Dear all,
I've had problems with the bottom bracket of my 2001-vintage touring
bike for the last couple of years. I'm already considering acquiring a
new bike, but I wonder whether the old one is absolutely beyond repair.
Here are some pictures:
http://radio-bip.qc.ca/Palier/photos.html
The original Shimano cartridge-type bearing assembly began to wobble
about two years ago (pictures 13 and 14). This initial trouble was
caused by the ball bearing itself.
I thought it would be a simple matter to replace the faulty part, but I
was wrong.
I purchased a replacement cartridge (not cheap, if I remember well), and
the corresponding crank extractor (pictures 2 and 3), and attempted to
remove the crank.
After screwing the tool into the crank (pictures 4-6), I carefully
started rotating the wrench in order to pull the crank, but to my horror
I realized that I was actually very carefully stripping out the thread.
(I think it was more a design flaw than an error of mine).
I tried in vain to extract the crank using other means, so ended up
bringing the bike to the shop. The part was replaced, but the mechanic
told me he cussed a bit during that job.
The old bearing showed signs of aluminium [a.k.a. aluminum] corrosion
[pictures 8-13], see the pitting on the ring, in addition to the rust
desposits from the frame on the threads, or what seem to be left of
them. I remembered at that point my engineering school lectures and the
stern warning putting dissimilar metals into contact. But, hey, if there
are millions of bikes like that out there, why should I worry?
I had no complaints about the replacement bearing until it conked out
around Christmas 2007. The threaded fastening cup on the replacement
Shimano part [which played the same role as the one on picture 9] was
made of plastic, and now that I thought of it, the mechanic hadn't
screwed it in entirely, probably because the rust prevented him. Now the
bearing assembly was resting on only one side, and there was a huge
amount of play.
This time I was decide to do it myself. I tried to remove the crank, but
the thread was still gone from the time before, and no amount of
cajoling or violence could get the crank unstuck (pictures 15-16). I
tried heat and WD-40, too.
I bought a replacement Shimano crank assembly of a different design for
about 55 EUR, including which seemed of a better design (see pixes
17-25), and included cranks and sprockets.
Here's an exploded view:
http://radio-bip.qc.ca/Palier/EP1342656.pdf
Since I had a replacement for everything, I felt I could let loose my
butcher instincts, and hack away at all that junk which had made a
pedestrian of me for some weeks (pictures 29-38).
With the old bearing assembly out of the way, I was finally able to
inspect the damage (pixes 39-41). I had never before disassembled a
bottom bracket, so I wasn't sure whether this amount of rust was normal.
Ah yes, the pictures also explained why the lighting system shorted out
a few weeks before the trouble with the bearing reoccurred. I had
attached a new wire on the frame's surface with tie-wraps a few weeks
earlier.
After cleaning the socket with a wire brush (#47) and applying some
rust-remover, I was able to see that many threads were entirely gone
(pixes 50-51), and the ones which remained were not in very good shape.
I installed the new assembly (discovering that there was a prescribed
torque for the screws and cup). The cup on the drive side had very
little thread to catch, so I put two of the three O-rings on the left
side. The third one was not necessary for the socket width.
The result can be seen on pictures 52-54.
Alas, the repair held only a few weeks. The right cup fell out of its
thread, but is still held in by the crank, so the bike can be ridden
[pictures 62-63]. So I'm back to wobbly cranks and front sprockets
perpetually stuck at the middle setting.
So what can I do now? Is the thing ruined forever? Is the bike
dangerous? I can ride around the neighbourhood on that thing, but not
much more. It's a shame, as I think I maintained this bike generally
correctly. (Some tell me my problem stemmed from a manufacturing error,
as the socket should have been drowned in grease. Others tell me I
should have regularly greased the saddle tube to prevent water from
seeping in, an idea which I found rather curious in earlier days).
Another mechanic suggested I drown the thing in two-component epoxy glue
formulated for metals - that would last me for the remainder of the
bike's useful life. I found a product in the Uhu catalog, but no
retailer seems to carry it. I found a putty of the brand "Pattex", but
the load would quite probably exceed its specified limit, and there is
the problem of properly filling the gap between the cup and the socket
with something of the consistency of, well, putty.
Any ideas? Is there a way to save this bike. BTW, I'm a big, heavy, and
strong guy.
Thanks,
Alexandre
ps: sorry for the saga-like explanation, I could have started with the
current situation, but I thought that the full story would better convey
my current, frustrated, state of mind.