottom bracket you need.

The trick on a project like this is not to spend any money AT ALL for parts. Once you spend the first dollar, there is a tendency to keep spending more money so that your investment up to that point won't be wasted.

I'd do whatever I had to to keep the same front derailleur. If you're not too picky, with friction shifting, almost anything will do the job anyway. If you change it you are almost surely going to have to buy a new derailleur cable.
damn... was planning on buying new cables !!!PeterRider
Aug 9, 2002 8:39 AM
The crank puller will be paid by the bike club. But I was planning on buying new cables, all the cables I find in the bike room are somewhat rusty.

I want also to remove the front derailleur which is quite rusty, and put instead a triple from a mtb...