Purchase air motor oil and grease specifically designed for your air tool. Check your specific manufacturer's specifications.
Disconnect the right-angle grinder from the air supply.
Insert a small amount of oil into the air inlet of the grinder. Add approximately one-half teaspoon of oil.
Reconnect the air supply and run the tool for a short time to allow the oil to circulate.
Add more oil after every 2-3 hours of tool operation.
Disassemble the tool head after every 8 hours of operation. Add grease to all of the internal gears and bearings according to manufacturer's specifications.