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#Post#: 2766--------------------------------------------------
Swinging Arm issues
By: banquo Date: March 4, 2020, 11:46 am
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I noticed significant play in the swinging arm following the
Mighty Falcone's trip up the Stella Alpina, and although I'm
sure that the short but brutal trip wasn't the cause, the play
was bad enough that there was no point in putting off the
repair.
Having read of Mark's problems in removing the swinging arm
bolt, I was ready for a fight, but in fact the through bolt came
out easily, after removing the mudguard, rear wheel, sprocket
and chain, and the bolt was still shiny from its original
cadmium or zinc plating.
HTML https://i.ibb.co/vL9QJq8/arm.jpg
HTML https://ibb.co/VM6Qv98
Any optimism from this success was short lived though, once I
worked out how the pivot had been designed.
They say that the NF frame was designed by Tonti, and maybe it
was, but he must have either had an off day, or given the design
for the swinging arm pivot to his apprentice.
Unusually, the through bolt does not act as the axle; the axle
is a hollow thick-walled tube of about 26mm outside diameter x
about 18mm bore through which the through bolt is a sliding fit.
This steel axle pivots on a pair of STEEL bushes, which are
flanged, and the axle is slightly longer than the dimension
between the outer faces of the bush flanges, to give slight
end-float. The axle is compressed by two cup washers, that are
in turn compressed by the flanges on the frame, under tension
from the through bolt.
Cup Washers
HTML https://i.ibb.co/D15RmsW/cups.jpg
HTML https://imgbb.com/
Swinging arm bush flanges- note flanges of bushes are the same
diameter as pivot tube, making drifting out extremely difficult
HTML https://i.ibb.co/grNKT6z/flange.jpg
HTML https://ibb.co/b6T9B7z
Swinging arm bush drawing - note the diameter is wrong; it's
actually the outside diameter of the bush, not the internal
HTML https://i.ibb.co/SXLmFHq/bush-dimensions.jpg
HTML https://imgbb.com/
All of that is fine except for the following issues:
[list]
[li]There is no lubrication or sealing provided for the steel
axle or the steel bushes, so they both rust and wear[/li]
[li]As the bush flanges are the same diameter as the tube on the
swinging arm, it's not possible to drive them out easily,
because there's nothing to support the swinging arm on except
for the trailing arms[/li]
[li]As water and road salt make their way past the bushes, the
axle rusts between the bushes, and of course the rusted section
increases in diameter, so it's impossible to get the axle out
without applying brutal force[/li]
[/list]
I have never seen steel bushes in a swinging arm, but they could
have worked well, if the designer had decreased the diameter of
the axle between the bushes, to allow for rust, and also
provided a grease nipple, so that the axle and bushes could be
both protected and lubricated. If they had even greased
everything during assembly, that would have helped, but it's
clear they didn't..
Anyway, I had to get the axle out, so, after soaking everything
for two days in Plus-Gas releasing fluid, I supported the
swinging arm on top of a tube, and started to drift the axle
out. I tried a soft hammer and a soft drift, but neither had any
effect, so eventually I had to resort to a large club hammer and
a steel drift. Still the axle would not move, so I removed the
tube that was bearing on the flange of the bush, supported the
axle so it was resting on a trailing arm instead, and resumed
drifting, whereupon the axle came out, taking the lower bush
with it. I mananged to get the opposite bush out with a steel
drift, but I cannot overemphasise just how much brutal force was
required, despite all the prelubrication. The main problem was
the rust in the centre of the axle, but the steel bushes were an
interference fit in the swinging arm, and of course were
'welded' into place with rust.
Once removed, the wear on the bearing face of the axle is
obvious:
HTML https://i.ibb.co/0YNbPsB/journal.jpg
HTML https://ibb.co/BTDM8n4
This is after cleaning, so rust has been removed to expose the
serious pitting, and you can see the wear step between the
journal and the un-worn axle.
Here you can see the rust pitting of the centre of the axle,
between the bushes. Again, this is after cleaning all the rust
off with wet and dry paper, but I estimate that the axle had
increased in diameter by at least 1mm, and there was no way it
could be removed through the bushes
HTML https://i.ibb.co/ZxWMfLG/bush-axle.jpg
HTML https://ibb.co/gJzRrjm
My friend Tony had kindly offered to make some new bronze bushes
for the repair, but as the axle had been completely destroyed by
mushrooming the ends during drifting out, the problem was bigger
than that.
Initially, we had hoped he could turn a completely new axle, but
his lathe was not capable of boring the axle at 18mm for the
through bolt, and we could not find any hollow bar stock of the
correct internal diameter. On that basis, I resorted to asking
him to cut the bad ends off the axle, cut the remains in two,
and make a short section for the centre, to make up the
difference. At the same time, the central section was reduced in
diameter from 26mm to 25mm to give clearance for later
withdrawl. Normally a 3-piece axle would not be an option, but
as the only thing that stops it from turning is the clamping
force, and all 3 pieces will be centrally located on the through
bolt, I don't see a problem.
HTML https://i.ibb.co/48fJtrd/reduced-dia.jpg
HTML https://ibb.co/5r924HF
HTML https://i.ibb.co/ftrq4D3/new-axle.jpg
HTML https://ibb.co/sQsbyWT
The bronze bushes should be better than steel, and we have added
a grease nipple to the underside of the swinging arm tube, so
that everything will be protected and lubricated. The bronze
bushes are a sliding fit in the swinging arm tube, and will be
retained by Loctite 641.
The only worry we have is the end float, as I stupidly didn't
measure the axle length before drifting it out, and Tony has had
to guess how much longer to make the axle than the outer flanges
dimension to give some end float.
I'll find out if any adjustments are required when I put it back
together, and won't Loctite the bushes until I'm sure it all
fits, but that day will have to wait until I receive the powder
for powder coating it.
If only they had made it like this in the first place...
I'd strongly recommend that any owner adds a grease nipple. In
retrospect, I'd prefer risking getting some swarf in there, and
drill and tap it in situ (using grease to minimise the chance of
swarf entry), rather than do nothing, but if there's any chance
to dismantle it and fix it properly, I'd take that chance.
Mark's axle had seized into the bushes, and instead of the axle
swinging in the bushes, the through bolt was swinging in the
frame flanges, causing serious wear, and an even bigger
nightmare getting it dismantled.
You have been warned....
#Post#: 2767--------------------------------------------------
Re: Swinging Arm issues
By: monohorizontal Date: March 6, 2020, 3:16 pm
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salut c'est un des points faibles du falcone un graisseur serait
le bienvenu , moi je graisse bien et je règle le serrage de
l'axe du bras oscillant pour un jeux correcte et après mes
falcones ne roules jamais sous la pluie alors tout va bien
hi this is one of the weak points of the falcone a greaser would
be welcome, I grease well and I adjust the tightening of the
axis of the swinging arm for a correct game and after my
falcones never roll in the rain so everything is fine
#Post#: 2768--------------------------------------------------
Re: Swinging Arm issues
By: Vusette Date: March 11, 2020, 11:50 am
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Hello,
Interesting story!
Where will you drill the holes for the grease nipples?
As far as I can see, if you put them on the upper side of the
swingarm they will be difficult to reach with the grease gun.
On the underside, it's also difficult. And whats more, the
grease will have trouble to move around the shaft.
Philip
#Post#: 2769--------------------------------------------------
Re: Swinging Arm issues
By: banquo Date: March 11, 2020, 1:52 pm
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Nipple is on the underside facing slightly backwards. I have an
extended one in for now, but may change to an angled one once
I've checked the assembly.
Orientation isn't important, as you pump the whole cavity full,
until it squeezes out the ends; all surfaces should be pretty
much covered I think. I'll also grease the through bolt on
assembly.
#Post#: 2770--------------------------------------------------
Re: Swinging Arm issues
By: monohorizontal Date: March 11, 2020, 2:09 pm
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salut sur mon falcone rouge le bras oscillant était déjà percé
au dessus vers l'arrière et dans le milieu je n'ai jamais
installé de graisseur c'est la graisse qui bouche le trou mais
il serait bien avec un graisseur aussi
hi on my red falcone the swinging arm was already pierced above
backwards and in the middle I never installed greaser it's the
fat that clogs the hole but it would be nice with a greaser too
#Post#: 2771--------------------------------------------------
Re: Swinging Arm issues
By: banquo Date: March 11, 2020, 6:06 pm
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This is the finished arm after powder coating in RAL6014. The
powder was matt, but came out satin, which suits me, and matches
the rest of the bike pretty well.
HTML https://i.ibb.co/Gk70wcd/coated3.jpg
HTML https://i.ibb.co/pL03mdy/coated1.jpg
HTML https://i.ibb.co/8YXnH2F/coated2.jpg
#Post#: 2772--------------------------------------------------
Re: Swinging Arm issues
By: monohorizontal Date: March 12, 2020, 12:52 am
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très bien comme sur ma rouge avec le graisseur en plus c'est
parfait joli travail banquo
#Post#: 2965--------------------------------------------------
Re: Swinging Arm issues
By: smellybeard Date: May 29, 2024, 8:38 am
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So, four years later how is it working?
Would you change the way you did anything?
I ask as I'm about to undertake the same job.
#Post#: 2966--------------------------------------------------
Re: Swinging Arm issues
By: banquo Date: May 29, 2024, 10:28 am
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All fine so far, and I haven’t come up with anything better in
the ideas department. If doing another, and I do have another, I
might drill for the grease nipple first, and try to inject some
rust dissolving fluid into the annulus before attempting
disassembly. It was very, very brutal…
I’ll wish you good luck: hopefully you won’t need it!
#Post#: 2967--------------------------------------------------
Re: Swinging Arm issues
By: smellybeard Date: May 29, 2024, 12:07 pm
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[quote author=banquo link=topic=425.msg2966#msg2966
date=1716996485]
If doing another, and I do have another, I might drill for the
grease nipple first, and try to inject some rust dissolving
fluid into the annulus before attempting disassembly.
[/quote]
Excellent suggestion.
My (red) paint is in excellent condition, so I want to avoid as
much abuse as I can. Heat is out of bounds. I do have a 10 tonne
press and making up tools on the lathe to fit the job is also an
option.
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