tech19

In the past few years I keep hearing and seeing on the Internet the
same questions. People want to know so here are the questions with
some answers.

Why two ignition coils; two sets of points?

ANS: Lucas was trying to eliminate the distributor used on earlier
bikes. In fact, one set of points can be used with a double ended
“Harley” style coil, which will fire both plugs at once: one at the
correct time and the other during the exhaust cycle, doing nothing
good or bad. Using two coils on one set of points works but will burn
the points sooner reducing their life.

Why four condensers on late dual points Brit bikes?

ANS: The condenser does two tasks; reduces points arcing and acts as
part of an oscillator circuit with the coil. If the condenser is close
to the points it nips the ElectroMagnetic Interference (created by the
arcing) locally, not letting it circulate in the system wiring, which
could make the wiring act like an antenna, broadcasting the EMI. The
same is probably the reason for putting another set of condensers
close to the coils. The sharp rising voltage in the coils at firing
time also creates EMI which could use the wiring as an antenna. The
system only “needs” one set of condensers and cares little whether
thay are under the tank or inside the points cover.

Why strobe time a Boyer and why does my Boyer equipped bike no longer
run as well as when the Boyer was first installed and why did my Boyer
equipped bike seize?

ANS: The ignition timing is critical. Lining up the white paint dots
at Boyer installation time is not accurate enough. The timing must be
checked and set using a stroboscopic timing light. The problem I have
seen on more than half the Boyer installations that have been through
my garage is that the taper on the magnetic trigger assembly is not
machined very well and the assembly can slip and change the timing, so
much that the bike will stop or seize. Make sure the hold down allen
bolt is not bottoming, use a spring lock washer under its’ head, and
use locktite on its’ threads AFTER strobe timing adjustments.

Why are there intermittent electrical problems on my 30+ year old Brit
bike?

ANS: It has seen 30+ years of moisture, vibration, and tinkering. I
always rewire my personal bikes, not using an after market harness. I
do a point to point wiring scheme, well planned out on paper first,
bundled using shrink tubing and corrugated split tubing, correctly
crimped on end fittings (soldered if possible), with shrink tubing
added at critical points, and using a single point grounding scheme.
The single point ground scheme includes a return wire (ground) for
every electrical device, carried back to a single frame point, if at
all possible. This eliminates the number one intermittent problem:
loose mounting hardware destroying the device return (ground ) path.

Why are Energy Transfer (ET) ignitions perceived as unreliable?

ANS: Because they basically are unreliable. The earlier ones used non
encapsulated stators and coils that short and open under the high
vibration of the off road Brit bikes they appeared on. Both set of
points must be perfect in order for the bike to run at all (in twins
only). The ET system voltage is 6 volts AC and is easily lost to bad
connections, compared to a 12 volt system. Some versions of the ET
stator require that the brake light be connected to the low voltage
circuit of the ignition. Any short in the brake light circuit and the
ignition goes away. Touching the rear brake while coasting to a stop
can kill the motor. The rotor on the end of the crankshaft must be
timed to the firing point of the spark plug or the spark will be less
than optimum intensity. When wired up for lights the results are very
dim, pulsating head and tail lights.

Why do I need a battery on my Brit bike?

ANS: You don’t. The large Lucas capacitor (spring mounted) can be used
instead of the battery. If you select the right after market solid
state rectifier/regulator then the battery and the large Lucas
capacitor can be dispensed with. The name brand units that allow this
are Boyer Power Box and the MittyMax. The Tympanium and Podtronics
require the battery or the large Lucas capacitor.

Why does my BSA A65 have low oil pressure?

ANS: Several reasons can cause this. The most prevalent one is a worn
timing side crankshaft main bearing bushing. The crankshaft end play
shims are so thin they can tear and fall out, accelerating the timing
bush wear and allowing oil to bypass going into the crankshaft and
going right into the sump. With such a free path the pressure doesn’t
build and the rod bearings get starved of oil. The earlier BSA rotary
oil pumps become distorted from over tightening or perhaps old age and
fail to deliver the correct quantity of oil with each revolution.
Later cast iron pumps are a better choice than the original brass
ones. But this problem, perhaps well hidden since few BSA A65 have a
means to measure the oil pressure, has no clear cut source or answer
as I continually see this question on the Internet without any found
solution.

Why doesn’t my Brit bike stop good?

ANS: In some testing we have done on our vintage MX race bikes and on
my vintage street and dual sport bikes we have found that the brake
shoes are not arced to the drum. That is, the shoes don’t contact the
drums on 100% of their surface. What we found effective is to glue,
using contact cement, some 100 or so grit sand paper, cut to the exact
width and circumference, to the inside of the drum, sand toward the
brake shoes. Install the backing plate with shoes in place and then
the axle. The brake is applied firmly while rotating the backing plate
in reference to the drum. What happens is you are sanding the high
spots off the shoes. Pull it apart, removing the brake dust and
replacing the sand paper as required until you see that the shoes have
100% contact. This can be detected by a freshly sanded surface on the
entire shoe braking surface. The contact cement allows easy removal of
the sand paper. Brake improvement can be phenomenal. On double leading
edge brakes be sure to adjust the lever to lever linkage so that both
shoes touch the drum at the same time. Turnbuckles allow such
adjustment.

Why does my fiberglass gas tank leak?

ANS: Recently added lead substitutes (MTBE and alcohol) apparently
dissolves polyester resin that is and has been used for decades in
fiberglass gas tanks. In a recent fiberglass fabrication text I have
read, it was stated that vinylester resin was developed to coat piping
used to handle caustic and hazardous chemical. If a person were to
coat the inside of a leaking fiberglass gas tank with vinylester resin
maybe the tank could be saved. My personal experience with fiberglass
gas tank leaks led me to replace the fiberglass unit with one made of
aluminum.

Why does my steel or aluminum gas tank leak?

ANS: Brit bikes vibrate. And if the gas tank is allowed to touch any
metal part of the frame or engine, the thin sheet metal will be
machined through by that juncture. Rubber mounting that is decades old
can and does fail allowing the tank to settle on the frame or the
engine. Engine head studs do wonders to the bottom of an aluminum
tank: instant leak. There are commercial coatings for the inside of
gas tanks (don’t use the ones for metal on fiberglass) but first fix
the leaks by welding and use the coating to keep any rust from
spreading inside the tank.

Why is my motorcycle seat so hard?

ANS: Factory foam softness is controlled by casting in blanked off
holes going from the bottom up to the overall top foam. After time the
walls between the holes rot or tear and many holes becomes fewer big
holes. The result is you rear end sinks through the torn foam to the
seat base. Use an upholstery shop that specialize in motorcycle seats
to get a replacement that is either not too hard or too soft. Avoid a
layered and glued together foam carpet pad as it is more glue than
foam. A cast foam real motorcycle foam is the best choice.

Why all the problems with old Amal Carbs?

ANS: Amals were and are (currently still available as new) made of
“pot metal”, both the body and the slide. Two similar metals when run
against each other will gaul, which is the effect of one surface
transferring to the other. This makes the slides stick and wear
excessively fast, leading to loose slides that can cock in their bore
and stick (usually at full throttle). A common fix is to rebore the
slide hole in the carb body and press in a stainless steel or other
material sleeve. Sleeving a carb is no permanent fix as there is
another problem with Amals: body distortion caused by over tightening
the mounting flange nuts. Such over tightening may make the slides
also stick. Once the flanges are true and the slide bore and slide are
good, the correct tightening approach is to: 1) use the special O-ring
between the carb and the intake manifold; 2) use self locking nuts
(special low profile ones are available through your vintage dealer;
3) tighten the nuts only tight enough so that the carb body can still
be moved on the manifold with one hand; 4) seal the carb to manifold
junction, if you wish, with black vinyl electrical tape. Rather than
re-bore the original worn out old carb I always choose to replace the
carb with a brand new Amal, being careful to not over tighten the
flange mounting nuts. Sure, the slide and body of the new unit will
eventually wear out, but probably not in my lifetime.

Why are some Brit bikes positive ground and others negative ground?

ANS: Vehicle manufactures, ever aware of costs, use the frame of the
vehicle, which is normally a electrically conductive metal, as one of
the two paths required in any electrical system. The choice of
positive or negative ground is arbitrary and the Brits at first chose
positive ground while us Americans chose negative ground. Either
works, but some components on a Brit bike rely on the choice of
positive for ground: the selenium rectifier and the zener diode. If an
after market rectifier/regulator is chosen to replace the Lucas stuff
the whole bike can be converted to negative ground at that time,
assuming you plan a total rewire, too.