1966 Triumph TR6
1966 TRIUMPH TR6 BY THE NUMBERS
For the 1966 model year, the model lineup were TR6, TR6R, TR6SR, TR6SS, TR6C & TR6SC, all called “Trophy”. Engine & Frame Numbers ran from DU24876 to DU43161, with build dates running from August 6, 1965 to July 8, 1966. The TR6C was essentially a standard 1966 Triuymph TR6 with wide-ratio gearbox, slimmer 2.3-gallon tank & Dunlop Trials Universal tires (tyres). The TR6SC was the same as the TR6C except for standard gear ratios, alloy mudguards (fenders) & a silenced exhaust. The TR6SR was basically a standard 1966 Triumph TR6 but with raised handlbars & a smaller capacity fuel tank. The prices new were around $1,200 USD.
Shorter “Red Spot” valve springs were installed with thicker bottom cups to ensure better valve control with less spring surge. A new central flywheel, lighter by 2-1/2 pounds, was fitted to the crankshaft, while maintaining the 85% balance factor. Crankshaft end float (lateral movement) control now reverted back to the timing side main bearing (having been moved for one year only, in 1965, to the drive side). This was accomplished by a clamping washer that was interposed between the timing pinion (gear) & the main bearing inner spool. And on a drive side, a heavier, load carrying single lipped roller bearing (#RM11L) replaced the old ball bearing.
Oil was now pressure-fed to the exhaust cam followers through drillways in the crankcase, barrels & exhaust tappet block. Starting with engine #DU42399 a dowel was placed at the joint between the crankcase & barrels to stem oil seepage. The new tappet blocks were made to fit new, redesigned pushrod tubes with better sealing top & bottom.
Starting with engine #DU42251, the 3/4″ radius cam follwers (tappets) were replaced by the now-famous “R-type” tappets of 1-1/8″ radius. The intake (inlet) valves were also increased in head diameter from 1-7/16″ to 1-19/32″, and the exhaust valves were enlarged to 1-7/16″, just like the Triumph Bonneville T120.
Starting with the 1966 Triumph TR6, the speedometer drive was moved from the layshaft in the gearbox to the rear wheel. The kickstart lever was made longer for easier starting. The final drive chain oiler at the rear of the primary case was eliminated. The adjusting screw on the clutch pressure plate was fattened to 3/8″ starting with #DU31820.
FRAME & RUNNING GEAR CHANGES
The 1966 Triumph TR6 featured a change in steering head angle from 65-degrees to 62-degrees to quicken steering & a fairing lug was added to the neck. A new battery-mounting system used rubber bushings running on pegs, instead of rigid mounts. The swingarm was widened by 1/4″ on the right side. A new fork stem & bottom lug tightened the turning radius. The rear sprocket went back to 46 teeth. A new, wider front brake drum increased brake swept area by 40%.
A new petrol (fuel) tank was slimmer & available in 3- or 4-gallon capacities. A new tank badge came with it, perhaps the most popular ever, the now-famous “eyebrow badge”, so-named for its large chromed ‘eyebrow’ above the “Triumph” logo (see photos). With the elimination of the rear chain oiler from the primary case, the oil tank was modified to accommodate, with an adjustable metering screw in the filler cap neck that controlled the amount of oil that was allowed to run down to the chain. Along with these mods, the top end oil line was now being fed off the top of the return pipe, rather than below the tank, as before. This led to weak & often erratic top end oiling which in turn caused premature rocker arm wear. A service kit was soon issued to reverse this.
NEW 12-VOLT ELECTRICS
Every 1966 Triumph TR6 (except the TR6C) got a 12-volt Zener Diode mounted to the battery box, as the whole system switched to 12 volts. Triumph Motorcycles opted for two Lucan SKZ9E 6-volt batteries hooked up in series to produce 12 volts. However, by #DU32985 they switched to a single Lucas PUZ5A 12-volt battery, with modified carrier to match. The 7-inch chromed headlight contained the ignition warning & high beam indicator lights (after #DU29247). The 12-volt Lucas MA12 coils were still located as before, although some US models got the smaller Siba 3200/1 coils. A Lucas 88SA light switch remained on the left-side cover as did a new ignition switch. The location of the Zener Diode had to be changed slightly due to overheating problems, starting with #DU40436.
1966 Triumph TR6 SPECIFICATIONS
Bore & Stroke
Off-road/street (dual purpose/enduro)
Air-cooled OHV vertical twin
649cc / 40.0 ci
71mm X 82mm / 2.79″ X 3.23″
1- Amal Monobloc, 1-1/8″
Battery & coil, Lucas
42 bhp @ 6500 rpm
3/8″ triplex chain X 84 links
Engine 29T X Clutch 58T
4-speed constant-mesh, right-foot shift
5/8″ X .400″ X 3/8″ chain X 106 links
Gearbox 19T X Rear 47T
Brazed lug, full-cradle, single downtube
Telescopic fork, hydraulic damping
Swing arm, 2 Girling dampers
8″ SLS drum, full-width
7″ SLS drum, one-side
3.25″ X 19″ Dunlop
4.00″ X 18″ Dunlop
2.5 Imp gal (US)/4 Imp gal (UK & export)
54.5″ / 140.3 cm
32.5″ / 77.5 cm
5.0″ / 12.7 cm
363 lbs / 165 kg