Most people hate lawnmowers. Mechanics certainly do. Only the Brits, who race them for big money, care about them. Syd hates them more than most, because he has a huge lawn and his wife is forever trying to increase its size. To top it all, last week the mower stopped, refused to run and Syd couldn’t find out what was wrong.
He was mowing a fairly new section of the lawn when the cutting blades hit a partly-buried stone and stopped because the impact sheared the key securing the rotating blades to the output shaft.
The engine also died, which was not unusual under the circumstances, so Syd removed the blade assembly and tried to run the engine on its own just to make sure there was no internal damage, but the engine refused to run.
It started first pull on the rope, but died almost immediately. It had been running well just before the incident and sounded healthy enough when starting, but Syd could not figure out why it would not keep on running.
“Oh, to heck with it,” he said, or stronger words to that effect, and put the thing away until he felt like looking at it. The next day, at the lunch break under the old tree, Syd regaled us with his latest lawnmower saga.
We were cruel enough to laugh, but the incident set my mind going. I ‘phoned a friend who sells lawnmowers and solved the mystery. Some lawnmower engine manufacturers rely on the cutting blade inertia to augment the flywheel inertia when doing their calculations.
This means the engine won’t run without the cutting blades attached because there won’t be enough flywheel-effect. Syd scoffed at this theory, but when he replaced the key the engine ran perfectly.