A Ryobi 4-cycle gas trimmer uses a piston that requires four strokes to power, vent exhaust, intake fuel, and give compression. Instead of the oil coming from the fuel source, as in two-cycles, a four-cycle needs lubrication directly to the crankcase. This requires a constant monitoring of oil levels, adding oil, and changing the oil when necessary.
Type of Oil
The lubrication of the engine is critical to keep the piston from seizing. If the oil level isn't maintained, the piston will seize quickly, sometimes in a matter of minutes. The type of oil used in Ryobi four-cycles must be a SAE 10W30. This oil will work at all temperatures. However, the oil must have an American Petroleum Institute service classification of SJ, which will be located on the bottle. All other oils, including two-stroke engine oil, can never be used in the engine.
Checking the Oil
Check the oil level before every use to ensure the proper lubrication. Place the engine, fuel tank down, on top of a bench or flat work space. Let the cutting shaft and head extend off the bench, so the cutting shield is facing down. Tilt the engine on to its side, with the oil fill hole up, to check the oil level. Wipe the area clean with a rag so nothing falls in before opening the plug. Open the plug and check the dipstick. The oil should fall within the hatched area on the dipstick. If oil doesn't reach this level, add more oil.
Refilling the Oil
Add oil whenever the engine gets low. Don't wait until the next scheduled oil change. If oil is found to be low, clean the area around the fill hole with a rag. Pour in the recommended SAE 10W30 oil slowly. Allow the oil to settle into the crankcase and check the oil level. Fill the oil until it reads in between the hatched area on the dipstick. Refit the oil cap tightly to the engine when finished. Wipe off any spilled oil before using the trimmer again. If using a large bottle of oil, use a small funnel to guide the oil into the crankcase.
Changing the Oil
Change the oil after every 25 to 30 hours of operating time. Change the oil only after the engine is warm. This allows you to dump it out more easily and also removes more impurities that can build up during the last period of use. Don't change the oil when the engine oil is still hot. Wait at least 10 minutes for the engine to cool before changing the oil. Remove the oil fill cap and tip the engine on its side so the oil will flow into a pan or oil container. After the oil has drained, fill the oil tank with the recommended oil.