there's a bad burning smell coming from my saw near the motor, and sometimes a little smoke

Diagnosis

The burning smell and smoke emanating from the motor housing of your Ryobi ONE+ 18V Reciprocating Saw (P519) indicate that the armature windings or the carbon brushes are overheating. This is typically caused by "stalling" the motor under heavy load, which creates an electrical surge that exceeds the thermal capacity of the enamel insulation coating the copper wires. When this insulation melts, it releases a pungent, acrid smoke and a distinct burning plastic scent. This happens most frequently when the user applies excessive forward pressure, forcing the motor to fight against the material rather than letting the blade's teeth clear the kerf. You can confirm this by checking the motor vents; if you see a grayish-white residue or smell ozone near the rear of the tool, the motor is struggling. If the tool continues to run but smells, you have likely suffered partial insulation failure; if the tool has lost power or "stutters," the motor may be shorting internally.

How to Fix It

If the tool is still operational, you must immediately cease all cutting and perform a deep thermal reset and mechanical audit to prevent a total motor burnout.

1. Immediate Power Down: Remove the 18V battery pack immediately. Do not simply pull the trigger off; physically disconnect the power source to stop the current flow to the overheating windings.
2. Thermal Cool-Down: Allow the tool to sit for at least 30 to 60 minutes. Using compressed air, blow out the motor vents at the rear of the saw to remove sawdust and debris that may be trapping heat inside the housing.
3. Blade Inspection: Remove the current blade. Check for "rounding" of the teeth or discoloration from heat. If the blade is dull or the wrong TPI (teeth per inch) for the material, discard it. Replace it with a high-quality carbide-tipped blade for dense materials or a fine-tooth metal blade for steel.
4. Load Testing: Reinsert the battery and run the saw in open air (no material) for 10 seconds. If the smell persists without a load, the motor is permanently damaged. If the smell is gone, proceed to test on a soft piece of scrap wood.
5. Pressure Adjustment: When cutting, apply only enough pressure to keep the blade engaged. If the motor RPMs drop significantly, back off the pressure immediately to allow the motor to regain speed and cool via the internal fan.

If That Didn't Work

• Replace the Carbon Brushes: If the smoke was localized to the brush holders, the brushes may have worn down to the springs, causing electrical arching. While the P519 is a sealed unit, experienced users can open the housing to inspect the brushes for pitting or excessive wear. If they are charred, they must be replaced.
• Check the Trigger Switch: A failing trigger switch can cause "voltage leakage" or a partial connection, which creates localized heat and a burning smell. If the trigger feels "mushy" or doesn't click firmly, the switch assembly may be melting internally and requires replacement.
• Inspect the Gearbox Lubrication: Sometimes the "burning" smell isn't electrical but mechanical. If the grease in the reciprocating gear housing has leaked or dried out, the metal-on-metal friction generates extreme heat. Open the gear case and apply a high-temp lithium grease to the drive mechanism.
• Battery Health Check: Use a multimeter to ensure your 18V battery isn't sagging. A battery with high internal resistance can cause the motor to draw current inefficiently, leading to overheating. Try a fresh, fully charged High-Performance battery to see if the symptom persists.

Heads Up

• Avoid "Forcing" the Cut: If you have to lean your body weight into the P519 to make it cut, you are overloading the motor. Let the stroke speed do the work.
• Match Blade to Material: Using a coarse wood blade on metal or a fine metal blade on thick timber creates massive friction and heat, leading directly to motor failure.
• Keep Vents Clear: Never block the rear cooling vents with your hand or clothing during operation, as this kills the airflow needed to dissipate heat from the armature.
• Duty Cycle Awareness: The P519 is a cordless tool with a specific duty cycle. For heavy-duty demolition, allow the tool to idle for 30 seconds every few minutes to let the windings cool.