1981 Triumph Bonneville


ABOVE: The 1981 T140ES Executive was a factory touring bike, with sport fairing & saddle bags (panniers).

MORE SPECIAL MODELS
The 1981 Triumph Bonneville attempted to address dwindling sales with what had become “Limited Edition”-madness. Not that it was a bad thing, they turned out some pretty nice bikes. But, the problems Triumph was facing couldn’t be solved by cobbling together yet another tarted up version of the same old tired 1937 design. But, that didn’t stop them. More power to ’em!

MODEL DESIGNATIONS
Meriden came out with no fewer than 3 new versions of the 1981 Triumph Bonneville. The first two were variants of the 1981 Triumph Bonneville Executive, meant to be the touring version, in both kickstart & electric start versions. These came with fairings, top box (touring pack) & panniers (hard saddle bags). The third bike was intended for Police duty & was being evaluated for that purpose. This final 1981 Triumph Bonneville variant was called the T140AV, the “AV” ambitiously designating “Anit-Vibration”, which used rubberized engine mounts to quell the vibes. At that time, BMWs boxer-twins were getting the lions share of Police business in Europe & the UK, partly because they were very smooth, but also very reliable. Neither of which could be said for the Triumph Bonneville, unfortunately.

ENGINE MODS
The 1981 Triumph Bonneville model year began with Engine #KD28001. Engine mods were few. The TDC locating hole was itself relocated to its former position in front of the engine, because the starter was now in the way & the crankshaft was notched accordingly. There was a new heavy duty 4-lipped roller main bearing on the timing side. The oil feed to the exhaust tappets was blocked off. The old-style screw-in exhaust spigots & finned clamps made their return. Oil seals were added to the exhaust valve guides.

NEW CARBS
Every tightening emissions standards forced a move from the Amal Concentric MkII carburetors to the 32mm German-made Bing Type 32 CV (Constant Velocity) carbs for the US market. Early T140Es & T140ESs & all home-market 1981 Triumph Bonneville Executive models were delivered with the Amal MkIIs. The clutch was massaged with thinner plates with cork faces, down to 6 plates from 7 & lighter springs were installed. Starting mid-year, the higher-output alternator of the ES version was now installed on all units, with or without electric start, presumably to simplify production.

SEEKING NEW SUPPLIERS
As a sign of the times, Triumph Motorcycles ceased to be the high-volume component purchaser it had once been, so many of its suppliers moved on. Girling rear shocks & Lucas chromed turn signals ran out mid-year & had to be sourced elsewhere. Time was running out for the Triumph Bonneville. Pity, that.

BELOW: A complete set of factory panniers (saddle bags).


1981 Triumph Bonneville SPECIFICATIONS

T140E Bonneville

T140ES Bonneville

T140D 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

Standard Roadster

Electric Start Roadster

Bonneville Special

Air-cooled OHV vertical twin

744cc / 45.0 ci

76mm X 82mm / 2.99″ X 3.23″

8.6:1

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

403 lbs/ 183 kg

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