A bit of a run-in
After rebuilding his 250cc Ducati, Tim Oliver asks about running in, having heard conflicting advice whether to take it easy or ride it hard.
Well, I’ve heard that hammering a Honda RC30 from new gave 5bhp more for racing – but I wouldn’t recommend it for older bikes like the Duke.
Running in is mostly about the bore and piston, the large area of which creates a lot of friction heat while they wear together. Triumph advocated 1500 miles, Honda just 600 – but not because Hondas wear out faster, it’s about machining tolerance. When Japanese industry rebuilt after the war, its up-to-date machinery produced unheard-of accuracy. Any two Honda parts were identical – but Triumph (still using machines that actually served in the war) stamped their cylinders H and L – high and low ‘fit’ – to the end.
It’s evolution; in the 1920s, running in included removing the piston to file off ‘high spots’ (shiny patches) and lapping rings with abrasive paste – but on those simple motors it could be done in an hour.
With Tim’s Ducati, I’d start with short runs round the block to make sure nothing’s unhappy, coming loose or getting too hot before taking longer rides. Then, usual advice, don’t slog uphill – it’s better to rev the engine a bit faster than labour it – and for the first few hundred miles avoid undue acceleration – just let the engine build speed. When you start opening up, do it for short stretches at a time and avoid busy roads where other traffic sets the pace.
Bear in mind, too, that the rebore you’ve had done may not match factory standard, so even on Japanese bikes I’d rely on what your engine tells you, not the owners handbook.