T120 Triumph Bonneville Pros
Looks: Most view the '59 T120 as the ultimate Triumph.
Reliable: Good, but expect niggling electrical issues.
Sound: Wonderful exhaust burble (but clattery top-end).
Spares: Most parts available without much trouble.
Re-sale: Bonnies sell easy. '59/'60 and '68/'69 in demand.
Investment: Excellent. Pre-units are still moving ahead.
Economy: 55-60mpg touring across the Bonneville range.
Maintenance: Straightforward. All problems understood.
Tuneable: Very. 750cc kits and hotter cams available.
Starting: Easy. Just tickle, prime, press, go and smile.
Gearbox: Early 4-speeds good. Later 5-speeds better.
Clutch: A little heavy, but reliable and competent.
Pre-unit construction: Traditionalists love this set-up.
Unit construction T120s: 1963-1970. The best all round?
Build: Special old-world quality to pre-unit Bonnevilles.
Coolness: Need a crowd? Ride an early pre-unit example.
T120 Triumph Bonneville Cons
Handling: High speed wobbles. Feeble early frames.
Brakes: SLS drums inadequate. TLS Good. Marginal conicals.
Electrics: Bonnies are prone to vibration damage.
Lighting: Inadequate for high speed back roads.
Vibration: Crank balancing essential. Loose nuts are common.
Oil-in-frame: 1971-1973 models are less desirable.
Early-oil-in-frame: Seat is too high for many riders.
Suspension: Crude fork. Marginal rear springs/swinging arm.
Security: Pre-unit Bonnies are prime targets for thieves.
Top end: Often high wear rate (20k miles), but easy rebuild.
Riding position: Never ideal. Consider rear-sets, or similar.
Mechanical noise: Triumphs are famous for it. No big deal.
Prices: Pre-units are priced for collectors, not daily riders.
Carburettors: Twin set-up needs regular balancing/optimising.
Crank: Tip: strip old engines. Flush the sludge trap. Vital.
Zener diode: Pre-1966 T120s are 6-volt. Upgrade to 12-volt.
Oil leaks: Can be made oil tight, but few are. Still great bikes.