Not only is loctite not an answer to poor design / inspection but it has to be realised that tightening the nut is not what keeps keyed pulleys / hubs on to shafts. The shaft and pulley have to be a light interference fit and there must be no clearance on the flanks of the key in either of them. If the key can be top and Botton fitted as well, so much the better. The only reason for the nut being there is to stop the pulley sliding off the end of the shaft. If a keyway is loose and can move even slightly it will undo the nut in the first few seconds of running.
Long gone are the days when all keys were hand fitted and therefore inspected by the fitter. These days the work is deskilled and keys and keyways are made to assemble as produced and the danger is that when manufacturing tolerances fall outside the design tolerances the the only thing to save the day is the inspection dept. picking up the error. Inspection relies more and more on statistics to provide adequate sampling and a small number of failures is regarded as a fair price to pay for the money saved. There are, in fact, statistics to provide acceptable failure rates - higher rates in lower cost vehicles and ( as I was taught at college) zero at Rolls Royce!
Sorry to hear of your expensive breakdown Graham but you are, after all, just one more statistic.
