chainsaw starts but chain won't move when i pull the trigger. oiler works fine. is the motor burnt out?

Diagnosis

The fact that you hear the motor spinning up when you pull the trigger, combined with a functioning oiler, confirms that the brushless motor and the battery interface are operational. The root cause is a mechanical disconnection between the motor's output shaft and the drive sprocket. In the Ryobi 40V HP RY405110, this is typically caused by a failure of the centrifugal clutch assembly or a sheared drive key. Because this is a brushless system, the motor generates high torque instantly. If the chain binds or hits a hard knot in the wood, the clutch is designed to slip to protect the motor from burning out. Over time, the internal clutch springs can lose tension or snap entirely, or the friction plates can wear down to the point where they no longer grip the outer drum. You can confirm this by running the tool for a second; if you hear the high-pitched "whine" of the motor increasing in RPMs but the chain remains stationary, the motor is healthy, but the power isn't reaching the bar.

How to Fix It

To resolve this, you need to inspect and likely replace the clutch assembly (Part #RY405110006). Follow these precise steps:

1. Remove the battery and ensure the tool is completely powered down.
2. Loosen the bar and chain tensioning nut and remove the guide bar and chain entirely to clear your workspace.
3. Locate the drive sprocket. Note that the sprocket nut is a **left-hand thread** (reverse thread); you must turn it clockwise to loosen it. Use a deep-well socket to avoid stripping the nut.
4. Slide the sprocket drum off the shaft. Inspect the inner splines of the drum and the output shaft of the motor. If the splines are rounded off or "stripped," the assembly must be replaced.
5. Attempt to rotate the motor shaft by hand. If the shaft spins but the drum does not move with it, the internal clutch springs have failed.
6. Install the replacement clutch assembly. Align the drive key precisely in the slot to ensure the sprocket seats fully against the motor housing.
7. Tighten the left-hand thread nut firmly, but do not over-torque, as this can warp the clutch housing and cause the chain to bind during operation.
8. Reinstall the bar and chain, adjusting the tension until the chain snaps back to the bar rail when lifted 1/4 inch.

If That Didn't Work

• Check the Chain Brake Trigger: Ensure the front hand guard (the chain brake) hasn't been accidentally tripped. If the brake band is locked around the clutch drum, the motor will spin the internal components, but the drum will be held stationary. Pull the guard handle back firmly until it clicks to reset the brake.
• Inspect the Drive Gearbox: If the clutch is intact but the sprocket isn't turning, the internal planetary gears in the reduction gearbox may have stripped. This is rare but happens during severe "pinch" events. This requires a full gearbox replacement, as the unit is sealed and not serviceable.
• Verify Battery Voltage: While the motor sounds like it's running, a degraded battery cell can sometimes provide enough voltage to spin the motor at low load but fail to provide the "burst" current needed to engage the clutch. Try a fully charged, high-capacity 40V HP battery to rule out voltage sag.

Heads Up

• Always use a high-tack bar and chain oil; running the chain dry increases friction and heat, which can warp the clutch drum and lead to premature failure.
• Never "force" the saw through a cut that is too wide for the bar length, as this puts extreme lateral stress on the clutch assembly.
• Check the sprocket area for sawdust buildup every 3-4 batteries; packed debris can jam the clutch mechanism and prevent it from engaging fully.
• Ensure you are using a genuine Ryobi 40V HP battery; off-brand batteries often lack the precise current delivery required for the brushless controller to engage the high-torque clutch.