Parts

Mudguards

From 1937 there were four types of mudguard of which three fitted the heavyweight range. Front and rear mudguards came in two widths. As a general rule the wider, 6'' guard was fitted to the deluxe models, while the narrower 5'' guards went on the Tiger models. The Speed Twin tended to be fitted with a combination, 6” rear and 5” front which looked right. At that time narrow mudguards and high pipes were regarded as sporty. In addition, there was an optional valanced mudguard which was the big 6” guard with extra side-panels welded on. The customer could have any combination of these but the catalogue illustrations presumably represent the factory recommendations and therefore probably the majority. The new beaded front number-plate in 1939 meant a change to the fitting on the front mudguard

Post-war it became more simple. The earlier 6” rear mudguard continued and a new front for the tele fork but still with the rivetted stays In 1948 new front and rear mudguards. The rear now split under the saddle for a neater appearance although not so easy to remove the rear wheel. The front guard now has the detachable stays and distinctive raised rib around the nose. Around 1950 there was a new pressing for the front guard (see pic left). There was a valanced front mudguard appearing in the fifties as an option.

Gearboxes

There were two main types of gearbox during the years 1937-1953. The first condition pre-unit box was more or less the same from 1937-1948. There were differences in the castings on the pre-war box to the main case and outer cover but only cosmetic. Post-war a different main shaft second gear and mainshaft high gear were used from 1946 and must be fitted as a pair. Tapped lugs for the speedo drive appeared in 1947 (from TF19577) as the sprung hub was an option. In addition other parts were modified like the kick-start ratchet/pawl but they are all interchangeable.

For 1950 a new stronger box for the 650cc engine was introduced and very few parts are interchangeable between the two gearboxes. Dimensionally all rigid frame gearboxes are the same and will work across all models as the mountings are identical, which is useful. Pre-unit Triumphs always used the same gearbox across the whole range within each year. The only exception being wide-ratio gear sets fitted to TR5 and TRW. These should be stamped WR on top.

Headlamps

Pre war, Triumph fitted the Lucas D142, 8'' headlight to all instrument panel models. Usually with the flat, vertically fluted glass. The rim had a rolled front edge and a long curved flat clip with a rolled front edge to retain it. The clip is retained in the shell with a straight length of wire. During the 1938 season Triumph also used a domed glass headlamp as supplies from Lucas allowed. This rim was retained with a 'two finger' chromed, cast alloy clasp which relied on a 'W' clip retained in the shell. The shells are therefore not interchangeable, differing in the clip retaining arrangement & cutout underneath. In addition, both versions came in two different materials: The chrome shells on Tigers and Speed Twin were brass whereas the painted shells on the Deluxe range (5H/6S) were steel. The steel shells seemed to have survived better as the brass becomes brittle and splits. The correct lengths for the headlamp struts on the '37/'38 models are 4'' at top, 7'' bottom, between centres. However, the new number-plate for 1939 seems to have needed a longer lower strut at 7 1/2'' to clear the headlamp.

Primary chaincases

For 1937, the heavyweight inner primary case was very similar to the previous (1936) year, and the two are interchangeable differing only in detail including a breather and the oil sealing arrangement around the gearbox main shaft. In addition, the earlier version is of a heavier construction. The outer primary too was basically the same casting as the '36 models but with some of the detailing tidied up. The most obvious identifying point for these early (1936/37) outer primaries is the round-boss fairing over the shock absorber assembly. For 1938 a new outer appeared with a teardrop shaped boss at the front. Unfortunately, casting numbers tended to remain the same on different cases, and so cannot always be used for identification although the outer cover is the same for singles and twins. A new inner cover appeared in 1938 for the twin cylinder engine without the shaped distance piece over the top front and remained the same until the post-war era. For 1939 the outer cover gained a tapered screw adjustor for oiling the final drive chain. All pre-war outer primaries had a hexagon headed oil level plug under the footrest. The lightweights used a shorter case and so the two (heavy/light) are not interchangeable. It is useful to know that the pre-war lightweight outer will fit post-war 3T and also the TR5 later on.

Post-war the same primaries continued although the level pluq was deleted. However the casting is the same and it’s easy to drill and tap a level plug if you want to use post-war cases on a pre-war bike and retain the original look. The 3T used a unique inner as did the TR5, neither of which will fit anything else. In 1953 alternator ignition meant that the 5T used a completely new set of primaries.

Petrol Tanks

In 1937 and 1938 all heavyweight models used the same tank, a three and a quarter gallon tank easily recognised by the asymmetrical concave recess underneath, to make room for the 500cc single valve gear. Only one small change occurred, the addition of tank badge screws for 1938. 1937 models having decals (transfers) for the badges. The lightweights used a very similar sized tank but a subtly different shape. Also the mounting points are different so they can’t really be switched. Instrument tanks were chrome-plated with three painted panels. The factory offered a tank reconditioning service for damaged tanks which included a budget version that was all painted with no chrome.

For 1939 the T100 had the larger four gallon tank and the two tanks are not really interchangeable as fitting the four gallon tank to a TH frame will result in the forks hitting the tank on full lock. This is due to design changes around the steering head. For 1940 all heavyweight models got the new TF frame and the Speed Twin got the larger tank as well. The 1940 6S seems to have retained the smaller tank. Tank badges changed again in '39 from brass in '38 to a diecast alloy as per the post-war type. The new larger tank also had twin taps which obviated the need for the annoying balance pipe at the front on the earlier tank.

Post-war the same tank appeared on the two 500cc bikes and the 3T got the tank from the pre-war lightweights. This arrangement lasted until 1949 when the instrument panel tank disappeared forever. For 1949 a new tank with tapped lugs for the parcel grid where the instrument panel was before and the same side hinged butterfly filler cap. Also an entirely new tank for the 3T which may have used pressings from an earlier WD tank. In 1950 different finishes but the same tanks, now for three models including the 650. Also a new tank for the TR5. 1951 saw the more modern push and twist filler. For 1952 a different construction with the tank formed from two halves joined together with an unsightly seam down the centre. No change for 1953.

Instrument panels

The first diamond shaped instrument panels appeared in 1937 with the restyled range announced for that year, although the latter half of 1936 saw an early introduction of some of the features from the new range. The panel itself was of steel construction and chrome plated. The Lucas 3 position lighting switch with bakelite top and chrome surround was used which was to remain the same until the post-war era. The Lucas 0-4-8 ammeter with chrome case and sprung mounted fitting was distinguished by four pips around its base to locate the serrated ring used to compress the spring mounting. In addition, a single pip under the bezel located the gauge correctly in to the panel. The oil pressure gauge was of Eureka manufacture, printed with the Triumph logo and rated at 25 lbs for all models. The needle was a distinctive design with a crescent on the tail and the movement pivoted in the centre of the dial. The inspection lamp was a Lucas DC 40 brass lamp with four holes around the edge of the base, two of which located onto two sprung loaded pins fixed to the lamp housing, which was spot-welded to the panel.

The following year, 1938, saw the introduction of the twin cylinder model and a new material of black bakelite for the panel (advertised as being anti-dazzle). This panel requires a stout, pre-formed rubber mounting to sit correctly on the tank, while the steel panel simply requires a rubber bead pressed over the underneath edge. The screw securing the new panel had a reduced diameter head in order to recess into the panel. The light switch and ammeter remained unchanged but a new 100lb oil gauge, of the same design and manufacture, was introduced for the twin because of the increased oil pressure necessary for the crankshaft construction. The singles in the range continued with the same 25lb gauge. The new material for the panel necessitated an inspection lamp fitting which was fastened with three small screws to the panel. In addition, a second type of fitting for the lamp was employed which consisted of a bayonet fastener involving two small pins on the lamp engaging two slots in the holder against a sprung washer. Both this type of fitting and the previous sprung pins type appeared apparently at random over the year and perhaps appeared occasionally in to the next season.

1939 models retained the bakelite panel and saw the introduction of a new oil pressure gauge rated at 160lbs, probably for the T100 model, but fitted to both twins. Again, switch and ammeter remained the same, but a new Lucas DC44 inspection lamp appeared. This lamp seems to have exclusively used the bayonet type fitting and consisted of a bulb-holder which pointed upward leaving the bulb above the panel, protected by a hood with a domed top and a window at the rear to allow the light to shine on the instruments.

For 1940, the steel panel was re-introduced, probably because of constant breakage of the bakelite unit. If not fitted with the thick rubber gasket in good condition, constant rattling of the thing must have driven owners to over-tighten the holding screw. The finish of the new panel differed however from 1937 in that it was painted in a black 'crinkle-finish' paint. It seems likely that the DC40 inspection lamp was re-introduced for 1940 after criticism of glare from the DC44 light, which was not switched, and was therefore constantly on when the lights were switched on.

Post-war, the same panel continued. The ammeter now gained four locating pips under the bezel for more positive location, resulting in four corresponding cutouts in the panel. The Lucas DC40 inspection lamp seemed to continue for early post-war models but changed to a completely new bakelite construction in 1946 and used exclusively the bayonet fitting. Again, the light switch remained the same but the oil gauge was now of a different design. The needle was pivoted at the bottom and was straight with no decoration. The gauge was rated at 100lbs, for what had become an entirely twin-cylinder range. The Triumph logo was still printed on the face, but without the dire warnings of the consequences of running too low an oil pressure printed in red alongside. According to Harry Woolridge, dealers and the works were constantly hearing from worried owners experiencing apparently low oil pressure and it was for this reason as much as anything that the gauge was deleted altogether for the new look in 1949.

Girder Forks

In 1939 the girder fork was modified to fit the new TF frame. The TF headstock was mounted at a steeper angle and so the forks used a shorter lower link to increase the trail. The TH frame used 105mm (between centres) lower links on the girder fork whereas the TF frame lower links were 100mm. The effect of fitting the longer (TH) lower link to a TF frame is to produce an alarming high speed wobble. In addition, the TF girder used a different top crown (also referred to as ‘head clip’ in the parts book). The T100 top crown/head clip had a deeper cast lug for the spring top retaining bolt making it stronger. Quite possibly it also had other more subtle differences so should not really be substituted by the TH version. The TF girder was then used on all heavyweights in 1940 and according to the catalogue, check springs were added, although the introduction of these (involving a new lower link with a pin for the spring) seems to have been patchy. This mod also necessitated a different headlamp mounting strut arrangement.