This is one of those lessons that was
born out of necessity. Hopefully someone else can profit by it. The
story has a happy ending, so you
can put the tissue box away now and just enjoy the ride.
A bit of history
before we go any further: Those folks that know me are well aware
of my severe case of gearheaditis. I never met a two wheeler I didn’t
like, and anything mechanical is worth exploring. I’ve got more
old bikes than my tolerant spouse cares for, while I continue to “stumble” upon
worthy causes and push the boundaries of her love. I invariably have
multiple projects going, all the while working as a mechanical engineer
for a thermal vision company and selling screw kits for VJM’s
in my “spare” time. Which brings me to my latest endeavor – one
1965 Honda CB450 K0 Black Bomber. Belinda, as she’s come to be
known, came to me as the result of an irresistible eBay auction. She
arrived a few weeks ago from California. She was running within the
hour from unloading at my house. Not running very well, mind you, but
she started and ran, nonetheless. This bike had sat in inside storage
since 1975 and though she wasn’t a perfect specimen, she wouldn’t
need a ground up resto job to be attractive once again. I did notice
that in the short time I had her running, there was no RPM reading
on the speedometer/ tachometer gauge. I never tried to run the bike
down the driveway so speedometer operation was never verified. A visual
inspection of the tachometer cable revealed an outside jacket that
screamed “broken cable” so I dismissed the problem for
that moment. In the weeks that have ensued, I’ve done a lot of
cleaning, polishing and refurbishing. The carburetor slides were stuck,
which explained the poor running, and sure enough, both the speedometer
and tachometer cables were broken at their input ends!
The
speedometer cable was one of the first replacement parts to arrive,
and I went
happily about installing it. As a matter of course, I always attach
the gauge end first with the cable retracted (when possible) a few
inches. After getting the nut tight I feed the inner cable back into
the gauge with a turning motion to engage the gauge drive properly.
It was a bit disturbing this time however, as the cable engaged and
refused to turn any further! Seems the gauge was frozen solid. A
quick investigation proved the same condition held true for the tachometer.
Oh yeah, More Work!
After removing the gauge from the headlight
bezel without any improvement the decision was there in front of me,
go
grovel
before the gods of eBay, wallet in hand, looking for a replacement,
or attempt something I had never done - the dissection of a perfectly
beautiful looking, but nonetheless dysfunctional piece of forty
year old Japanese (Fuji Electric) instrumentation. Well if I was going
to have to buy another one anyway, I might as well see the innards
of
this beast.
My assessment of the situation was that the grease or other lubricant
had hardened in the narrow clearance area between the outer threaded
nozzle that attaches the cable jacketing and the inner drive
mechanism that contains the square recess the inner cable engages.
If I could
perhaps engage the square drive with something stronger than
the inner cable I might break it free and be done with it. I
found
that one of
my smaller threading taps had the same square dimensions so I
double nut-ed it and stuck it in the drive. Try as I might, neither
gauge
would budge with the largest oomph value I was willing to apply
to the wrench. Engineers usually call this torque, but in this
instance oomph was what I was giving it. The meaning of this
early failure
was that I must take the unit apart to the point where I could
do
some
soaking and cleaning. Let the disassembly begin!
First thing was to split the beast open to get access to the
mechanical workings. This meant prying up the underside of the
chrome bezel
that surrounds the gauge.
This was done slowly and carefully
using an ordinary slot screwdriver. I went around the perimeter about
four times before I attempted to separate the halves. This is tedious,
but determines the condition of things when they go back together.
It took a bit more prying to separate the halves, but shortly they
yielded to my efforts. After things are apart you can use a pair
of pliers without any teeth and flatten and bend the metal just a
bit more to ease the reassembly process. Don’t make the side
completely vertical again as you’ll have trouble bending things
back over. With this step behind you, one can now remove the innards
from the housing. On the back side of the housing are eight small
screws. There are two pairs of four screws. One set of four can be
seen jutting through holes in the housing – leave these alone
for now. The set you want to remove are the other four (two for each
clock). The CB450 gauge had slotted screws while my CB77 unit had
Phillips heads. Remove these and set them aside. One of the screws
had an electrical lead attached to it. This is the case ground for
the lighting. Since the unit is rubber mounted this must be replaced
or the gauge lights will no longer work. The instruments can now
be extracted from the housing.
Observing the bases of the drives
revealed a lot of solid white grease, just as I had suspected. Gently
probing with dental picks I removed most of this, but the units were
still very frozen. I moved the needles and they were free and operated
easily. The drive on these gauges is quite simple. If you can envision
two short tubes one inside the other. The outer tube is connected
by an axial shaft that goes to the cable input. When the cable turns
this tube spins with it. The inner tube is also connected by an axial
shaft. This shaft has the indicator needle attached to it. There
is a very fine, calibrated, gap between these two tubes. When the
cable turns from input, be it tachometer or speedometer drive, the
outer tube spins with it directly.
The air in the gap between the two tubes causes a drag and begins
to pull the inner tube along with it. The faster the outer tube spins,
the more drag there is and the further around it’s rotation the
needle is pulled. That’s the end of today’s Physics lesson,
but you can understand that if it’s just the air molecules making
your gauge work, we’ve got a mighty precise little package here,
and it won’t take much ham fisted shenanigans to make toast of
the little bugger. My next step was to see if I could get the grease
between the lower drive parts loosened. I found an old aluminum can/cup
I had that fit things just right. I plunked the unit in and filled
it to just above the lower drive parts with lacquer thinner.
The solvent
could then work from the bottom up or the top down. I let the unit
sit this way over night. In the morning I was able to just barely
turn either drive by carefully grabbing the outer tube of each with
my fingers.
After an hour or so of turn and soak, turn and soak one pooped completely
free and turned with ease. The second came along shortly thereafter.
I was almost home. At the suggestion of one of the folks on our VJMC
mail list (thanks Damon), I then substituted some spray carburetor
cleaner for the lacquer thinner. While there was a bunch of crud
in the lacquer thinner, the carb cleaner was the coup de gras, and
the
crud flowed out like, well…… like crud!
While the soaking
steps were going on, I had fashioned a drive tool out of one of the
old cable inners. I just cut the square cable end off with about
an inch of the round cable attached. This I chucked into my variable
speed,
reversible drill. Most gauges turn clockwise, which means the input
on the backside must be counter clockwise, so unless you have some
odd gauges the reversible drill is a must. This tool can then be
used to work the gauge through its operating range. Ramp the speed
of the
drill up through the range. Don’t just jam it full on. This
will also give you an indication of the health of the rest of the
mechanism.
The needle should remain constant as you hold the drill at a particular
speed. If the needle tends to bounce wildly about any point, you
have additional problems with its function that will have to be addressed.
My last step before reassembling was to use my soak
container one last time. Instead of having a solvent fill, this time
I used
a light oil
(Marvel Mystery Oil) to make sure there was plenty of lubricant
where all had been washed away. I even elevated the temperature
of this “bath” with
a 50 watt reflector bulb shining on it, to help the process along.
After an hour of soaking, I removed the unit and wiped the excess
oil from the external surfaces. I was now ready to attempt putting
all
back together.
I cleaned all the pieces and polished the chrome ring. It is
especially convenient to do this while the unit is apart, you
can access areas
that are difficult when all the pieces are together. I also checked
all the light bulbs and replaced any that either weren’t operating
or even looked marginal.The caveat here is to keep a light hand!
You’ll
be squeezing and hammering on the unit, so remember you hold disaster
in your hand. I had a piece of plastic to use as a base, but a good
piece of wood will do the job too. I placed the assembled gauge,
face down, on this base and attached some clamps to hold
everything
in position. This would be a good job for an assistant’s
help, but can be done by one. At this point I was just trying
to get the
chrome ring back in position on the base. Even with opening the
ring more while it was removed, it did not drop into place. With
just
light clamping pressure applied a little more prying was necessary
to get
things together.
Once the housing flange has passed the edges of
the ring, you are now ready to fold the ring back over the flange,
thus
holding everything together again. I tightened my clamps until the
base was in its previous position inside the flange. I then used
a long drift punch and a 4 oz. Ball Peen hammer to gently fold the
ring
material back over the base flange. As with the process to remove
the flange, slow and easy is the watch word. I made at least three
trips
around the perimeter going just part way each time. Go easy and get
the feel for the effect of a particular force of hammer blow. It’s
much better to make five trips around than to shatter the glass cover
with a heavy blow.
I added one last step of dubious value, but I’m
anal retentive so assess the value of this step for yourself. I used
a small C-clamp and worked my way around the perimeter, one last
time. The effect of this was to add one last level of flatness to
the pryed
up ring, and to make sure the halves were clamped together as good
as can be.
OK. You’re done! Put the gauge back in your bike, connect the
electrics and cable and go off for a well deserved ride. Remember – watching
the road and traffic takes precedence over eyeballing the wonders
of your repaired gauges in action. As a follow-up I plan to get an
old
defunct gauge and tear it down those last few steps where all the
innards are laid bare. So keep on the look out for that article to
appear here,
at a date in the future.
