Briggs & Stratton Model 95902 Recoil Starter Cog-And-Ball Clutch

I've coined the term 'cog-and-ball' for want of a better name for the clever little clutch in the recoil starter of a Briggs & Stratton Model 95902 vertical shaft lawnmower engine.

This type of clutch is all but trouble free, and likely to last forever. There is a limit, though, to how much neglect it can take, and the one in my old Sears Craftsman 20" mower reached its limit this spring. The clutch still engaged and worked for starting the engine, but upon starting I'd get a dreadful shrieking noise, and the starter's pull-cord would vibrate violently between the handle and the starter housing. I surmised that the cog-and-ball clutch was perhaps binding slightly and causing all the noise, and so I decided to open it up for a look-see.

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First off, the cowl with the recoil cord/pulley has to come off. There are three obvious 1/4"-20 x 1/2" hex head screws that hold it on. A 7/16" socket wrench is needed.

That gets you to where you can get at the screen over the flywheel.

Remove the two screws with a 1/4" nutdriver, and you have access to the clutch's dust cover/seal.

Hold down the centre spindle while you pry up the dust cover with a pocket knife blade, and you get to see inside.

And there we have what I call a 'cog-and-ball' clutch. With the engine stopped, the balls are free to roll down their ramps to where they meet their central cogs. When the starter cord is pulled, the clutch's central cog spindle jams one of six balls up against an outer cog, and so can turn the flywheel. Once the engine starts, centrifugal force sends the balls up their ramps and into their pockets until the engine is stopped.

 The central cog spindle rides on the upper end of the crankshaft, and it must freewheel smoothly without any binding, else you get the noise and vibration effects that I was getting. Clean the spindle's bore and the upper end of the crankshaft. (Mine was fouled with gummy old lubricant.) There's what I take to be a lubricant wick up inside the bore of the cog spindle. Give that a good soaking with WD-40, reassemble the works and you're good to go. Spray some WD-40 around the lip of the clutch cover's seal. Use no grease inside the clutch; nothing must impede the free motion of the balls up and down their ramps.

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Note that the lower/outer portion of the clutch is also the flywheel nut on this engine. To get it off, restrain the flywheel, and crank the clutch portion off in the normal direction with a big pair of Channellocks. Mine came off easily. Here's a view of it removed and off to the side.

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