The patent numbers you will find on the triangular plate on the timing cover and in period brochures refer to several Triumph features by now standard across the range. The T21 was designed from the outset as a machine incorporating for then; modern features and aimed to attract new buyers looking for clean inexpensive transport. The design brief was for a clean, high performance, cc roadster and the components and specifications applied reflect this.
A bolted on sub frame supports the seat and rear suspension while additional welded on brackets are provided for other components. The headset and engine bridge support are malleable-iron castings. For this early frame the Trail is The forks are oil damped of conventional Triumph design for the period featuring chromed stanchions held in malleable cast iron brackets with the sliders supported by sintered bronze bushes.
The long internal springs and damping control are housed within the stanchions. Externally there are painted covers. The lower sliders feature cast clamps and at the lower end is a mudguard support that can be hinged down to support the front wheel to assist in wheel removal.
The recommended quantity of SAE 30 Oil for each fork leg is cc. The headset is enclosed by the trademark Triumph Nacelle, made in two parts with chrome trims disguising the joins, the Nacelle houses the headlamp with pilot light, combined ignition and lighting switch on the right, ammeter on the left, the speedometer and the horn. The steering damper knob is also mounted on the Nacelle. Shaped Rubber grommets are used where the handlebars pass into the nacelle and these additionally support the control cables and wiring.
The steering stops are associated with the lower fork bridge and there is a facility to lock the steering with a padlock. This type of adjuster slides easily within the lever clamp and has a knurled adjuster turning half a turn at a time to change the cable tension. The Throttle on the right is the Doherty pattern and features a curved a sleeve so that the cable enters the nacelle smoothly, the throttle friction clutch is operated by a small adjusting knob.
The grips are similar to the Amal Pattern, Black, quite thin with a fine raised finish and embossed with the Triumph Logo. The Speedometer is the Mph Smiths Chronometric with the trip meter operated by an extension accessible within the Nacelle.
Look carefully on the reverse for the date code applied to all Lucas components. The engine for the T21 was totally new, the first Triumph engine to feature unit construction with the gearbox housing as part of the right hand crankcase casting. The design allows the gearbox to be dismantled without disturbing the remainder of the engine.
The cc capacity is achieved with a bore of Within the crankshaft is the removable sludge trap designed to assist in the filtration of the engine oil by separating out particles by the centrifugal action of the crankshaft.
Oil is fed to the big end bearings through drillings associated with the sludge trap. On the left of the crank is the single row ball drive side bearing Hoffmann Metric while on the right is a VP3 Copper Lead bearing bush which is perforated so as to provide pressurised oil to the rotating crankshaft. From H the Timing side Crank Journal is heat treated and ground. The connecting rods are steel stampings, split to hold the white metal thin wall big end bearings and fixed with special high tensile blind bolts and lock nuts.
The small ends are pressed in phosphor bronze bushes. The engine is quoted as producing The finned iron barrels are painted in silver heat resistant finish see notes and attached at their base by 8 short specialised studs and nuts.
Between the barrels fore and aft are found the chromed push rod tubes which contain short pushrods operating on paired tappets; housed within removable blocks in the cylinder base. The pushrod tubes are sealed with specialised silicone rubber washers at either end. The well-designed light alloy cylinder head is fixed by 8 specialised bolts, four of which pass through the rocker boxes; these have paired rockers moving on hollow hardened shafts. The rockers feature drillings to allow oil to be fed to the adjustable tappets, these adjusters are assessed by removable caps on the rocker boxes.
Above the rocker boxes, is the branched oil feed pipe, oil is provided to the rocker shafts via drillings within each box. Each pipe is attached by a shouldered bolt running through the box and sealed with soft copper washers. The nuts associated with the oil ways are domed and cadmium plated. Early Cylinder Heads appear to have smaller exhaust ports and stubs than later heads look for the casting number to identify an early example.
The paired case hardened nickel steel camshafts run in plain bronze collapsible bushes on the left and un-bushed within the right hand crankcase, oil scrolls assist lubrication. The Inlet camshaft additionally operates the paired plunger oil pumps, the distributor drive and the timed breather system. The camshafts are located with steel plates and screws, punched on assembly so as to prevent them loosening. The camshafts are keyed to the timing pinions. The paired oil pump feeds pressurised oil via drillings to the oil pressure relief valve located in the front of the crankcase.
This features a Tell-Tail plunger to indicate the presence of oil pressure. From the relief valve drillings take the oil to the Timing Side crankshaft bush.
Oil having made its way from the crankshaft to the small sump within the crankcase is collected by the return pump via a filter gauze and curved pipe fixed within the right hand crankcase casting to be returned to the oil tank.
The filter here is accessed via a removable cap forward underneath the engine. The hub is fixed to the gearbox main shaft by a taper and located with a woodruff key. The clutch features 4 bonded and 4 plain plates. The clutch hub also incorporates a rubber shock absorber. Within the primary drive case is also located the Lucas three wire Alternator, the rotor keyed to the crankshaft and secured with a shouldered nut and locking washer.
Access to the final drive sprocket is via a removable plate with oil seal behind the clutch basket. The small attachment screws are punched to prevent them coming loose. The parts book indicates that there is a chain oiler jet but this is not illustrated and for these early machines the primary cover does not have the arrangement for tensioning or adjusting the chain.
The Clutch operating mechanism is by a quick thread screw; the cable enters the gearbox via a simple grommet on the top of the outer cover and connects directly to the clutch release lever within the gearbox.
Replacing the cable requires removal of the entire outer cover and extracting the cable through the rubber cover of the distributor as well. The four-speed gearbox features plain bushes for the lay shaft and ball bearings for the main, the gears are built up onto an intermediate cover while the outer cover contains the positive stop mechanism and clutch release screw.
A useful gear indicator is provided attached to the selector quadrant. The gears are down for down arrangement and selected to make the most of the power available. The Gearbox sprocket has 18 Teeth. The Engine Gearbox unit is held in the frame by shaped plates forward, the fasteners here are studs with distinctive dome headed nuts, while underneath, behind and above the gearbox are spacers and plates fixed by studs with conventional nuts.
The Carburettor is an Amal Monoblock, there is no choke arrangement though the carb features the usual tickler arrangement and receives its air via a rubber hose from an oblong air filter attached forward on the left of vertical main frame rail. The twin exhausts are 1 inch in diameter and terminate into the Triumph style of tubular silencer this does not show the offset entry of later silencers.
The silencers are attached to the frame by short lengths of tubing with trapped ends. The same support is used to attach the pillion footrests if these optional extras are fitted.
Recent documentation I have seen indicates that Triumph Silencers were made by Burgess one of the many Birmingham companies supplying the British Motor industry. This machine does not represent normal production specification and several details lead me to believe that this is a display machine to stimulate sales to the Police. The Distributor located behind the right hand cylinder is the Lucas 18D2 Unit; reference , driven by a skew gear from the inlet camshaft and is neatly covered and protected from the elements by a large rubber sleeve.
The ignition timing is adjusted by loosening a clamp located on the crankcase. The wheels are 17 inch, Dunlop WM2 Chrome rims 3. Ribbed in the pattern of the modern Avon Speedmaster, while the Rear is a 3. New for is the full width front hub, painted silver with a 7inch lightly polished alloy brake plate on the right and a shaped chromed hub on the left showing pressed concentric circles. The brake shoes fitted are not fully floating at this point in production while the cable stop fits on the lower fork.
The brake cable is additionally supported to the mudguard by a small P bracket. The rear wheel features the common hub from the other Triumph models; there is a combined tubular brake torque stay and lower chain guard. Like the front brake the rear brake shoes are not fully floating. A single piece upper Chainguard attaches to the left side of the swing arm using a specialised fastening at the rear and can swing up to assist wheel and or chain removal once this fastening is loose.
Both sides of the rear axle show shaped spacers and have the effective Triumph type chain adjuster, all parts cadmium plated. It is quite normal for the left adjuster to foul the brake plate when set to the minimum chain length.
The Brake rod adjuster is simple in form, T shaped and cadmium plated or chrome plated. Extended length is The Lucas Brake light switch, new for is the 6SA unit and operates by movement of a small ear on the brake lever, the switch itself attached to the brake torque stay nearby. The cables to the switch pass through a moulded rubber cover. The ribbed and flanged front mudguard is the full Roman Helmet style and is attached to the lower fork sliders by a shaped brace; the lower mudguard stay loops within the mudguard and when released by a single nut is able to act as a stand to help with wheel removal.
On the mudguard is fitted the front number plate fitted within a stylish chrome surround Patented. The rear mudguard is hidden by the bathtub enclosure, which is a new Triumph feature for The Bathtub enclosure is made from two 22 gauge steel pressings bolted together with a rubber strip between them. The bolts are carefully hidden so that the finish is neat.
The panels are supported by the seat loop and fastened by four self-tapping screws around the seat loop together with additional brackets associated with the fuel tank mount. Hidden underneath is a support stay running from the suspension mounts to a point at the rear of the panels. The stay rarely survives and many restored machines omit this feature in error. It is not illustrated or mentioned in the parts book! The rear number plate is attached by two nuts and bolts at the lower edge, the single upper mounting fits neatly between the Bathtub panels and no fixing is visible from the top.
Fitted are the chrome styling strips on either side of the Mouth Organ type Tank badge. There are Black rubber knee grips featuring the Triumph motif and are attached by two screws on either side. The Parts Catalogue has an illustration of an early machine and tank within the preface but the Petrol tank shown later is the later version.
The fuel tap is the Ewarts type with separate plungers for main and reserve leading to a single clear plastic fuel pipe connecting to the carburettor All early machines do not feature the Parcel Grid and I am trying to ascertain if this is fitted to any machines.
The Oil Tank is hidden behind the Bathtub Panels suspended at the top by two flat steel strips bridging the frame, additionally there is a lower mount associated with the rear engine plate.