1978 Triumph Bonneville

ABOVE & BELOW: 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.
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


T140V Bonneville

T140E Bonneville

Engine type

Displacement

Bore & Stroke

Compression

Carburetors

Ignition

Engine output

Primary drive

Primary sprockets

Clutch

Gearbox

Ratios, overall:

1st, bottom

2nd

3rd

4th

5th, top

Final drive

Final drive sprockets

Frame type

Suspension, front

Suspension, rear

Brake, front

Brake, rear

Tire, front

Tire, rear

Fuel capacity

Wheelbase

Seat height

Ground clearance

Weight

5-speed 750 Roadster

5-speed 750 "Emissions"

Air-cooled OHV vertical twin

744cc / 45.0 ci

76mm X 82mm / 2.99" X 3.23"

7.9:1

2- Amal Concentrics MkII, 30mm

Battery & coil, Lucas

49 bhp @ 6200 rpm

3/8" triplex X 84 links

Engine 29T X Clutch 58T

Multi-plate, wet

5-speed constant-mesh, left-foot shift


12.25:1

8.63:1

6.58:1

5.59:1

4.7:1

5/5" X .400" X 3/8" chain X 106 links

Gearbox 19T X Rear 47T

All-welded, oil-bearing large-tube backbone

Telescopic fork, hydraulic damping 2-way

Swing arm, 2 Girling dampers

10" disk, 2-piston hydraulic caliper

10" disk, 2-piston hydraulic caliper

3.25" X 19" Dunlop, ribbed

4.00" X 18" Dunlop, universal

3 Imp gal (US) / 4 Imp gal (UK & export)

54.5" / 140.3 cm

32.5" / 77.5 cm

5" / 12.7 cm

395 lbs/ 180 kg


MORE TRIUMPH BONNEVILLES:
Triumph Bonneville
Triumph Bonneville Pre-Unit (1959-1962)
.....1959
.....1960
.....1961
.....1962
Triumph Bonneville, Unit-Construction(1963-1970)
.....1963
.....1964
.....1965
.....1966
.....1967
.....1968
.....1969
.....1970
Triumph Bonneville, Oil-in-Frame
.....1971
.....1972
.....1973
.....1974
.....1975
.....1976
.....1977
.....1978
.....1979
.....1980
.....1981
.....1982
.....1983
Les Harris Bonnevilles(1983-1989)
OTHER TRIUMPHS:
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Triumph TR7
Triumph Trophy
Triumph Tiger
Triumph Thunderbird
Triumph Trident
Triumph X-75 Hurricane


Check out these TRIUMPH BOOKS


TALES OF TRIUMPH MOTORCYCLES & THE MERIDEN FACTORY


COMPLETE BOOK OF CLASSIC & MODERN TRIUMPHS


TRIUMPH BONNEVILLE & TR6


TRIUMPH MOTORCYCLES, THEIR RENAISSANCE & THE HINKLEY FACTORY


TRIUMPH SPEED TWIN & THUNDERBIRD BIBLE


HINKLEY TRIUMPH TRIPLES & FOURS ESSENTIAL BUYERS GUIDE


TRIUMPH PRODUCTION TESTERS’ TALES FROM THE MERIDEN FACTORY


TURNER’S TRIUMPHS: EDWARD TURNER & HIS TRIUMPH MOTORCYCLES


TRIUMPH TROPHY BIBLE


HINKLEY TRIUMPHS, THE FIRST GENERATION


BONNIE: THE DEVELOPMENT OF THE TRIUMPH BONNEVILLE


TRIUMPH: A CENTURY OF PASSION & POWER


TRIUMPH TWIN RESTORATION


CONENTRY’S BICYCLE HERITAGE


HOW TO RESTORE YOUR BSA ROCKET III/TRIUMPH TRIDENT


TRIUMPH & BSA TRIPLES: THE COMPLETE STORY OF THE TRIDENT & ROCKET 3


TIGER CUB BIBLE


TRIUMPH SINGLES: EARLY DAYS TO 1974 BY ROY BACON


BRITISH MOTORCYCLES: TRIUMPH


TRIUMPH MOTORCYCLE RESTORATION, PRE-UNIT


TRIUMPH PRE-UNIT TR5, 5T, 6T, T100 & T110 FACTORY SHOP MANUAL


TRIUMPH MOTORCYCLE RESTORATION


ILLUSTRATED TRIUMPH MOTORCYCLE BUYER’S GUIDE BY ROY BACON


FACTORY ORIGINAL TRIUMPH TWINS 1938-1962


TRIUMPH BONNEVILLE: PORTRAIT OF A LEGEND


TRIUMPH 650 & 750 TWIN REPAIR MANUAL 1963-1983, BY HAYNES


TRIUMPH MOTORCYCLES IN AMERICA


TRIUMPH BONNEVILLE 2001-2012 REPAIR MANUAL BY HAYNES


TRIUMPH BONNEVILLE: THE ESSENTIAL BUYERS GUIDE


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TRUIMPH MOTORCYCLES: FROM SPEED TWIN TO BONNEVILLE


BOOK OF TRIUMPH TWINS BY CLYMER


TRIUMPH BONNEVILLE BIBLE, ALL MODELS 1959-1983


TRIUMPH TIGER CUB & TERRIER 1952-1968 REPAIR MANUAL BY HAYNES


TRIUMPH RACING MOTORCYCLES IN AMERICA


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TRIUMPH 675 DAYTONA & STREET TRIPLE REPAIR MANUAL, 2006-2010


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TRIUMPH 350 & 500 UNIT TWINS ESSENTIAL BUYERS GUIDE


TRIUMPH TWIN RESTORATION BY ROY BACON


TRIUMPH BONNEVILLE & TR6 MOTORCYCLE RESTORATION GUIDE


TRIUMPH: RETURN OF THE LEGEND


BSA & TRIUMPH TRIPLES: GOLD PORTFOLIO


TRIUMPH MOTORCYCLE RESTORATION GUIDE: BONNEVILLE & TR6


TRIUMPH THUNDERBIRD 6T ROAD TEST 1966


TRIUMPH 500-750 TWINS 1963-1979, SERVICE, REPAIR & PERFORMANCE MANUAL


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TRIUMPH ILLUSTRATED WORKSHOP MANUAL 1937-1951 BY ROY BACON


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TRIUMPH OWNERS MANUAL: UNIT CONSTRUCTION 350 & 500 TWINS

TRIUMPH INSTRUCTION MANUAL: TRW 499cc SV TWIN


TRIUMPH SPEED TWIN INSTRUCTION BOOK FOR 1939


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2010-14 TRIUMPH TIGER 800 HAYNES SERVICE MANUAL


TRIUMPH 650 & 750 TWINS: BONNEVILLE, TIGER, TROPHY & THUNDERBIRD


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TRIUMPH MOTORCYCLE RESTORATION, BY TIM REMUS


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TRIUMPH FUEL INJECTED TRIPLES 1997-2000


TRIUMPH SINGLES: EARLY DAYS TO 1974, BY ROY BACON


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CHILTON’S REPAIR & TUNE-UP GUIDE, TRIUMPH THROUGH 1972


OVERHAUL MANUAL FOR TRIUMPH 3-CYLINDER ENGINE


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TRIUMPH WORKSHOP MANUAL FOR 750 BONNEVILLE & TIGER


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TRIUMPH 650 & 750 UNIT TWINS 1963-1983, HAYNES REPAIR MANUAL


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TRIUMPH PRE-UNIT TWINS WORKSHOP MANUAL


TRIUMPH 350/500 TWINS WORKSHOP MANUAL






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