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tightness of the crank nut. Re-torque it to 40ft-lb if necessary. While you're in there, check the tightness of the clutch centre nut. It should be 70ft-lb.
If a bike has been unused for some time, the crankshaft oil seal on the timing side can harden and fail. If it does, you'll lose oil pressure.
The top end of the T140 can give a little trouble. The main problem is that the rocker arm to valve angle is fairly tight and the action of the rockers across the top of the valve stems puts a bit of stress on the valve guides, which can wear prematurely. Replacement is the only cure. Mushroom headed adjusters (£22 a set) make the valve guide's life easier and quieten the top end down a bit.
The T140's valve seats are perfectly happy with unleaded fuel, so don't be tempted to replace them for the sake of it. They can be re-cut if necessary. The kick-start ratchet pinion nut can work loose, letting the mainshaft move laterally. A dragging clutch is often the first sign of this. Re-tighten to 45ft-lb.
The Mkll Concentric carburettors fitted from 1979 are likely to be worn and can be tricky to set up. Replacement Mikunis are readily available.
Right: 1979 -TI40E is the new base model...
A sump plate filter kit is a worthwhile replacement for the standard gauze strainer and is much more efficient in filtering out the sludge that gathers in the sump.
A stainless steel brake line kit will sharpen up the performance of the T140's discs. Modern brake pads will help too. If you really want to improve braking, twin disc conversions are available for the front end - at a price...
Examine the wiring loom around the headstock area carefully. Over the years, repeated flexing can cause wires to fracture. Fitting a new loom (around £110) isn't a difficult job if you take your time and can eliminate a lot of niggling problems.
The frame is a lot better than the earlier T120 type and handling is good, according to Paul. Outriggers add extra support to the swinging arm and the swinging arm bushes and pins are easy to replace. Replacing the original shocks is a good idea if they are still on the bike.
If you get the chance, check the oil pressure before you buy. You can plumb an oil pressure gauge in where the oil pressure switch fits in the front of the timing cover. Pressure should be 25psi at idle and 65psi at normal running speeds.
Engine type: Bore x stroke: Capacity: Compression ratio: Carburettor: Lubrication: Claimedpower:
Transmission: Ignition: Electrical system:
Wheelbase: Front tyre: Rear tyre: Front brake: Rear brake:
Dry weight: Fuel capacity: Top speed:
air-cooled parallel twin 76 x 82mm 744cc 7.9:1
3ftnm Amal Concentric dry sump 44bhp @ 7000rpm (claimed)
four-speed, multi-plate clutch coil (electronic from 1979)
12 volt Lucas alternator
(three phase from 1979)
4.25 x 18in
7in sis drum
(10in disc from 1976)
...1979-T140D cops the range.
T140ES with electric start joins the Bonneville line-up. Changeover to Veglia instruments now total. Rear brake caliper now mounted above the swinging arm. Colours: Steel Grey and Candy Apple Red or Black, Candy Apple Red and Black or Olympic Flame and Black.
Bonneville Executive (T140EX) - with twin front discs, fairing, luggage, optional cast wheels and Bing CV carburettors -launched. Cylinder head revised to provide stub fitting for exhaust pipes. Colours: Candy Apple Red and Black, Steel Grey and Candy Apple Red, Silver Blue and Black, Smoked Blue or Smoked Flame or Smoked Flame and Ivory.
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