Today's mechanical adventure
From
Frank Krygowski@21:1/5 to
All on Fri May 9 20:50:13 2025
On vacation, in a hotel room far from home. The Bike Friday came along
in its suitcase. Nothing athletic on tap; it's just for leisurely
exploring and local transportation.
The Friday does a "quick fold" in a minute or so, which is good enough
for throwing it in the back of a small car or taking it on a bus or
light rail. But fitting it into its suitcase for airline transportation
takes some disassembly. Front wheel comes off, drop handlebars are
removed from the tall gooseneck stem and split in half, that stem is
removed, as are pedals, etc. Packing it in the suitcase is tricky, a
sort of three dimensional Tetris game with oddly shaped pieces. The
packing takes me over half an hour, but unpacking and assembly is
usually much faster.
Not today.
As I was all done assembling (so I thought) I lifted the rear wheel and
pulled on the left shifter as I turned the cranks, to get the chain on
the chainrings. But instead of the usual result, there was a big SNAP, I
heard some little mechanical bit hit the wall, and there was a loud
grinding, ratcheting sound from the gear train.
That sound was from the bottom of the Shimano 9 speed front derailleur
cage dragging on the large chainring's teeth. The derailleur was in a
weird position, I couldn't shift it, and I was afraid of mangling it if
I turned the cranks.
The hotel is fitted with carpet specially designed to make tiny escaped mechanical parts* invisible. (*The technical name for such a part is a "pingfuckit.") I didn't know what I was looking for, but I spent at
least ten minutes searching. The only thing I eventually found was a
tiny flat washer, too small to fit a 5mm screw. I couldn't even be sure
that was mine. Who knows how many devices had exploded in this room?
Working with a clumsy folding bike multitool, I unclamped the derailleur
cable and took the derailleur off its braze-on mount. I could then see
that the short inner link of the parallelogram linkage had lost its
pivot, which seemed to have been a shoulder screw. More searching
yielded only frustration. How could such a screw have totally
disappeared? I tried substituting an ordinary metric screw, but it
really needed a thicker bearing surface for proper pivoting. If I were
home I'd have cobbled up some sort of sleeve for the screw, but here I
have only what I brought with me.
It then occurred to me that it may have come loose during the flight.
Digging around in the case, I eventually found the pivot screw. I was
able to reassemble the tiny bits, remount the derailleur and see it
shift all three chainrings.
AFAICT this failure had nothing at all to do with this being a folding
bike or traveling by air. The pivot screw just decided to abandon ship
at a weird time. I'm glad it happened at a place where I could
(eventually) recover it, and not somewhere on the road.
--
- Frank Krygowski
--- SoupGate-Win32 v1.05
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