92 Rockhopper Comp BB

[Jamer]

Hi, hope the assembled collective on here can help me; I've recently changed the bottom bracket on my trusty Rockhopper. Alas, the old one has gone in the scrap bin at the Lbs and the new one is too wide,- the front mech will not now put the chain on the big ring.

Question is, - does anyone know what the original spec shimano bb was and whether a replacement is readily available?
TIA

Jamer

 

[Grumpy farmer]

Is the bike wearing it's original chain set? My 1991 rockhopper comp has a Deore LX chainset and is on a 122.5mm bottom bracket axle. I cannot remember if its a 68 or 73mm shell width though.

 

[Jamer]

It runs a Deore LX mech with FC M550 cranks and a triple SG chain set, - all original fit apart from chain rings. Having spoken to AN Other LBS today they suggested the fact that old Specialized run a 73mm width probably accounts for the wrong BB.

 

[Elysarian]

I assume you've tried adjusting the mech to account for the couple of mm difference?

 

[Grumpy farmer]

Yep it's a 73mm shell on mine. If they had put in a 68mm b/b then it's likely that your non drive side crank will be closer to the frame than it should be as well.

 

[Jamer]

I've tried unthreading the set screw limiter to the point that the mech is on the limit of it's travel. The chain will run in the guide but there is still not enough movement to hold the chain over enough to enable it to pick up the large chain ring, IYSWIM.
LBS guy I spoke to today is confident the original LBS will have no problem sorting the issue which has encouraged me. - I was in fear when I started this post that I had an old bike, with the wrong BB and the original which had all the numbers legible now consigned to the scrap bin!
Grumpy Farmer,- to answer your point; the BB appears to sit central in the bracket, the axle just appears too long. LBS guy today suggested that a 122mm was fitted when a 118 was more likely, - he suggested a BB UN55C would be right for a 73mm shell.