dvt <
[email protected]> wrote in message news:<
[email protected]>...
[snip]
Dear Dave and others,
I finally found some so-so picture of a 1970's trials motorcycle's trailing-arm chain-tensioner.
http://home.connection.com/~dank/montesa.htm
It's the short trailing arm hanging down from the swing-arm, pointing backward. Unfortunately, the
arm is the same silver color as the rear wheel rim behind it.
You can actually see the chain-tensioner arm better in picture right-3, looking through the wheel's
spokes from the other side.
A powerful wound spring forces the trailing end of the arm (and the chain slithering over the pad)
up toward the swing arm.
Such arms survive in deep mud, heavy brush, vicious rocks, and all sorts of other abuse, far worse
than pavement-oriented fixed-gear bikes ever face.
Again, whether such arms would be of any practical use is quite another question. I'm just puzzled
to hear that such an arm would be torn off by a fixed-gear bicycle---no forces that I can see will
trouble it in the slightest.
The chain rubs against the block, sometimes faster, sometimes harder. This rubbing wears away the
block pad or spins a sprocket, but the chain always moves in the same direction.
The chain also tightens and slackens, according to acceleration and deceleration, but any increase
in tension merely pushes the spring-loaded arm down a bit in an utterly harmless fashion, which is
what it's designed for.
So much for chain tensioners--maybe someone will be explaining something that I've failed to see.
Now for skid plates and nostalgia.
Visible in several pictures is the truncated back end of the skid plate that exposed the clutch-arm
underneath the transmission. The badly dangling clutch-cable can be seen in picture right 1 and
needs to be tucked onto the downtube, but the arm is not really visible, although I kinda-sort think
that I glimpse its very end.
The odd little silver disk on the black right-hand swing-arm near the pivot is a metal cap.
(Pictures right 1, left 2, and left 3.) You were supposed to unscrew it, fill the hollow arm with
chain-oil, and adjust a drip-feed in front of the rear sprocket to dribble oil down a piece of
flexible tubing and onto the lower chain run. The spigot is visible if you know where to look, but
the plastic tube has been removed. (Yes, this whole idea was idiotic.)
The round shiny silver can held tools. Why Montesa put it on the kick-stand side is unclear--the
tool pouch fell out when you opened the tool can, leaving you no place to put the tools that weren't
in use. It was hard to get at anyway with the bike tilted over like that.
Note the shiny metal fenders that rarely survived much riding. (The mudflap is missing from the
front fender.)
The black accordion fork gaiters are either an add-on or else indicative of a slightly later model.
Spanish fork springs were notorious for sagging.
The amusing speedometer is tucked behind the right front fork leg and provided legality. Bultaco's
machines had a rear wheel drive speedometer tucked up under the right front engine case, next to the
down-tube. Neither speedometer was much more than ornamental. (More legality could be provided by a
lighting circuit.)
The short-lever forward-mounted kickstart and lack of primary kick-start gearing meant that you
ended up stuck on a precarious climb, trying to coax the dead beast into neutral and then trying to
kick it back into life from well below the lever, all while trying not fall back down the hill. With
primary kick-start gearing, you can just leave it in third gear, whip in the clutch, and kick the
starter. (Yes, serious hills were usually climbed in third gear.)
The Amal carburetor had a tickler button instead of a proper choke. Pressing the tickler opened a
tiny valve that let gasoline rise and spill into everything, which you then hoped would catch fire
internally. The gas dribbled out onto the transmission case. If the engine started, you ran it until
it warmed up--there was no choke-lever to adjust. Sensible people replaced Amals with Mikunis, which
had far more choices in needles and jets (important in Colorado, where events were held between
5,000 and 13,000 feet) and a true adjustable choke-style device instead of a tickler.
This Cota is newer than the first model, which had a huge, touchy front brake inherited from a road
machine, but it's old enough that it has straight engine cooling fins. Later fins were curiously
wavy, theory suggesting that the slightly increased surface area dissipated more heat at low trials
speeds with little airflow. (Nowadays, water-cooling rules.)
A second spark-plug hole allowed fitting a compression release worked by a little lever next to the
clutch, not installed on this machine. The compression release made a huge noise, eased kick
starting, and could be used quite effectively for rear braking on downhill stretches.
Unfortunately, a compression release also covered the engine with black two-stroke exhaust filth. In
real life, this dreadful black mung would be oozing from the engine/exhaust joint, due to bad
design. No sealant ever worked. Only a re-design stopped Montesas from drooling. (Bultacos ran dry.)
Despite all these quirks, I'm glad that the owner discreetly omitted the price for what looks like a
machine in excellent condition. I'm hoping that gazing with senile pleasure at the pictures will be
enough. A low price might tempt me to folly.
Carl Fogel
