FITTING MID BOTTOM BRACKETS ??

[HARORIDER]

What is the correct way ? does the spacer+both bearings when "offered up" together have to be exactly the same width as the mid bb shell ? tried one today and felt tight so put another spacer in and still the crank felt quite stiff  if i put another spacer in then the bearings would not be flush with the outside of the mid bb shell 

[Munnyella]

Should be a step in the BB shell, the bearings sit against that, it (the step) should be the same width as the spacer.

MM

[TwoBobRob]

^^^^^^^^

...is the right answer.

Cast your mind back to the old days of US BB fitment and they always said make sure one bearing sits ever so slightly proud of the cup. The idea being that all loading from the crank arm bolts is transmitted through the bearing inner race and tube spacer without loading the bearing and outer race at all - which would be bad for the bearing and is what gives you a tight crunchy BB.

Mid schoolers may very well tell you summat different though; pretty much all of us did away with the spacer altogether so we could run the cranks deliberately tight so they didn't move on no footers.

[HARORIDER]

The total width of the bearings, tube spacer and ring spacers should be about 0.5mm wider than the BB shell.