tech47

What should we do to our vintage project bike to assure the ultimate in
reliability, or nearly so? I would break the effort down to areas of
the bike: the engine mechanicals, the electrical system and
carburetion, and the chassis.

Part One-The Engine Mechanicals:
Old engines need work on the valves, the pistons and associated bores,
the crankshaft and rods, the transmission, and the primary components
including the primary chain and the clutch assembly.

For the valves disassemble the head keeping all the parts separated and
identified as to where they came from. I take the head to my dealer
where he uses go/no-go gages he made up to measure the valve guides for
looseness. He measures the valve stems and the free length of the valve
springs. Anything that is out of spec should be changed. New valve
guides means that the valve seats in the head must be re-cut. The same
is true if new valves are installed. The valves may only need to be
re-ground. It is not normal to have to replace the valve seats in the
head but it is possible and is a big job. It is almost better to hunt
down a good head to replace one that needs seats. I measure all the
rocker pivot holes and the pivot shafts, and replace either if they are
too loose and out of spec. If any of the push rods are bent they get
replaced. Any looseness in the cam followers in the base of the
cylinder may mean new tappet blocks and/or followers. That is
especially true if there is excessive wear on the cam follower surface
that runs against the cam. The followers should be replaced if the cam
is replaced as the two wear into each other and old followers can wear
out a new cam. With the barrel removed it is usually easy to see the
wear on the camshaft working surfaces. If worn, the cam will have to be
replaced (and the followers).

For the pistons and bore, the piston should be removed from the rods,
the rings carefully removed, and the pistons and bore measured to
determine if all is within spec. A feeler gage pushed between the
piston and the bore wall when the bare piston is inserted upside down
is not a bad way to grossly determine the wear. But the measurement
must be done in six spots: top, bottom, and middle, inline with the rod
motion and 90 degrees to it. The piston must be measured on the thrust
face about 1/2 inch up from the bottom of the piston. Record all the
measurements and determine if the clearances vary more than 0.001
inches top to middle to bottom. Also the allowable piston to bore wear
clearance spec should not be exceeded. Installing loose pistons can
lead to broken piston skirts and major engine damage. At a minimum the
bore should be honed and new rings gapped (use the piston to centralize
the rings in the bore and feeler gages to measure the ring gaps). File
the ring ends to get the right clearance but if too loose install the
next oversize ring gapped to the correct spec (this is a stop gap
measure and nothing is better than a fresh bore job, new pistons, and
correctly gapped new rings). Most Brit bikes want a piston to bore
clearance of about 0.004 inches but follow the instruction that come
with the pistons, as they are the determining factor. Piston pins
should be a tight sliding fit in the piston and a smooth sliding fit to
the rods. If new piston pins are loose in the rod the bush in the small
end of the rod can be replaced and reamed to size but if there is no
bush the rod will have to be replaced or a bush fitted, if possible.
New pistons demand new piston pins and keepers. Reused pistons need al
least new piston pin keepers.

The cases should be split and the crankshaft removed. The rods should
be removed and the crank rod bearing surfaces inspected for excessive
wear. A micrometer can be used to measure the crankshaft journals but
do not scratch the journal while measuring it. During the removal of
the rods keep each rod’s parts together and identified as to where they
go and how the caps are fitted to the rods and the direction the rods
are fitted to the crankshaft. New inserts and rod bolts are a minimum
and the crank may have to be re-ground. The crank should have its
sludge trap removed and the crank and the trap thoroughly cleaned. The
retaining plug may be difficult to remove but drill out the punch marks
and if all else fails use a pipe thread easy-out on the plug and then
replace the plug with a new one. Use blue LockTite on the threads and
then re-punch the crank to retain the plug. When reassembling the crank
and rods use a torque wrench as per the manual. Some manufactures like
you to measure the rod bolt stretch to determine if the rods bolts are
at the right torque. On ball and roller motors the right thing to do is
to replace all engine case bearings but I have found that if they run
free and smooth and there is no visible damage to the races or rolling
elements, they are probably good to go. With plain bushing motors the
crankshaft bush should be replaced, and line reamed to size (special
reamer with a pilot that extends to the good bearing on the opposite
side of the assembled cases). A good dealer will know whom to send you
to for this kind of machine work. The transmission bearings should all
be checked for smooth running and race or rolling elements damage.
These bearing are relatively cheap so changing them out will not break
the bank. If the crankshaft bearings are replaced be sure to fit the
correct ones (like Superblends on Nortons). Inspect all gears for chips
and engagement dogs for excessive rounding. There will be some rounding
but your dealer should know what is excessive. The shift plate that
moves the shifting forks should be checked for worn areas along the
tracks for the shifting arms. A new shifting plate could do wonders for
the shifting of the bike if that has been a problem area. The shifting
forks should be measured and inspected for wear and bending. The groves
on the gears in which the forks ride should also be checked for wear.
The transmissions on the Brit bikes are usually pretty stout but the
weak point is definitely the shift plate. The detent spring for the
shift plate should be replaced with a new one to get positive shifting.
It is possible for the lay shaft and/or the main shaft of the
transmission to be bent so do check for that if there is other damage
in the transmission, The kick starter mechanism should be inspected and
parts replaced as necessary. The return spring gets terrible abuse by
the mechanism so replacing the return spring is probably a good thing
to do.

For the primary the chain should be inspected for excessive wear
(stretch). The clutch should be disassembled and the plates inspected
for wear and flatness. On models with rubber bumpers in the center of
the clutch hub it is a good idea to replace those as they break-up with
time. The clutch basket should be checked for excessive pounding marks
where the clutch plates tabs insert. A file and a little effort can
remove the worst of the damage but all such baskets show some of that
pounding. The tabs on the clutch plates will show the effect of the
pounding and a file can save an otherwise good set of friction plates.
Don’t overdo it as there is a spec on the width of the slots and tabs.
Failure to fix this can lead to a grabby clutch action as the tabs on
the friction plates catch on the grooves in the clutch basket as the
clutch is pulled in and released. Renewing the pressure spring(s) is
also a good idea as they do eventually take a set and the clutch will
start slipping. For a bike that has a slipping problem going to
heavy-duty springs is sometimes an option. Disregard the wear of the
chain tensioner if so equipped unless it has worn down through the
rubber surfacing. The design is that the tensioner wears until the
rollers of the chain rub on the tensioner facing and the wear stops, as
the chain rollers now will roll over the surface with minimal wear.

Vintage Brit Motorcycle Restoration,
Part Two- The Electrical System and Carburetion

The key to a good starting and running Brit bike is a good ignition and
good clean carbs.

The Electrical System:
Most of the Brit bikes use an alternator, a rectifier, a regulator
(Zener diode), and a battery to develop a solid source of 12 volts DC.
To gain the maximum of reliability I believe the rectifier stack and
the Zener diode should be replaced with a modern rectifier/regulator
module like the Podronics, the Mity Max, the Tympanium, or the Boyer
Power Box. I have had direct experience with the latter two and both
work satisfactorily. The Mity Max and the Boyer Power Box offer
batteryless operation but for street bikes that is not a good choice
legally. All connections in the system should be clean and corrosion
free and all grounds should be verified to have good connection to the
ground terminal of the system battery. All wiring harnesses should be
check for shorts or opens or the bike completely rewired with 16 or 18
gage wires (perhaps 12 gage for the battery circuits). The engine
should also have good continuity to the battery ground terminal as the
spark plugs need to use the engine as a return path electrically. All
switches must be in good condition electrically. And the battery should
be fresh and fully charged before ever being installed in the bike.
Once installed the electrical system should be tested for correct
operation: battery terminal voltage at 13.5 to 14.5 volts DC from 3000
RPM to max RPM. The ignition should be replaced with a Boyer Electronic
Analog Ignition system. It replaces the points, the mechanical advance
mechanism, and the condensers. On twins or triples you should also
replace the coils with the correct 6 volt coils wired in series. The
PVL coils have been found to work well. An alternative is the single 12
volt coil with dual outputs but the coil resistance must match the
Boyer’s requirements. To avoid the slipping of the magnetic trigger
rotor (and effecting the ignition timing) the rotor hold down bolt
should have a flat washer and a spring type lock washer installed on
it. The threads of the hold down bolt for the ignition rotor should
also be Blue LockTited but not until the system is strobe timed to the
verified timing marks as per the Boyer instructions. Be careful to not
install lamps in the system that exceed the wattage as originally
supplied, as the alternator output is very limited. Excessive power
draw will eventually run the battery down as the alternator will not be
able to keep the battery fully charged. Old alternator stators can have
internal shorts or broken wires and the rotor can have lost its
magnetism. The ideal is to replace an un-encapsulated alternator stator
with an encapsulated new one. The rotor magnetism should be verified.
A simple test that is very gross is that the rotor should be able to
support itself when allowed to hang freely from a steel plate bigger
than the rotor.

The Carburetion:
Amal carbs that were originally supplied had a few problems. Excessive
tightening of the carb flange nuts distorts the carb body making the
slides stick. Wear of the slide to the carb body (which is excessive
due to the nature of running two similar metal components against each
other and the resulting galling action) can cause the slide to stick.
Sticking slides is dangerous as a crash may be induced when you are
unable to stop the bike. And the needle jet and needle tend to wear
excessively to the point that the needle jet hole becomes oval. This
affects the air/fuel ratio and the performance of the bike. While old
Amals can be resurrected with slide bore chrome or brass sleeving,
distortion correcting bending of the carb body, and cleaning the small
passages, the best thing to do is to start with a new Amal. Be careful
to not over tighten the carb body flange nuts (use the rubber o-ring to
seal the carb to manifold junction and the carb should be able to be
rotated ever so slightly on the mounting studs). Also always drain the
carbs of fuel and insure that you have good petcocks on the gas tank.
Storing gas in the float bowls for more than a week has been known to
clog the pilot jet passages especially if the petcocks leak through
their closed position.

Vintage Brit Motorcycle Restoration,
Part 3-Chassis

A nice paint job on the chassis parts always makes the bike. The tank
should be done by a professional to get back to the original look with
two-tone color schemes that match the original ones. But this is your
bike and if you want a different paint scheme go for it! Make sure that
a gas resistant clear overcoat is used and that any decals or pin
stripping on the parts are added before the clear coat so that they
will be protected. Powder coating of the frame always looks great and
is usually very durable. Re-chroming bits and piece, while expensive,
makes the difference between “re-done” and “looks like new”. For the
controls new Amal style controls are available. I prefer the Gunnar
Gasser throttles even though they are not “correct”, but I ride my
bikes. Replacement handle bars in the correct bends are available but
if you have your favorite bend use it as comfort is more important than
“right”. The control cables can be ordered from your Brit dealer but I
have mine custom made by TerryCable who is local to me. When
reinstalling the motor in the frame be sure to clean away the powder
coating on the frame where the engine touches it in order to get good
electrical grounding of the engine and to avoid the paint breaking up
under the mounting points and the engine mounting hardware loosening.

The rims and wheels might be able to be cleaned up but new stainless
spokes and nipples along with new rims (plated steel, stainless steel,
or aluminum) and a freshly polished up hub (or freshly painted hub) can
make the bike. I suggest that if you are so inclined lace the wheels
yourself but I would suggest a professional truing job, at least. Be
sure to turn the drums if the wheels are apart and arc the shoes in
order to get maximum braking effect. The seat can be recovered (nothing
looks worse than a torn or faded seat on an otherwise nicely done Brit
bike). For tires choose vintage correct tires (Dunlop makes at least
two choices). The real Dunlops work better than the off brand copies.
While some Brit bikes have sufficient room to allow o-ring chains (far
superior to regular chains for longevity) some don’t. Check it out
before buying the chain. The original forks should be rebuilt as well
and repainted as necessary. The seals and bushes should be replaced and
good fork oil used.

When all of the above suggestions are taken I think you will find that
your Vintage Brit bike will be as reliable as if it were new, or at
least nearly so. But don’t be surprised if your investment exceeds the
value of the bike. Don’t do it this way unless you intend to keep the
bike forever, or nearly forever.