Small but effective

Tapers have been used on engines for more than a century. They offer a reliable way of connecting large rotating masses such as the Yamaha’s rotor or the crank pin of a pushed-up crank shaft. Splined joints might seem like a better idea but they require a dramatic step-up in manufacturing technology and are infinitely less tolerant of machining variances. Tapers are also significantly cheaper to knock out repeatedly. The fit between parts is key to their joint (sic) effectiveness; too sloppy and the coupling will fail in use, too tight and the parts won’t go together. All tapered parts are machined to a tolerance and if that’s on the lax side of ideal the joint will be easier to separate. Get both parts bang on and it can be almost impossible to break their bond. A good mate used to race CS series Yamahas in the Classic Series and has taken literally dozens apart but still had some 20% that would only come off using an angle grinder.