Posted by: nativeiowan | November 16, 2014

Mike’s Bikes… 1952 Thunderbird

A bit of a history lesson to be had here…

1952 TRIUMPH THUNDERBIRD

tbd 1 copy

tbd 2 copy

This 1952 Triumph Thunderbird is similar to the 1950 T-Bird ridden by Marlon Brando in the 1953 film “The Wild One”, but his was black. This was a huge shot-in-the-arm for Triumph Motorcycles. To capitalize on it, they would come out with an all black 6T Thunderbird called the Triumph Blackbird.

All Triumph Thunderbirds were known by the model designation “6T”, referencing the 650cc engine displacement, as opposed to the Triumph Trophy 5T’s 500cc’s, and the “T” standing for Triumph, of course. The 1952 Triumph Thunderbird saw a switch from an Amal Monobloc carburetor to an SU Type MC2 carb in the interest of better fuel economy. This setup suited the 650 twin well & remained in service this way until 1959. The new SU carb required a new intake manifold. And a large forged steel lug was brazed into the vertical frame pedestal (behind the carburetor) that incorporated a round ‘eye’ through it running front-to-back to allow a connection between the single carburetor & the new Vokes D-shaped air filter. This “hole-in-the-frame” is a trademark of all 1952-58 Triumph Thunderbirds & is a way that collectors quickly identify a 6T frame.

The headlight nacelle & fork covers were enlarged on the 1952 Triumph Thunderbird to accommodate a new 7-inch pre-focused block-type Lucas MCF700 headlamp with an attractive underslung pilot light attached to the fork covers. The tank now had a central welded seam, there was a new oil tank & the D-type air filter, accessible only after removing the battery & battery box.

Rear brake drum & sprocket were now integral on the 1952 Triumph Thunderbird, rather than bolted on, as before. Internal changes were made to the gearbox. A color-coded Lucas electrical harness was adopted for the first time & changed everything over from negative-ground to positive-ground, an English quirk that persisted well into the late 1970’s.

This beautiful 1952 Triumph Thunderbird is made even more so by the stunning red paint job. Designer Edward Turner had an eye not only for engine design, but also for aesthetic appeal & marketing. The colors would start getting brighter & brighter as the 1950’s progressed, this 1952 Triumph Thunderbird being an early example. Of course, this trend was being led by the US auto industry in the height of the “Big Fin & Chrome Trim”-era where wild 3-tone paintjobs became common. And it all worked brilliantly, as new brightly-colored cars & motorcycles flew out of showrooms.

1952 Triumph 6T Thunderbird SPECIFICATIONS:

MODEL DESIGNATIONS:
1952 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:
Magneto Point Gap……………………….. 0.3mm / 0.120″
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
 

 

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