Sunday, May 29, 2011

Small Engine Smarts: The Five Basic Systems, Part 2

Image by David Reber's Hammer Photography

Previously, we took a look at the fuel system and the compression system. Now let's go over the three remaining of the five basic systems:

System 3: Ignition
System 4: Lubrication and Cooling
System 5: Governor (Speed Control)

The ignition system is how your small engine starts. It can be a manual start, meaning you have to pull on a rewind or starter rope in order to turn the engine over the first time and start it running. Or it can be an electric start, which means that it has been equipped with an electric starter motor and a key, and all you have to do is turn that key to crank the engine up. Machines with electric start engines will generally have a higher price point than those without. 

The initial tug on the starting system, whether provided manually or electrically, causes the flywheel to turn. The flywheel has magnets mounted on it, and as the flywheel spins past the ignition armature, an electrical flow will occur and produce a spark at the tip of the spark plug. The spark, which is timed with the motion of the piston and the valves (part of the compression system, remember?), will then ignite the air-fuel mixture in the combustion chamber. Once you give the engine that initial spark, its own momentum will keep it spinning and running.

Common Parts of the Ignition System
  • Spark plug
  • Spark plug wire
  • Ignition armature
  • Flywheel
  • Flywheel magnets

Lubrication and Cooling
You've certainly noticed that your engine gets hot when it runs. Though some of that heat escapes through the exhaust gases and radiant heat, much of the heat remains in the engine. And overheated engine is an engine that won't keep running long, and that's why lubrication and cooling are so important. 
Oil is the lubricant which keeps engines cooler by reducing friction between the various engine parts. Friction is a major source of heat, so the less friction produced while an engine is running, the less heat. (Note: this does not mean that you should dump in more oil than recommended for your small engine! Excess oil does not mean less friction. Follow the guidelines in your owner's manual.) 
Air is the other cooling component in an engine; you'll notice, on the outside of the engine block, ridged cooling fins which increase the surface area of the engine so that more engine is exposed to more cool air. Keeping the cooling fins clean is an important part of maintaining your engine. 

Common Parts of the Lubrication and Cooling System:
  • Oil reservoir
  • Dipstick
  • Oil dipper or paddle
  • Oil filter
  • Bypass valve
  • Cooling fins
  • Flywheel fins
  • Blower housing
  • Air guides

Governor (Speed Control)
The governor system allows you to use your power equipment under different loads while keeping the engine running at the same optimal speed. For a mower, the load would be how high and thick the grass to be cut is. The higher and thicker the grass, the more of a load the engine is under to move the machine and spin the blades through it. The governor automatically notes changes in the load as your machine encounters them, and adjusts the throttle so that the engine runs optimally without you have to make manual adjustments while you work. 

Common Parts of the Governor System:
  • Engine speed control
  • Throttle lever
  • Governor spring
  • Speed control cable
  • Throttle linkage
  • Governor lever
  • Governor cup
  • Governor shaft
  • Flyweights
  • Camshaft
  • Timing gear

Arco Lawn Equipment provides how-to articles, advice, and all information on this website for informational purposes only, and cannot be held liable for damage to self or equipment incurred. Please read your owner's manual, follow all safety instructions, wear proper safety apparel, and never allow children or pets to play in or around lawn equipment. Consult a professional small engine technician if you are unsure about any of the steps involved in power equipment maintenance, use, or repair.  


  1. To get the best service we have to follow this instruction.If we follow this strictly we will be able to get the best use of any kind of small engine.We can also use this Briggs and Stratton Parts in our engine.

  2. I searched the Web and then I found this very comprehensive guide. Thank you so much for taking the time to share such helpful information.