1953 TRIUMPH THUNDERBIRD


Triumph Thunderbird, Triumph motorcycles, Triumph speed twin, Triumph Tiger 110

Sitting in for the 1953 Triumph Thunderbird is this lovely 1951 Triumph Thunderbird 6T. Very similar to the 1953 model, they share in common the rigid frame with sprung rear hub, forks, brakes, bodywork & cycle gear. Paint colors & minor trim features vary. Unfortunately, no photo was available at this time of a proper 1953 T-bird, so we had to make do with this. We need pictures of your bike to help round out our inventory. If you have a 1953 Triumph Thunderbird, please SEND PICTURES!




1953 TRIUMPH THUNDERBIRD - MODERN ELECTRICS
The 1953 Triumph Thunderbird benefited from the switch to alternator electrics, points & coils for ignition. Gone were the old magneto (spark) & dynamo (lights). The new electrics appeared first on the 500cc 5T, then began appearing on other models throughout the model year.

1953 TRIUMPH THUNDERBIRD - PRIMARY SIDE
The new Lucas RM12 alternator lived in the primary chaincase on the outer left end of the crankshaft. Changes to the primary cases were made to accomodate & a large, elegant bulge appeared on the outer primary case that would evolve into the lovely Triumph logo that would appear on later Unit Construction twins. The points were located in a distributor which occupied the space behind the cylinders where the magneto used to live, and was driven by the same method: gear-driven off the inlet cam gear.

1953 TRIUMPH THUNDERBIRD - NEW ELECTRICAL SYSTEM
The 1953 Triumph Thunderbird had no means of voltage regulation, just a simple full-wave, 2-plate rectifier under the seat for converting AC to DC current. In case of a dead battery, an "Emergency" switch brought the alternator's full output into the ignition circuit, making it easier to start. The old magnetos were self-sufficient & would start no matter what. These new-fangled alternators & coils were suspect in the eyes of the public. Engine mounting plates were modified to deal with the absence of the dynamo.

1953 TRIUMPH THUNDERBIRD - ENGINE SHOCK ABSORBER
One nice feature that pre-unit Triumph twins had prior to the alternator was a very neat engine shock absorber that occupied the place at the left end of the crank now taken by the new alternator. This shock absorber was really an ingenious contraption. It was comprised of two pieces cammed to one another with ramps & pushed together with a spring. One was hooked to the crank & the other to the primary engine sprocket. It allowed a certain amount of "give" in the form of some controlled slippage in both directions between the two pieces along their ramps, against the spring tension attempting to clamp them together. This served to quell engine vibrations so effectively that it made everything last longer: engine bearings, primary chain, gearbox, even the final drive chain were reputed to last longer due to the smoothing effect of the shock absorber. Unfortunately, this brilliant innovation had to be dumped to make room for the alternator. Attempts were made to accomplish the same task with a shock absorber inside the clutch hub, but nothing worked as well.

1953 TRIUMPH THUNDERBIRD - TEETHING PROBLEMS
The early alternator systems had problems. The distributor was inaccessible, the wiring much more complex. The only way to get full power out of the alternator was to turn on the headlights. This triggered the alternator to go from 4 stator windings to 6. The critical air gap between alternator rotor & stator was proving vulnerable to play in the bottom end. Many fixes were tried, but not until the resin-encased the stator in 1968 did the problem truly get solved. Loose primary chains would also eat into the alternator wiring.

1953 TRIUMPH THUNDERBIRD - DISTRIBUTOR GREMLINS
The distributor too was fraught with problems. It had one set of points & one coil, with a rotor & distributor cap, car-style. The small dimensions of the bushings also caused excessive wear.

1953 TRIUMPH THUNDERBIRD - NEW ELECTRICS
While there were some early problems with the new electrical system, for the most part, the change was progress. And the good thing about alternators & points was that, when they did fail, the were much less costly than replacing a magneto or dynamo. However, magnetos were retained on some pre-unit sport models, as racers preferred them & Triumph Motorcycles didn't want to lose their business to BSA or Norton, who were still offering the mag.

1953 TRIUMPH THUNDERBIRD - CARRYOVER
Otherwise, the 1953 Triumph Thunderbird was pretty much carried over from 1952. The same rigid frame & sprung rear hub that had been with us since the War were on their last year. 1954 would see the introduction, finally, of a proper swing arm rear suspension.

Triumph Thunderbird, Triumph motorcycles, Triumph Speed Twin, triumph Tiger t110

Again, standing in for the 1953 Triumph Thunderbird, this is a 1951 Triumph Thunderbird, as no photo was available of a 1953 Triumph Thunderbird. Here you can see the rigid frame & sprung rear hub.




MODEL DESIGNATIONS:
1953 Triumph Thunderbird 6T...................... Roadster

ENGINE:
Engine type....................................... OHV vertical twin
Horsepower at RPM............................ 34 BHP @ 6,500 rpm
Bore................................................ 71mm / 2.79"
Stroke............................................. 82mm / 3.23"
Displacement.................................... 649cc / 40 cu. in.
Compression Ratio
Home Market (UK).................................. 7.0:1
Export Market (US)................................ 8.5:1
Valve Clearance (cold):
Inlet................................................ 0.05mm / 0.002"
Exhaust............................................ 0.10mm / 0.004"
Valve Timing:
Inlet Valve Opens.............................. 34 degrees BTDC
Inlet Valve Closes.............................. 55 degrees BTDC
Exhaust Valve Opens.......................... 48 degrees BTDC
Exhaust Valve Closes.......................... 27 degrees BTDC

IGNITION:
Spark Plug Gap.................................. 0.50mm / 0.020"
Timing (fully advanced):
Crankshaft position............................. 39 degrees BTDC
Piston position................................... 11mm / 7/16" BTDC

CARBURETORS:
Type................................................ SU Type MC2

TRANSMISSION:
Speeds.............................................. 4
Gear Ratios:
4th - Top........................................... 4.88
3rd - Third......................................... 5.81
2nd - Second...................................... 8.25
1st - Bottom...................................... 11.9
RPM @ 10MHP in Top Gear................... 638 RPM

CLUTCH:
Type................................................ Multi-plate, wet
Number of Plates:
Drive Plates...................................... 6
Driven Plates.................................... 5
Friction Material................................ Cork

SPROCKETS:
Engine............................................. 24 teeth
Clutch............................................. 43 teeth
Gearbox.......................................... 18 teeth
Rear Wheel...................................... 46 teeth

CHAIN:
Primary, pitch.................................. 1/2" X .335" X 5/16"
Primary, length................................. 70 links
Final Drive, pitch............................... 5/8" X .400" X 3/8"
Final Drive, length............................. 101 links

CAPACITIES:
Fuel (US versions)............................. 3 Imp. gal.
Fuel (UK & export versions)................. 4 Imp. gal.
Oil Tank........................................... 5 pints / 3 L
Gearbox........................................... 2/3 pt / 400cc
Primary Chaincase............................. 1/4 pt / 150cc
Front Forks....................................... 1/4 pt / 150cc

TIRES:
Front............................................... 3.25 X 19"
Rear................................................ 3.50 X 19"

SUSPENSION:
Front............................................... Telescopic Forks
Rear................................................ Sprung Hub

BRAKES:
Front............................................... 8" / 10.32cm SLS
Rear................................................ 8" / 17.78cm SLS

DIMENSIONS:
Seat Height...................................... 31" / 77.5cm
Wheelbase........................................ 55.25" / 140.3cm
Length.............................................. 86.25" / 219cm
Width............................................... 28.5" / 72cm
Ground Clearance.............................. 5" / 12.7cm
Dry Weight, unladen............................ 370 lbs / 168kg


TRIUMPH MOTORCYCLE BOOKS


TRIUMPH BONNEVILLE YEAR-BY-YEAR

TRIUMPH BONNEVILLE ESSENTIAL BUYER’S GUIDE

COMPLETE BOOK OF CLASSIC & MODERN TRIUMPHS

TRIUMPH MOTORCYCLES 1956-1983

FACTORY-ORIGINAL TRIUMPH TWINS

TRIUMPH MOTORCYCLES

TRIUMPH MOTORCYCLE RESTORATION, PRE-UNIT

TALES OF TRIUMPHS & THE MERIDEN FACTORY

TRIUMPH ILLUSTRATED SHOP MANUAL, 1935-1939

TRIUMPH ILLUSTRATED SHOP MANUAL, 1937-1951

TRIUMPH ILLUSTRATED SHOP MANUAL, 1945-1955

Triumph Thunderbird
Triumph Thunderbird, Pre-Unit
Triumph Thunderbird, Unit Construction

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