Shift Detent

SHIFT DETENT

A shiftless transmission can sometimes take only five minutes to cure.

by Dain Gingerelli

Ever had your bike’s transmission stick in gear? Or worse yet, tap the shift lever with your toe, only to have the transmission gears shuffle from one to the next? A major engine teardown looms in your head, and with it a giant service bill.

Sometimes the culprit isn’t all that big a deal. It could very well be due to a dirty or broken shift detent plunger. The detent plunger keeps the transmission gears in proper sequence by locking the shift drum into position. If the detent plunger becomes inoperative, the transmission will lock in gear (or neutral), and the rider cannot select the correct gear. If the detent spring is held compressed, then the shift stopper plate (sometimes referred to as the star) will be allowed to freefloat, enabling the transmission to shift itself. Obviously, neither case is desirable.

Correcting this problem is usually very simple. Most motorcycles have access to the shift detent at or near the bottom of the

engine or transmission case. It will generally appear as a drain plug close to the shift mechanism. To service the detent, drain the oil from the transmission, then remove the shift detent for inspection.

Some motorcycles have the detent in odd places. For instance, the Yamaha XS650 has the detent on the right side of the engine, and can be serviced only when the side cover is removed. The SR500, although having the detent in its expected location, is difficult to remove because the side-stand bracket prevents adequate clearance for a flatblade screwdriver to reach the plug (some Yamahas don’t have the familiar hex head bolt, but a slot for flatblade screwdriver). Owners of such as Yamaha RD350s, MX250s, and Kawasaki KZ200s and KL250s will have an easy time locating and removing the detent, as it is near the regular oil drain plug and easy to remove. Most multi-cylinder superbikes have easy access to the detent on the

bottom of the engine case. If you cannot locate the detent screw on your bike’s engine, you might consult the local bike shop, or thumb through the service manual.

Having inspected the detent, determine whether it needs replacing, or just a cleaning out. Often the shift detent spring will accumulate a little dirt or chips of metal from the engine parts. These foreign particles will lodge between the spring’s coils, causing it to stick. To clean, pull the detent apart, then rinse the spring and detent body in cleaning solvent. Make doubly sure there are no dirt or metal shavings in the spring’s coils or in the detent body before reassembly.

After it is cleaned, dry with a clean rag. Put a dab of fresh oil on the spring and in the detent body, then reassemble and put back in the transmission. If this was the only problem with your transmission, a few minutes in the garage has saved you one giant service bill. E3