Quote:
Originally Posted by leathermang
Actually I think that where precise timing is needed a key is more often used..
A tapered (friction ) fit is often used to protect something in the power line...as with using the friction of a Morse Taper in a lathe... where you WANT it to give way under certain drastic situations and limit the damage by letting the power go on down the line..
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For timing a VW diesel engine, the cam nut is left loose while engine is rotated to TDC before the cam nut is tightened. In the VW, the taper on the cam is for precise timing, not for protection of the cam, which bends valves and breaks the cam if the engine goes out of time for whatever reason. The taper IMO is for precise alignment of the pulley for less pulley run out and wobble, same reason the morse taper is used in morse taper drill bits.