Quoted post said:Originally Posted by rwk123 [IMG]/img/forum/go_quote.gif[/IMG]
The worry wasn't actually that the new BB wouldn't simply fir the frame, but that the chain line would prevent me from being able to shift through all of the gears (I should probably have made that clear) - I went into my LBS the other day and I was regaled with a tale of just such a nightmare scenario happening.
While chainline is something to consider, it is NOT as important as it was 30+ years ago because of the evoluton of bicycle chain design ushered in (by my recollection) with the SEDIS NARROW chain which allows for more lateral flex AND which is a reason that a Triple can be used on a "Racing" bike which has relatively short chain stays when compared to the stays on a Touring bike ...
Chainline DOES remain important for Single Speed bike ...
FYI. About a dozen years ago, I put an old, square taper LX crankset mounted on a too-long 118mm spindled BB ... no problem.
More to the point, here is a more recent example where a Shimano XT crankset is mounted on a "normal" 113mm Octalink BB (the shortest available for Octalink V2 cranks):
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With the chainring mounted on the inner shoulder (i.e., where the middle ring would be located), the chainline is "off" line by 2-or-3 millimeters ... less than the width of the chain ... not perfect for a Single Speed, but close (or, close enough as far as 'I' am concerned) AND not so far off that there is any real friction.
- the frame's rear spacing is 120mm & the hub is a vintage Campagnolo Nuovo Record hub whose flanges are centered on the axle.
The point being that while the chainrings may be slightly more outboard with a MTB crankset, they will not be extraordinarily so ...
I do NOT know if a Hollowtech II MTB crankset's chainrings will be offset more the Octalink MTB crankset is offset ...
Of course, the over-rated Q-Factor will be much more outboard with a MTB crankset (~170mm) than with a Road crank (~150mm for a Double & ~160mm for a Triple).
Quoted post said:Originally Posted by rwk123 [IMG]/img/forum/go_quote.gif[/IMG]
I hadn't heard about the possible need to face the frame though, so thanks very much for the advice and I'll check it out - though I am a little lost in the instructions that you gave about the typing paper!?
So, if you were to take a paper towel core & randomly cut it in half, the odds are that the cut edge would not be perfectly square/perpendicular with the core's axis whereas the machine cut edge would-or-should be ...
- insert a rolled up piece of typing paper into the shortened cardboard core ...
- and then, unroll it
- and then, press one edge of the typing paper against the cut edge & square the OTHER edge
- you should be able to make the typing paper perfectly flush with the edge of the machine cut edge when the typing paper's OTHER edge is flush with itself ...
When you do the same thing to the other side of the cardboard core, you will see that the edge you cut will probaby not be square when you square the OTHER edge of the typing paper unless you did an extraodinary job cutting the core into two pieces.
You can do the same thing with most BB shells where the exception might be some lugged steel frames where the tubes where not carefully trimmed prior to being brazed OR if the bolt that holds the under-BB cable guide intrudes on the interior of the BB shell -- in the latter case, temporarily remove the bolt.
