1970 Triumph TR6 Problems: 6 Known Issues

On the 1969-1976 Triumph TR6, the straight-six uses semicircular (half-moon) crankshaft thrust washers at the centre main rather than full-circle thrusts, and the soft lead-indium face wears quickly. As they wear, crankshaft end float grows beyond the 0.006–0.008 in spec; past about 0.015 in the coating is gone and once the alloy wears through to steel it accelerates, scoring the crank thrust faces and eventually letting a washer drop into the sump. Riding the clutch at stoplights drives the wear hard. Worst case the crank walks fore-and-aft and destroys the block thrust faces — a full bottom-end job.

On the 1969-1976 Triumph TR6, the diff is hung from the frame on a forward 'mustache' bracket and rear mounts. The forward differential mounting points are prone to cracking; the right-front point fails first because it carries the most torque load. As the mount works loose the crack propagates and, if ignored, the mounting studs eventually tear out of the frame, letting the diff move under power. The classic tell is a rear-end 'clunk' on sudden throttle application that starts intermittent and progresses to every power-on/off transition.

On the 1969-1976 Triumph TR6, like most British cars of the era the TR6 runs Lucas electrics with bullet-connector harnesses, a 16/17ACR alternator and lots of in-line earths through the body and bulb holders. Decades of corrosion at terminal blocks, the positive battery cable connections, the brown feed wires and the ignition-warning-light circuit (alternator brown/yellow + ignition white) cause flickering lights, no-charge faults, and a warning lamp that lies. Owners report that even a brand-new harness won't fix a charging fault when the real problem is a corroded earth or a tired regulator/alternator.

On the 1969-1975 Triumph TR6, european-market TR6 PI cars use the Lucas mechanical petrol-injection system, fed by a Lucas high-pressure pump. It is notoriously difficult to set up and live with: hard hot-starting after standing, blocked injectors, throttle-shaft wear that wrecks the mixture balance, and a pump/metering unit that ages poorly. Early TR5/TR6 PI tanks also lack an anti-surge reservoir, so on a tight left-hander below a quarter tank the engine fuel-starves and stumbles. This is the single most temperamental system on the car for a restorer.

On the 1969-1976 Triumph TR6, the TR6's small 16 x 16.5 in radiator and engine-driven fan leave little cooling margin, so cars run hot idling in traffic and in hot climates, especially once the original brass core is partially silted up or the timing/mixture isn't right. The factory fan moves little air at idle, and a clogged or tired radiator pushes temperatures into the danger zone in stop-and-go driving.

On the 1969-1976 Triumph TR6, the TR6's semi-trailing-arm independent rear suspension relies on soft rubber bushings at the trailing-arm pivots and fixed (non-adjustable) factory brackets. After decades the rubber perishes and collapses, letting rear camber and toe wander under load, which gives the car a vague, darty rear end, uneven inner-edge tyre wear, and clunks. The fixed factory bracket also can't correct the excessive negative camber a sagged car develops, and stresses the inner mount (a contributor to the trailing-arm bracket cracking restorers see).