Bottom bracket size/type for Alpinestars Cro-Mega?

[richierich66]

Can anyone help me please? I have a Cro-Mega LX (not the elevated chainstay one) and I cant find what size BB I need....Sorry, should have said, I have a Shimano BB-UN50 that I took off my MongooseIBOC Comp of similar year (early nineties) but I read somewhere that Mongoose used different thread sizes to other manuf? Also the BB-UN50 doesnt seem to be available to buy new now. Will a BB-UN53 or 54 fit the Alpinestars?
Thanks in advance...Rich

 

[drystonepaul]

Hello Rich
The Bottom Bracket shell on your Cro Mega LX should have a standard BC1.37x24 thread and as such means that you'll be able to use pretty much any of the standard Shimano cartridge BBs.
These include the UN53 and UN54 that you've mentioned as well as the cheaper UN26 and the more expensive UN73 if you can still find them. These all have square tapered spindles and work with practically all square tapered cranks.

The main points to consider when buying a replacement are:
1: Shell width - either 68mm or 73mm
2: Spindle length - this will vary according to what crank you use.

Typically older non low-profile and non compact drive Shimano cranks from around the same period as your Alpinestars ie pre 1993, will use a 122.5mm spindle. eg 1991 DX cranks.
Later low-profile cranks tended to use shorter spindles eg. 113mm for 1994 LX cranks.

Hope this helps

 

[richierich66]

Paul
Thanks very much, that's very helpful. Just measured up both frames and the mongoose had a 68mm shell whereas the as has a 73mm shell so I guess I would have had to buy a new one anyway...