Zongshen RX3: Starter Motor System

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Starter Motor

The starter motor is attached to the engine behind the cylinder by two bolts.



The driving gear of the starter motor enters the right crankcase half to engage the reduction gears, as shown inside the red oval in the photograph below.



Starter Clutch (Sprag Clutch) Inspection

The starter clutch is located inside the yellow circle in the photograph above. The starter clutch should rotate freely when turned clockwise; it should lock when turned counter-clockwise.

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Starter Motor Reduction Gear Assembly

The reduction gears for the starter motor are designed to prevent damage to the starter motor should the spag clutch fail. As shown below, this assembly consists of two gears. Two washers clamped inside the outer gear are locked to splines on the inner gear. These washers provide enough pressure to turn the starter motor gears, but will spin inside the assembly if the sprag clutch fails.

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Starter Clutch Operation

Since the crankshaft turns much faster than the starter motor, the starter clutch (sprag clutch) is designed to disengage the starter motor from the crankshaft once the engine starts running. The sprag clutch uses steel rollers which lock the crankshaft to the starter gears when turned in one direction, and freewheel when turned in the opposite direction. This allows the starter to lock up solidly when starting the engine, and then release after the engine starts.

The starter clutch has an inner race, and an outer race. The inner race is connected to the starter motor gears. The outer race is connected to the crankshaft. As shown in the diagram below, the starter gears initially lock to the outer race to turn the crankshaft.



As the starter gears turn the outer race, the spring-loaded rollers are forced into the small ends of their tapered slots. This wedges the rollers against both races, locking them together. The starter gears and crankshaft are now locked, and torque is transmitted from the starter motor to the engine.

After the engine starts and is running under its own power, the crankshaft attempts to drive the starter clutch faster than the starter motor. As the crankshaft turns the inner race, this force unloads the clutch rollers, and unlocks them from the outer race of the starter clutch. The unlocked rollers now allow the starter clutch to rotate freely around the crankshaft.

The following video demonstrates how the starter clutch operates.

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RX3 Starter Starter Clutch Assembly

The starter clutch assembly of the Zongshen RX3 is designed with the following components.

Starter Clutch
Starter Clutch Housing
Starter Motor Gear

The starter clutch itself is shown below. The RX3 starter clutch has a different design that the generic sprag clutch shown earlier, but it operates in exactly the same manner. The RX3 starter clutch has an inner race, and and outer race, which are separated by steel rollers. The rollers are held in place with an spring on the inner race which presses the rollers against slanted ramps on the outer race.





The starter clutch is housed inside the starter clutch housing. This housing is placed inside the starter motor gear, and both parts are placed over the counter shaft.

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RX3 Starter Clutch Operation

From 1:50 to 4:50, the following video shows how this type of starter clutch operates.

RX3 Starter Clutch Inspection, and Wear

From 14:23 to 14:47, this video also shows how to inspect the starter gear of the sprag clutch assembly. From 19:50 to 22:10, the video shows how to inspect the sprag clutch.

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Starter Clutch Repair

If the starter clutch assembly does not lock, and rotates counter-clockwise, or the starter clutch begins to malfunction, you should replace the worn parts. After draining the oil and antifreeze, remove the right crankcase cover. Before removing the nut from the crankshaft, you must lock the primary gear of the crankshaft to the driven gear of the clutch basket. You can do this with a penny, or you can use a tool such as the Motion Pro GearJammer.

http://www.motionpro.com/motorcycle/partno/08-0427/

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After removing the nut from the crankshaft, remove the clutch basket, as detailed in the following thread.

http://www.chinariders.net/showthread.php?t=15612

After removing the clutch basket, remove the locking washer, the primary drive gear, and the components of the sprag clutch. These items are shown inside the yellow circle in the photograph below.



Replace the worn parts of the sprag clutch, then install the primary drive gear. Finally, install the safety washer and the nut. Now replace the clutch basket so you can lock the crankshaft. The following thread details how to replace the clutch basket.

http://www.chinariders.net/showthread.php?t=15612

After locking the crankshaft, torque the crankshaft nut to 114 foot-pounds (155 Nm).

Reinstall the right crankcase cover. After replacing the engine oil and antifreeze, the starter clutch repair is completed.