My hollowtech bottom bracket is knackered and so I need to replace it.
My LBS did it last time but this time I’d like to do it myself partly because I’d like to have a got at doing the job but mainly because my LBS doesn’t have any workshop time this side of the Easter Weekend to do it for me.

My questions are…

Are there different sizes of Hollowtech BB?
If there are, how do I know what size I need?

Sheldon Brown is your friend –

Hollowtech II ® Two-Piece Cranksets: Shimano’s latest top-of-the line system is a two-piece crankset. One piece is the combined right crank and spindle, the other piece is the left crank. Hollowtech II uses separate bearing modules that screw onto the opposite sides of the frame. Since the spindle is part of the right crank, there’s no issue of compatibility. All Hollowtech II cranks work with all Hollowtech II bearing units.

Any crank that fits on one type of spindle will fit on all spindles of that type, but if the length is incorrect, the chainline/clearance will vary.

Shell width in millimeters:
68 for standard ISO/British
70 for Italian
73 for oversized ISO/British. This dimension has to do with what kind of frame the bottom bracket fits, and has nothing to do with the crank.
Length: overall spindle length in millimeters. This will determine the chainline and various clearance dimensions.

Shimano sometimes specs two different lengths for the same crankset. This usually relates to the diameter of the seat tube. The shorter dimension is normally preferred, but bikes with fat seat tubes may require the longer size to accommodate the swing of the front derailer.

Or are you talking about the original Hollowtech rather than the newer Hollowtech II ?

The info you need is almost certainly here somewhere –

http://sheldonbrown.com/bbsize.html

Thanks for your help

I’m almost certain it’s a Hollowtech II since the spindle is part of (or connected to) the right crank) I know this because I took it apart (and put it back together) when I replaced my chainrings.

I’ll check Sheldon Brown this evening when I have the bike and the internet in the same place

What frame is it?

What chainset do you have?

It’s 6/7 year old Boardman Pro and a Truvative chainset

Should be a SRAM gxp bottom bracket
Best thing is to fit a hope one with the gxp converter in the left hand cup

The bottom bracket leaflet will usually tell you how many spacers you need to use for a given bb-shell width.
Don’t forget you need the Hollowtech tool too. Can’t just bash it round with a flat headed screwdriver and a hammer…well, not really.