Small engines, commonly found in equipment like lawnmowers, generators, and garden tillers, require effective lubrication to reduce friction, dissipate heat, and ensure smooth operation and longevity. While methods can vary depending on the engine type and design, a very common approach, particularly in horizontal crankshaft engines, is splash lubrication. Other methods include pressure lubrication and mixing oil directly with fuel in two-stroke engines.
Common Small Engine Lubrication Methods
Understanding how your specific small engine is lubricated is crucial for proper maintenance. Here are the primary methods:
1. Splash Lubrication
This is one of the simplest and most widespread lubrication systems used in many small, single-cylinder engines, especially those with horizontal crankshafts. The system relies on the movement of engine parts to distribute oil stored in the crankcase.
How Splash Lubrication Works:
Based on the mechanics seen in many horizontal crankshaft engines, including those like Briggs & Stratton designs:
- A dipper is attached to the connecting rod (or sometimes the crankshaft).
- As the crankshaft rotates, the dipper dips into the oil reservoir located in the bottom of the crankcase.
- The dipper picks up oil from the reservoir.
- With each rotation, the dipper spreads this oil across bearing surfaces and other critical moving parts, such as the crankshaft main bearings, the connecting rod bearing, the piston skirt, and the cylinder walls.
- This splashing action occurs continuously as the piston travels through the cylinder, ensuring a constant supply of lubricant to prevent metal-on-metal contact.
This method is effective for engines operating at relatively low speeds and loads, where the splashing action is sufficient to get oil where it's needed.
2. Pressure Lubrication
More sophisticated small engines, often found in riding lawnmowers, generators, or small tractors, may use a pressure lubrication system. This system is similar to those found in car engines.
How Pressure Lubrication Works:
- An oil pump (gear or rotor type) is driven by the engine.
- The pump circulates oil from the reservoir through passages drilled into the crankshaft, connecting rod, and engine block.
- Oil is forced under pressure to critical bearings (crankshaft, connecting rod) and sometimes overhead valve components.
- Other parts, like cylinder walls and piston skirts, may still rely on splash from the pressurized oil exiting the bearings or a combination of pressure and splash.
This method provides more controlled and consistent lubrication, especially for high-load or higher-RPM components.
3. Two-Stroke Mix Lubrication
Two-stroke engines, commonly used in chainsaws, leaf blowers, and some older motorcycles, do not have a separate oil reservoir in the crankcase.
How Two-Stroke Mix Lubrication Works:
- A specific type of oil is mixed directly with the fuel before it is put into the fuel tank.
- As the fuel-oil mixture enters the crankcase (which acts as part of the intake path), the oil separates from the fuel.
- The oil then lubricates the crankshaft, connecting rod, piston, and cylinder walls as the fuel-air mixture travels towards the combustion chamber.
- The oil is burned during combustion along with the fuel, which is why two-stroke engines often produce more smoke and have different emissions profiles than four-stroke engines.
Comparison of Methods
| Method | Engine Type | Oil Location | Distribution Method | Separate Oil Change? |
|---|---|---|---|---|
| Splash | Many horizontal 4-stroke | Crankcase reservoir | Dipper splashes oil | Yes |
| Pressure | Some 4-stroke | Crankcase reservoir | Pump circulates oil | Yes |
| 2-Stroke Mix | 2-stroke | Mixed with fuel | Fuel/oil passes through crankcase | No (oil added to fuel) |
Practical Tip:
For splash and pressure lubricated engines (four-stroke), regularly checking the oil level and changing the oil according to the manufacturer's instructions is vital. Running an engine with low or dirty oil is a leading cause of engine failure.
Understanding the lubrication system helps in performing the correct maintenance to keep your small engine running reliably.
