Shims: the savage scourge of the humble home mechanic

Back in the late 1960s and very early 1970s Ducati was a strange little Italian firm with a reputation for random quality control, hit and miss electrics, variable paint and plating finishes, along with a parsimonious approach to spares support. The late author, Mick Walker, was one of the few dealers who truly understood the Ducatis of the period. A Ducati built and/or sold by Mick was normally one of the best there was. At the time the only models on offer were four-stroke singles and they were nothing like the contemporary BSAS. Get a good Ducati and it was a thing of sheer bliss but buy a wrong ‘un and it could be pure, undiluted, malevolent hell. As someone cynically suggested, the Ducati factory of the period might very well have been a shim manufacturer that made motorcycles as a means of getting rid of surplus stock: scurrilous possibly, but not without an element of truth. Ducati, like many other Italian engineering firms, was beset by industrial unrest, political turmoil, unions with Communist leanings, remote distant management and poor infrastructure. The drawings that came off the designer’s desks were generally superbly accurate but the shop floor often lacked the resource and/or will to machine with the necessary levels of accuracy. This led to the age-old practice of shimming, which was needed to ensure correct tolerances and clearances. Based upon necessity the use of shims became the norm as the chase for performance overtook the limits of period production techniques. It was a quick and easy fix for cash strapped factories receiving minimal investment but a migraine in metal for aspirant home mechanics. European, American and British factories had come to rely on the humble shim as a get-out-of-jail-free card but it was the Japanese who ousted most of them. By investing in precision casting and carefully controlled, accurately, repeatable, machining shims were rapidly, and thankfully, made almost obsolete.