Before you buy
All Triumph straight-sixes should start readily hot or cold, though poor hot starting and rough running at tickover were noted PI weaknesses when they were new. Fuel injection was in its infancy at the time, but they can now be made to run much more efficiently. Experience is the key, and there’s plenty of knowledge among the clubs and at specialists, so make use of that and a PI can be a joy to own.
The crank end-float is the only inherent weakness of this engine – catch it early and the thrusts can be replaced in situ, but bad cases can wreck both the block and crankshaft. Otherwise look out for general engine wear and signs of overheating from silted-up radiators and water passages: all parts are available for a rebuild.
The all-synchromesh TR manual gearbox is robust, with optional overdrive on third and top to give much more relaxed motorway cruising. The Borg-warner 35 automatic is also relatively understressed, lasts well and neither transmission is expensive to rebuild.
Check the differential for oil leaks and the driveshaft splines for clonks. Driven hard, especially in the higher-powered models, they can stick under torque and cause disconcerting wiggles from the back end between power on and off. There are solutions to this using Datsun driveshafts if it bothers you, but in normal driving you’ll never notice it.
The brakes are perfectly adequate if well maintained, with decent-sized discs up front and 1.75in-wide shoes in the rear drums.