1978 TRIUMPH BONNEVILLE


1978 Triumph T140E Bonneville 750, Triumph motorcycles

1978 Triumph T140E Bonneville 750, Triumph motorcycles

This 1978 Triumph Bonneville is a T140V, which still has the Delta-style head with splayed intake ports & Amal Concentrics. Later 1978 Bonnevilles were T140E's, with parallel intake ports & MkII carbs. This color scheme was popular in 1978. A sign of the times: earthtones were in, even for motorcycles seats.


1978 Triumph T140E Bonneville 750, Triumph motorcycles 1978 Triumph T140E Bonneville 750, Triumph motorcycles SMOG DOG
The 1978 Triumph Bonneville got a late-year update by Triumph Motorcycles. After several years of little or no change, new U.S. emissions legislations affecting motorcycles was forcing the struggling Meriden Co-op to finally make some changes, although not the changes they would have like to make, to be sure. The 1978 model year started with Engine #HX00100, with the standard T140V Bonneville line continuing into 1978 pretty much as they had in 1977. However, on January 1, 1978, production began on its replacement: The T140E. The "E" stood for "Environmental" & meant that the once-mighty fire-breathing Triumph Bonneville was becoming a "smog dog".

ENGINE
All engine changes seemed to be aimed at meeting every more stringent US emissions guidelines, not performance anymore. The compression ratio was dropped to 7.9:1 in the US to match the UK and export markets, which helped emissions & standardized production.

NEW HEAD
UNF threads were still making their way through the engine & it finally got a composite head gasket in place of the prehistoric copper one. But the biggest change was just north of it. A new cylinder head was cast which now placed the intake ports in parallel paths aiming straight back, ending forever that time-honored Triumph Bonneville tradition of splayed carburetors. The new head also had revised combustion chambers & reworked valve guides & seats.

NEW CARBS
Again, emissions-driven, a new set of carburetors was installed, the 30mm Amal Concentric MkII, suddenly making the old standard Amal Concentric the Mk I. These new carbs were boxy-looking on the outside, but besides the elimination of the tickler valve, very little was different inside. An enrichening lever was located on the left carb that operated both units via a common linkage. The whole point was satisfying the new EPA rules forbidding the escape of any fuel or oil vapor to the outside air. The old round-bodied Amal Concentrics (now called Mk I) vented their float chambers to the atmosphere via the tickler valves, which themselves were messy & had to go.

BETTER VENTING
Further, the crankcase & oil tank venting had to be rearranged, as they were ultimately venting out the back via a hose running along the back fender. The T140E addressed this by venting the oil tank to the rocker box, and the engine, breathging through the primary case, was vented to the airbox.

RUNNING GEAR
Sealed wheel bearings replaced the exposed ones that kept failing, and spokes were upgraded to 9-gauge (apparently spokes had begun braking after the introduction of disk brakes with their increased stopping power). New improved fork seals solved the wear problem & could be retrofitted to earlier Oil-in-Frame twins.

A BROWN MOTORCYCLE SEAT?
The Jubilee seat from 1977 had become the standard Triumph motorcycle seat, sans upholstery in wild colors. It could now be finished in all black or even brown, dependent upon paint colors. The top surface's upholstered cross-ribbing now extended partway down the sides of the seat. The nose was narrow for use with slimline gas tanks used in the US.

TRIM
US machines retained their chromed fenders front & rear, but UK machines had painted fenders. The sidecovers were new & completely reshaped. They were painted to match the tank on UK bikes, but were black on US versions.

COLORS
Colors for 1978 were more varied than ever before. US bikes could be ordered with 3 different color combos: Tawny Brown over Gold (pictured here); Astral Blue over Gold; and Black over Crimson. UK models got 2 choices: Tawny Brown over Gold; and Aquamarine over Silver.


1978 Triumph Bonneville SPECIFICATIONS:



MODEL DESIGNATIONS:
1978 Triumph Bonneville T140V..................... 750cc
1978 Triumph Bonneville T140E..................... Emissions

ENGINE:
Engine type....................................... OHV vertical twin
Horsepower at RPM............................ 49 BHP @ 6,200 rpm
Bore................................................ 76mm / 2.79"
Stroke............................................. 82mm / 3.23"
Displacement.................................... 744cc / 40 cu. in.
Compression Ratio............................. 7.9:1
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.......................... 55 degrees BTDC
Exhaust Valve Closes.......................... 27 degrees BTDC

IGNITION:
Ignition Breaker Gap............................. 0.4mm / 0.015"
Spark Plug Gap.................................. 0.50mm / 0.020"
Timing (static).................................14 degrees BTDC
Timing (fully advanced):........................ 38 degrees BTDC

CARBURETORS:
Type................................................ Amal Concentric MKII
Throat Size....................................... 30mm
Main Jet........................................... 210
Needle Jet........................................ .107
Needle Position.................................. 2
Needle Type.......................................D
Throttle Valve.................................... 2
Pilot Jet............................................ 25

TRANSMISSION:
Speeds.............................................. 4
Gear Ratios:
5th - Top........................................... 4.7
4th - Fourth........................................ 5.59
3rd - Third......................................... 6.58
2nd - Second...................................... 8.63
1st - Bottom...................................... 12.25

CLUTCH:
Type................................................ Multi-plate, wet
Number of Plates:
Drive Plates...................................... 6
Driven Plates.................................... 6

SPROCKETS:
Engine............................................. 29 teeth
Clutch............................................. 58 teeth
Gearbox.......................................... 20 teeth
Rear Wheel...................................... 47 teeth

CHAIN:
Primary, pitch.................................. 3/8" triplex
Primary, length................................. 84 links
Final Drive, pitch............................... 5/8" X .400" X 3/8"
Final Drive, length............................. 106 links

CAPACITIES:
Fuel (US versions)............................. 2.5 Imp. gal.
Fuel (UK & export versions)................. 4 Imp. gal.
Oil Tank........................................... 5 pints / 3 L
Gearbox........................................... 1 pt / 500cc
Primary Chaincase............................. 1/4 pt / 150cc
Front Forks....................................... 6.4 oz. / 190cc

TIRES:
Front............................................... 3.25 X 19"
Rear................................................ 4.00 X 18"

SUSPENSION:
Front............................................... Telescopic Forks
Rear................................................ Swing Arm

BRAKES:
Front............................................... 10" / 12.9cm disk
Rear................................................ 7" / 17.78cm SLS

DIMENSIONS:
Seat Height...................................... 32.5" / 77.5cm
Wheelbase........................................ 54.5" / 140.3cm
Length.............................................. 85.5" / 202cm
Width............................................... 28.5" / 72cm
Ground Clearance.............................. 5" / 12.7cm
Weight, unladen................................ 395 lbs / 180kg


SAVE THE BONNEVILLE!
Did you ever wonder what really happened to Triumph? This is the behind-the-scenes story of the Meriden Workers' Co-op, written by John Rosamond, the welder-turned-Company Chairman. From the factory takeover in '73, and the formation of the Co-op in '75, through their endless struggles to continue to produce Triumph Bonnevilles, despite constant setbacks & opposition, until its slow death in 1983. The book is loaded with amazing photos & information you won't find anywhere else. This is not hearsay either, this is the real deal right from the source. I lived through this stuff myself, working as an apprentice mechanic in a Triumph/BSA/Norton dealership in 1971 when the first Oil-in-Frame Triumphs arrived to a lukewarm response. There were lots of ups & unfortunately more downs for the cash-strapped Co-op, but the scrappy Brits soldiered on & even came out with some stunning new models (like the Diana watercooled DOHC 4-valve twin, the contra-rotating balance shaft Bonneville, the 8-valve TSS, Anti-Vibration frames with rubber engine mounts & more), all outlined in the book. It's a MUST READ for anyone who mourns the loss of the British Motorcycle Industry as a whole & of Triumph in particular.


You can order the book by clicking on the picture of the book cover, above.


TRIUMPH MOTORCYCLE BOOKS


TALES OF TRIUMPH & MERIDEN

TRIUMPH MOTORCYCLES: TRIUMPH ENGINEERING CO.

TRIUMPH WORKSHOP MANUAL, 1935-1939

TRIUMPH WORKSHOP MANUAL, 1937-1951

TRIUMPH WORKSHOP MANUAL, 1945-1955

TRIUMPH MOTORCYCLES: FROM SPEED TWIN TO BONNEVILLE

TRIUMPH MOTORCYCLES - HINKLEY RENAISSANCE

SAVE THE TRIUMPH BONNEVILLE

THE INSIDE STORY OF THE MERIDEN WORKERS' CO-OP.
STORY OF THE TRIUMPH BONNEVILLE - MOVIE

TRIUMPH 650 & 750 TWINS

ESSENTIAL BUYERS GUIDE TO TRIUMPH BONNEVILLE

TR BONNEVILLE 2001-08

TR BONNEVILLE, PORTRAIT OF LEGEND

TR BONNEVILLE: T120/T140

TRIUMPH MC RESTORATION

HAYNES TR TRIPLES & FOURS

TRIUMPH 21 TO DAYTONA

TRIUMPH TIGER CUB BIBLE

Triumph Motorcycles
Triumph Bonneville
Triumph Bonneville, Pre-Unit Construction, 1959-1962
Triumph Bonneville, Unit Construction, 1963-1970
Triumph Bonneville, Oil-in-Frame, 1971-1983

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