Lister wrote:
> I'm looking for an mtb crank to cut and re-drill for my 7 year olds
> bike. I found a Truvativ 5D. Anyone know if it's solid and otherwise
> suitable for this? Thanks.
I have done this modification to convert 185mm BMX cranks to 152mm
trials cranks. It's not as easy as it sounds.
You need a crank arm that is as thick through the arm (or more so) as
it is at the original pedal eye. It can't be much narrower across the
arm at the new pedal thread than it was at the old one. And you must
shorten the crank by enough length that the clear length on the far
side of the new pedal hole at least equals what was there originally.
That means at least 30mm change in length for most cranks.
You don't know what the particular material properties of your crank
are, so default to what the manufacturer did. The good news is that
your cranks will wind up stronger and much stiffer overall after you
shorten them.
My experience with Truvativ cranks is limited to the Stylo and the
Hussefelt. Either one of those would be suitable for retapping.
When I shortened a set of Primo Powerebites, I attached the arms one at
a time to the spindle, then mounted the spindle in a rotary table chuck
on a vertical mill. Then I was able to drill, tap, and spotface each
crank arm in one setup.
It would probably be possible to get decent results by using a drill
press and carefully setting up in a vise with v-blocks or the like. It
would not be a good idea to skip the spotfacing step.
Chalo Colina
