CHOKE LEVERS. DUAL CHOKE LEVERS, 1000 c.c. - PR17

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1 CHOKE LEVERS Choke levers of Amal manufacture were fitted to the majority of British motorcycles in the forties and fifties, including, of course, all Vincents. Most component parts were made of solid brass, a pleasant if rather heavy material seldom used nowadays on motorcycles. The finish was chromium plating with the visible brass parts polished before plating. The precise shape of the levers varies slightly, depending on the way fettling and polishing of the castings was carried out, but the end knob is always approximately 7/16 in. diameter. The retaining clip is invariably a chromium plated steel pressing, usually stamped AMAL. It was also used to retain the clutch and brake levers on all post-war Vincents with the possible exception of a few very early Series B twins, allegedly fitted with long, cast brass levers, probably of pre-war design and manufacture. It seems this AMAL clip is rare and some present-day owners have never had a chance to look at one; hence the photograph which hopefully will prove of some interest. The reason for the scarcity may seem evident: forty years have passed since the last Vincent left Stevenage and AMAL also stopped making control levers not long afterwards. During these four decades there was no doubt often need, and certainly ample opportunity, to renew damaged or tatty control levers. Some riders favoured expensive light alloy levers, but the majority were satisfied with chromium-plated proprietary replicas of the original Amal levers. These were widely available and they were also cheaper, although the finish and detail work was often mediocre. The clips were similar to the original article, but naturally lacked the AMAL letters; at the time this would have been ignored by most owners, if indeed they had noticed it in the first place. Moreover, these letters were heavily stamped and formed relatively deep crevices, where dirt and moisture remained trapped, providing excellent conditions for the growth of rust and subsequent lifting of the chromium plate. The rusty clip would then be thrown away by the disgruntled owner, to be replaced by a plain replica possibly less prone to self destruction. The AMAL clip (or its plain replica) features 15/64 in. dia. holes 1.5/16 in. between centres. It is not interchangeable with the BOWDEN clip (1.3/8 in. between centres) fitted to the majority of exhaust lifter levers. The steel screws were 1 B.A. with a shallow domed head, originally cadmium plated (see drawing). At least one authentic variation of this screw exists with a smaller (0.300 in. dia.) head, similarly shaped. Original screws in good condition are very rare indeed. Although the screw is strong enough (just... ), the small slotted head was easily butchered by an ill-fitting screwdriver. Fortunately, good stainless steel replicas are now available from some Vincent stockists. The drawings are intended to help riders who wish to make replicas of missing or damaged parts, most of which are not too difficult to copy, if the will is really there... They may also assist buyers at jumble sales where incomplete or mangled assemblies are often hard to identify when the original appearance and precise dimensions are not known. DUAL CHOKE LEVERS, 1000 c.c. - PR17 The 1000 c.c. dual choke lever is not really an obscure component, but it is a rare one, difficult to find, even in poor condition or incomplete. The reason for this scarcity is simply that only a few British motorcycles of the era were equipped with

2 two carburettors blessed with separate choke levers, which, incidentally, can be a real advantage for those living at high altitudes. Moreover, although this Amal component was soundly designed and made, the relatively complex assembly can easily be damaged in the wrong hands as the fine threads used to control the levers movement do not tolerate hamfisted adjustment. Assuming the component has been completely dismantled for cleaning or replating, etc., the sequence of re-assembly is as follows: 1) Slip on the 1/2 in. i.d. spring steel washer, well greased beforehand (do not use Graphogen or Molyslip which are apt to be messy on gloves afterwards); 2) then the long lever; 3) the eccentric lever pivot plate (threaded 11/16 in. x 32 t.p.i.); 4) the 11/16 in. i.d. spring steel washer, again well greased; 5) the short lever; 6) thread on the slotted bronze nut and adjust it (details further on); 7) fit the steel locking plate; 8) place the thin chromium plated brass cover plate on the top; 9) screw in the chromium plated 5/16 in. B.S.Cy. setscrew (no washer), and adjust as explained further on; 10) re-fit the cables, the short lever normally controls the air slide on the front carburettor. Adjustment of the castellated bronze nut which controls the movement of the short, top lever is done with a 1/2 in. B.S.F. spanner (0.820 in. A/F) preferably a box spanner (there was one in the original tool kit.. ) to avoid possible damage to the hexagon edges. Do not overtighten, the fine threads are easily and irreparably damaged; adjustment is correct when the lever can be moved with two fingers but shows no sign of moving on its own accord when underway. The locking plate is essential; without it the nut will tend to move in unison with the lever and will inevitably loosen. It may be necessary, of course, to turn the nut a few degrees to align the plate with the nearest slot. The plate is purposely a tight fit on the central pivot square and the nut slot. Tap it carefully into position, avoiding undue force. Likewise, the central chromium plated 5/16 in. B.S.Cy. screw which controls the long, bottom lever should not be overtightened, the aim being again to ensure easy yet firm operation of the lever. An adjustable spanner is likely to be needed as normal imperial spanners do not fit the unusual in. A/F hexagon size. The reason for this odd dimension is not evident. Perhaps it was preferred to in. A/F (normal hex. size for a 5/16 in. screw) and to in. A/F, the next size up, because it offered more support to the thin cover plate, and also looked better. Possibly the makers wisely wished to discourage unnecessary fiddling; once the adjustment is correct, it never needs to be disturbed as the cables are readily removed or replaced without dismantling anything whatever. Apart from missing or badly damaged parts which, hopefully, can be copied on a lathe, one occasionally comes across a main body where the central pivot is beyond repair. This can be made good as follows: saw off the damaged pivot and dress the stump flush with the base of the body with a smooth file. Take a short length of 1/2 in. diameter steel or bronze rod and machine a copy of the pivot shown on the drawing of the main body (9/16 in. long, threaded 5/16 in. B.S.Cy. right through). Fix this pivot to the main body with a short stud, made from a 5/16 B.S.Cy. bolt and screwed into the body which is usually threaded right

3 through. Leave enough room for the cover plate screw, and use Loctite to lock the body/stud/pivot into one unit. Properly done, the repair is better than new. SINGLE CHOKE LEVER, 500 c.c. - PR17/1 It would seem that more than one type of choke lever was originally fitted to the 500 c.c. models. The thread of the pressure plate screw is either 5/16 in. B.S.Cy or 5/16 B.S.F., whilst the head is normally hexagonal, in. A/F (as on the the dual lever version), or in. A/F. Likewise, at least two different (but interchangeable) pressure plates exist and there may be other variants. So far, we can only vouch for the Amal type and its minor variations described and drawn in this article which is based on choke levers from several Comets. It was certainly original equipment on most Comets. As might be expected, the style and finish of the component show a strong family likeness to the Amal dual lever version. The lever closely resembles the dual top lever and may have been cast in the same mould, but the pivot hole is a different size. As on the Twin its precise shape varies, depending on how vigorously the fettling and polishing were carried out prior to plating, but the end knob is also usually 7/16 in. diameter. The top plate, however, is completely different because it is designed to act as a pressure plate. It is therefore a rigid, chamfered disc, 3/16 in. thick in the centre, usually machined from a brass casting sometimes stamped AMAL, as shown on the drawing. The central hole is either as drawn, or 13/32 in. square (i.e. exactly like the hole in the lock plate used on the dual lever assembly). In either case, it engages with the square shoulder of the pivot on the main body so that the plate cannot rotate in unison with the lever. As we have seen, the pressure plate screw thread may be either 5/16 in. B.S.Cy or 5/16 B.S.F.; it is therefore essential when dealing with loose parts of unknown origin to check that the thread of the screw matches that of the pivot on the main body. However, a pivot with a stripped thread can be renewed as explained at the end of the section on the dual choke lever. Assembly is quite straight forward: 1) Slip on the 1/2 in I.D. spring steel washer, well greased beforehand (two washers may offer less critical adjustment and a better action; 2) then the lever; 3) engage the pressure plate on the squared top of the pivot, it may be a tight fit; 4) thread on the pressure plate screw (no washer); if it is in. A/F an adjustable spanner may required as explained earlier; 5) replace the cable.

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