Lapping flywheel to crank taper?

[garry-in-michigan]

In the old days before torque wrenches came into use, the service manuals said to put an open end wrench on the flywheel nut and beat on it until it stopped moving. This left great latitude in how tight the nut was. Some compounded the problem by putting oil on the junction, thinking it would make it easier to take apart. Instead it became easier to FLY apart. It wasn’t until Evinrude started supplying outboards to the Military in the early 1940s that torque numbers were specified for the Speeditwin, Speedifour, and Big Four at 75 to 80 Foot Pounds for their Flywheel nuts.

[amuller]

Many small engines that don’t need the flywheel located for timing purposes don’t use a key. The cast iron Kohlers with battery ignition come to mind.

Briggs, at least on the little cast iron engines, used to use soft metal keys.

[fleetwin]

How well I remember those soft metal flywheel keys when I worked on the lawnmower shop as a kid! It was very common for the homeowner to hit something and shear the key causing loss of spark…The nice thing about the Briggs was that shearing the soft key rarely damaged the flywheel or tapers, whereas the Tecumsehs usually wrecked the flywheel when their solid key sheared. Now that most mowers have breakerless ignition, they don’t lose spark when the key shears….So, I’m thinking that many strange running conditions don’t get easily diagnosed.

[billw]

Listen, I’m not an engineer, just a knuckle-dragging boat mechanic. I have lapped MANY a big, inboard propeller taper and I have the destroyed back to prove it. I have never, ever, lapped a flywheel and have also never had one of my properly torqued ones shear or break. This includes a good number of various year Big Twins. I tend to agree that, if West Bend said to do it, they may not have had much faith in the manufacturing tolerances. Just my two cents.

Long live American manufacturing!

[Author]

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