1964 BSA Cyclone 500 - 4-Page Vintage Motorcycle Road Test Article

Description

1964 BSA Cyclone 500 - 4-Page Vintage Motorcycle Road Test Article
Original, Vintage Magazine article
Page Size: Approx. 8" x 11" (21 cm x 28 cm) each page
Condition: Good
Those who have raced bsa’s 500cc Gold Star single
(known affectionately around these offices as the
“BSA Roto Rooter”) will offer the opinion that any re-
placement would have to be awfully good. Well gang,
BSA has a replacement and it is awfully good. They have
the Cyclone 500 twin for you scrambles racers, and it
has all the sturdiness and thunderous power that made
the old single a winner. The diehards will say that there
is no substitute for the single, and they may be right; but
in the long run the twin will have the last word.
The reasons for this are manifold, but basically the
twin has the advantage because it will turn faster, and
higher engine speed inevitably means more power. This
maxim is particularly true when the twin in question is a
good one, as the BSA certainly is. In overall layout, the
BSA twin is very modern, with nearly equal bore and
stroke (65.5mm x 74mm; really should be the other
way around) and a unit crank/transmission case. The
crank runs in two mainbearings — one plain; the other
ball — and plain inserts at the rod journals. The plain
bearing is used at the timing end of the crankshaft pri-
marily because that arrangement offers a simple means
of feeding oil to the passage that carries lubricant out to
the rods. A double-gear pump inside the timing cover
supplies pressure to the bearings and scavenges the sump,
returning oil to the reservoir tank located under the seat.
Unlike another popular British twin, which has a
pair of camshafts, the BSA has a single cam, mounted
high in the crankcase behind the cylinders. The cam fol-
lowers are carried in bores machined into the cast iron
cylinder block, which is rather a neat way of doing things,
and the pushrods pass up through a chest cast into the
block and cylinder head. Incidentally, in these late BSA
twins, the flange at the base of the cylinder block, where
the block is bolted to the crankcase, has been strengthened
and that stiffens both the block and the crankcase.
Removing a single cover exposes all of the upper
valve gear in the BSA engine, and there is enough room
under the fuel tank to permit removal of this cover and
adjustment of the valves. Take a peek in there and you
will see that the rocker shafts are carried in posts cast
integral with the head. This provides a good, solid mount-
ing for the rockers and eliminates flexing — which can
have a surprisingly upsetting effect on valve timing at
high speeds.
Like other BSA twins we have tested, the Cyclone
500 was very smooth and easy to start. The twin carbu-
retors appear to affect low speed tractabiiity not at all,
but it is impossible to state this as an absolute fact. The
engine has a cam that gives rather racey valve timing, and
it has to be up “on the cam" before it begins to run clean
and develop any power. Once it does begin to chum at
the proper rate, which is at a relatively low engine speed,
there is a lot of power on tap and it does not trail away
much until the engine gets right up to the threshold of
valve float. At any point between burble (about 2000
rpm) and valve float (about 7500 rpm) it runs strong
and clean. In accord with their long standing policy, the
makers give no figures on power output, but on the basis
of the machine’s performance we would judge the output...
11596-6410-08