A slipping clutch can be an aggravating problem, and is usually a sign of extensive wear in your Yamaha YFZ450's transmission. Slips and drags typically appear as a lag in power when the throttle is applied, or as a slight forward creep while the clutch is disengaged. While a incorrectly adjusted clutch cable can cause similar issues, clutch slips are indicative of worn clutch springs and clutch plates. Determining the exact problem requires that you disassemble and inspect the clutch.
- 8, 10 and 17 mm sockets
- Socket wrench
- Resealable oil drain container
- Torque wrench
- Vernier caliper
- Clutch springs
- 2 quarts, SAE 10W-40 Type SF engine oil
- Clutch plates
Remove the oil drain bolt from the bottom of the engine crankcase, using a 17 mm socket and a socket wrench. Drain the engine oil into a resealable oil drain container, then screw the drain bolt into place. Tighten the bolt to 22 foot-pounds, using a torque wrench.
Loosen the clutch cable adjusting nut, located behind the clutch lever perch on the left handlebar, then turn the cable adjuster clockwise by hand until it is seated against the clutch lever perch to completely loosen the cable. Pull the clutch cable end ferrule out of the clutch release arm, located on the right side of the engine.
Remove the clutch cover and gasket from the right side of the engine, using an 8 mm socket.
Unscrew all six spring bolts from the center of the clutch pressure plate, using a 10 mm socket. Pull the clutch springs out of the clutch pressure plate spring wells. Measure the clutch springs, using a vernier caliper. Replace all six springs as a set, if any of the springs have a measurement less than 1.97 inches (50 mm). Set the springs aside, if all six springs are longer than 1.97 inches.
Pull the clutch pressure plate out of the clutch basket. Pull all 15 clutch plates out of the clutch basket. Set the last fibrous friction plate, the plate closest to the engine, aside.
Measure the thickness of all seven fibrous friction plates. Ideally, the plates must be between 0.114 to 0.122-inches (2.9 to 3.1 mm) thick. If any of the friction plates are thinner than 0.114-inch, all 15 clutch plates must be replaced.
Lay the steel clutch plates individually on a smooth, level work area. Slip a 0.0079-inch (0.2 mm) feeler gauge under the clutch plates to check for warping. Replace all 15 clutch plates if the feeler gauge can move freely under any portion of the steel plates, indicating that the plate is warped beyond its service limit.
Soak all 15 new clutch plates int SAE 10W-40 Type SE or SF engine oil for a minimum of 12 hours. Skip this step if you are not replacing the clutch plates.
Slide the larger friction plate into the clutch basket, followed by a steel plate. Alternate between the remaining fiber and steel plates until you have installed all 15 plates into the clutch basket.
Push the clutch pressure plate over the clutch plates, then insert the clutch springs into the spring wells. Screw the spring bolts into place and tighten them to 5.8 foot-pounds.
Reinstall the clutch cover and gasket onto the engine. Tighten the cover bolts to 7.6 foot-pounds. Slip the clutch cable end ferrule into the clutch release arm, then turn the clutch cable adjuster on the left handlebar counterclockwise to tighten the cable.
Pull the clutch lever in until you feel resistance, then measure the distance between the edge of the lever and the lever perch. Ideally, there must be a 1/8-inch gap between both parts. Loosen or tighten the clutch cable until the gap is exactly 1/8-inch, then tighten the clutch adjuster nut against the clutch lever perch by hand.
Unscrew the oil tank filler cap by hand. Fill the oil tank with 1.64 quarts of SAE 10-40 Type SF engine oil, then screw the filler cap into place.
- Yamaha YFZ450S Service Manual; Yamaha Motor Corp.