The tach head is constructed similarly to the speedometer unit, with the exception of the mileage numbers. Most tachs in the CX & GL series also incorporate a temperature gauge in the unit. But the opening, lubing and servicing the unit is similar.
Both units register their information by a needle that is connected to a half hemisphere that rotates within another half hemisphere at a angle. The shells are magnetized and as one turns, it drags the other along thru magnetic action. This is a ingenious method of providing a indicating needle approximately 350 degrees of movement, while using a rotating input from the engine. The needle uses a hair spring to return the needle to its stop.
Lubrication is the same as the speedometer unit, with no points of lube for the mileage register. A bouncing tach needle is usually due to lack of lube in the entrance bearing or the inner cable. To address the entrance bearing lube, the tach should be removed from the bike and placed with the cable entrance at a vertical up position. Add 4-5 drops of light machine oil to the outer area of the inner shaft and turn the shaft with a screwdriver to allow the lube to flow downward into the bearing. Leave the head set for a few minutes and re-install.
by Blue Fox
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