What Are the Symptoms of a Thrown Rod in a Riding Lawn Mower?

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Riding mowers need regular maintenance to operate properly
Riding mowers need regular maintenance to operate properly (Image: lawnmower man image by feisty from <a href='http://www.fotolia.com'>Fotolia.com</a>)

Many different problems can befall a riding mower. A belt can slip off or the mower deck can get out of level. But by far the most terrifying and expensive for the homeowner is throwing a piston rod in the mower motor. If you suspect that you may have thrown a rod, immediately stop the mower and turn it off.

Smoking Exhaust

If the mower's exhaust is emitting a dark blue or black exhaust smoke, stop the mower. Allow the mower to cool off for an hour or so and check the oil. If the oil has turned black, it may indicate a thrown rod. Smell the oil. If it has a burnt smell then a rod is thrown. It may not be completely off of the rocker arm, but it is holding oil and burning the oil inside the piston chamber. This can lead to an oil fire or even an explosion if the mower continues to run.

Mower Will Not Stay Running

If the mower will not start or starts and then immediately stops the piston rod may be disconnected from the piston. The mower needs the pressure that builds up in the piston chamber to keep running. If this cannot happen because the mower has no pressure, it will stop. If allowed to run in this condition it will eventually lock up the engine which will lead to expensive repairs.

Extreme Banging from the Engine

When the mower engine is making a loud banging sound this is the easiest way to know that you have thrown a rod and pushed it through the piston. Imagine hitting a cast iron skillet with a hammer and you can hear the same sound. If you hear this, stop the mower immediately, as the rod can eventually come loose and go through the piston head becoming a very dangerous projectile. If this is happening, there will also be a leak of oil through the seals on the piston cover.

Ways to Avoid these Problems

Check the oil before every cutting. The main reason a rod is thrown is because of a lack of oil on the piston head. When the piston head becomes too hot it will seize the engine and cause the rod to break off inside the piston chamber. Have the mower examined at least twice a year. Simple diagnostics by a trained professional will reduce the possibility of an interior problem. Change the oil and the oil filter (if the mower has one) at least every 40 hours of use. Dirty oil can also cause a piston to seize.

References

  • "Riding Lawn Mower Service Manual: Volume 2, 1992 and Later (Riding Lawn Mower Service Manual),"; Primedia Business Magazine Media, 2001
  • "How to Repair Briggs and Stratton Engines, 4th Ed.,"; Paul Dempsey; 2007
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