tech28

As you might remember my friend Alan Fraser and I traveled to Paradise
California to buy him a Triumph Trophy Trail just as winter set in. It
seems bad luck would not stop at the weather. Both Alan and I got colds
immediately on returning but we thought we got an OK bike in the deal.

I started looking the bike over to see what needed to be done to get
the reliability up to my standards, as Alan had asked me to do.
Initially between us we decided that it needed a Boyer Ignition with a
new dual spark plug lead coil, and a modern rectifier/regulator. Closer
visual inspection showed the need of a new rear sprocket, and new
cables (the installed ones end fittings did not fit the levers
correctly). And for reliability we decided to do away with the original
carb and replace it with a new correct Amal as old Amal’s slides tend
to stick at full throttle due to worn slides and distorted bodies (from
over tightening the hold down bolts).

So Alan went away and I started on it. I removed the rear wheel only to
find that the installed Yamaha wheel had metric bearings while the axle
was english sized, which made for a loose fit of about 0.050 inches. I
knocked out the bearings and the internal spacer. I then made a new
internal spacer with shoulders on each end onto which the bearings sat
and with a hole drilled to the english sized axle. Problem sloved! But
what wheel was this that was provided: a 1974 Yamaha, so said the
previous owner. But which model. After contacting Sprocket Specialist
with all the dimensions we got a sprocket for a 1974 MX250 that fit
perfectly. But the counter shaft sprocket was worn out too and that was
behind the clutch. So off came the primary cover. The previous owner
apparently didn’t see the need for a primary chain tensioner (or a
clamp to hold the alternator wiring out of the way of the primary
chain) so it was not in there. After removing the clutch and the
counter shaft sprocket door there was the sprocket. But wait, it looked
funny. The sprocket had hooked teeth and has been ground so as to be
able to run 520 chain instead of the stock 530 chain. You see the
Yamaha wheel’s sprocket is set up to run 520 chain. But why would a
person pay someone to grind down a worn out sprocket? In fact you can
run a mix of 520 and 530 sprockets using 530 chain without a problem.
We used to do it all the time years ago. So in went a new 20 tooth
sprocket (unground) to go with the 51 tooth rear. That will give the
bike about 96 MPH top speed which is a close match to my TR5T’s 99 MPH.
Through trial and error others have found that the gearing on my TR5T
is nearly ideal for dual sport riding. With the new sprocket and a new
530 chain the alignment between the front and rear sprocket was checked
(by eye) and found to be OK. Amazing, what with a Yamaha rear wheel and
a stock Triumph motor in a stock Triumph frame.

The front end was said to be off the same Yamaha (?) but when I
unloosened the front axle nut the fork leg spronged to a wider
dimension leg to leg. What? Apparently the front end is not a matched
set and the wheel is not centered when the brake backing plate is
seated against the fork leg. Further investigation showed that the
wheel and the extra set of legs provided with the bike by the previous
owner were a set. The wheel was never meant to be used with the
installed fork legs. In fact disassembly of the front end revealed 35mm
fork legs installed in 36mm holes in the triple clamps. The adaption
was done with crude sheet metal shims. Not good! So we decided to use
the correct 36mm legs supposedly from a Yamaha TT500. Once the correct
legs were installed the backing plate fit perfectly. The provided extra
axle [modified from some other bike(?)] fit fine after a short spacer
was installed on the other side of the wheel (other side from the brake
baking plate). It was necessary to push the fork legs well above the
top surface of the upper triple clamp to get the bike to ride low
enough. Fender clearance (between the top of the tire and the bottom of
the fender) was minimise. Of course, the oil was changed in the fork
legs before installation and was set six inches from the top of the
fork tube with the springs out and the tubes completely collapsed. With
the TT500 front end we ended up with 8 inches of fork travel.

Now to get ready for a new electrical system the components, the master
ON/OFF switch, the rectifier/regulator (Boyer Power Box), the dual
spark plug lead coil, and the Boyer Analog Electronic Ignition module,
were mounted on a triangular sheet metal plate and hung vertically from
the two bolts that in stock form were used to hang the battery box and
air cleaner box. That plate went on the right side of the main tube
while a much smaller plate, which had the 2.2 amp hour gel cell battery
tie wrapped to it, went on the other side. Neat! The lighting was
handled by a switch mounted on a sheet metal “dash panel” that used the
front two handle bar hold down bolts for support. That same dash panel
was used to mount a bicycle speedometer/odometer. A new old stock
accessory chrome head lamp (the original plastic one was held together
internally with duct tape) with high beam indicator was wired into the
lighting switch which had a center off, left for high beam and right
for low beam. That same switch also provided power to the rear tail
light but only when low or high beams (lights on) was selected. The
rest of the wiring was pretty straight forward with a hidden toggle
master ON/OFF switch on the electrical components plate. The Boyer
trigger wires were routed on the opposite side of the bike from the
rest of the wiring to reduce electromagnetic interferrence (EMI) that
might cause false ignition triggering. Each circuit carried its own
ground from a central ground stud on the electrical components plate
that had good conductivity to the frame itself. The latest Boyer
instructions revealed that a normal grounding kill button can be used
if the system is wired Negative ground (which it was) when that kill
button is connected to the Boyer module’s “coil” output. The battery
was fused and the brake light was wired so that, whenever the bike is
“ON”, the brake light circuit, which includes a switch connected to the
rear brake pedal, is operational.

Now for the carb. While the carb supplied was the correct 928,
disassembly revealed a 330 main jet with other components as per the
Triumph parts book. Since the correct main jet is a 180, I think the
bike was jetted a bit rich on the top. Funny it ran OK in the mid
range. Actually that is to be expected because the main doesn’t come
into play until the last 1/4 throttle. The new carb was installed
without a problem but being careful to not over tighten the hold down
nuts to avoid carb body distortion. The supplied K&N filter was deemed
too laborious to clean, requiring overnight to dry out after cleaning
and very special K&N filter oil. So a universal (ATV) foam style filter
was clamped directly to the carb mouth, which had been modified with a
screw on ring that gives a flat surface on to which to clamp.

While the installed exhaust system looked OK the oil could not be
changed without its’ removal. Not acceptable since the way to make a
Brit bike survive is to change the oil frequently. So it was decided to
have a new stainless system made up by our local Hesperia welder, Mark
McDade. The system was a two into one joining under the center of the
engine and exiting as a single larger diameter pipe under the swinging
arm, sweeping upward on the bikes right side. As always the fit and
finish were exactly as we requested and it looked great to boot with
it’s shorty muffler and SuperTrap end plate and baffles. The SuperTrap
components make it forest service spark arrestor legal, as it clearly
states on the end cap for all to see (including the forest ranger).
Through addition and deletion of baffle plates, the noise and power can
be tuned. Unfortunately, more noise equals more power and vice versa,
but at least you have options. Twelve baffles was selected as a
starting point.

At completion Alan took the bike for a little ride around his 10 acre
property and seemed very pleased. The bike looks good, seems to run
well, has no major oil leaks, everything seems to work as it is suppose
to work, and above all has that neat twin four stoke sound, not to loud
and not too muted.
What is to be learned from all of this? No matter how good the bike
looks the build quality is no better than the guy building it makes it.
My experience is that all these old Brit bikes have been worked on by
idiots. For me the only way to do it is to buy a complete, near basket
case and tear it down to the last nut and bolt. Paint everything real
nice and replace or fix every working bearing, seal, or worn/broken
item. Kind of like building it from the ground up. That is the way to
be totally confident of the end product’s durability and reliability.
Actually we got an OK bike, put about another $1000 into it (assuming
we don’t have to do the engine later), and ended up with a good
utilitarian bike-not like new but probably reliable and relatively
durable. Too bad that most of our time was spent fixing others poor
workmanship. It was still a bargain for Alan Fraser compared to my TR5T
(perhaps about half, but no engine work was done to Alan’s bike). I
would like to thank my good friend, Keith Moore at Moore’s Cycle Center
in Anaheim for providing the vast majority of the parts used here, in
an extremely timely manner and with his forever helping advice.