NotTaR of small Gasoline Engines and Rotary Lawn Mowers : Stopping the engine                     
 Copyright © 1994-2007, Samuel M. Goldwasser. All Rights Reserved. Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied: 1. This notice is included in its entirety at the beginning. 2. There is no charge except to cover the costs of copying. I may be contacted via the Sci.Electronics.Repair FAQ (www.repairfaq.org) Email Links Page.

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Stopping the engine

On most inexpensive lawn mowers manufactured within the last 10 or 15 years, releasing a dead-man bar on the handle both kills the engine and applies a brake to the blade (well, actually the flywheel of the engine). In this case, there is nothing to think about - just release the handle and it will stop within a second or two. These are quite reliable. The usual problem is that you forget to engage the dead-man bar and attempt to start the mower despite the basic fact that this is quite impossible!

More expensive equipment will have a blade brake clutch meaning that while there is still a dead-man bar but instead of killing the engine when released, it disengages the blade (clutch) and brings it to a rapid stop (brake). This is more convenient especially with a balky engine. There will then be a separate engine stop switch - possibly combined with a speed/throttle control.

Equipment with an electric starter may have an ignition switch just like an automobile and there will be three positions: STOP, RUN, START.

Some older equipment just has a stop contact that grounds the spark plug. Pressing on a lever connects the spark plug terminal to the engine chassis and kills the spark. While this is fairly reliable, it may be a momentary contact meaning that the engine may be on a hair trigger and even rotating the blade a fraction of a turn may cause the engine to take off again. Thus, disconnecting the spark plug wire or removing the spark plug is even more critical when working on this sort of equipment.