Radius Washer for crankshaft?

[MEASURE TWICE]

http://racing.briggsandstratton.com/videos/maintenance-repairs/proper-clutch-installation

I looked at this video on racing engines, but I expect that the crankshaft on my old Briggs's 3 and 3.5 hp do not need a radius washer between the crankcase wall on the crankshaft and the clutch or sprocket if no clutch used.

There is no bevel to the end of the crankshaft on the engine I have.

I attached picture of video at 1:14 of the 3:01 end minute mark which shows a racing engine crankshaft.

At 1:12 there is the picture of the radius washer that must be used with a crankshaft like this.

The other is my engine with no bevel.

What is the need for a bevel, if I right that must use a radius washer, on a racing engine?

Why bother making a crankshaft that needs an additional part when other engine do not do this like on my old engine?

 

[MEASURE TWICE]

Pictures of both crankshafts 3hp & 3.5hp Briggs show that there is a bevel on them next to the shoulder by the crankcase wall. The 3hp has two bevels, but only the one closest to the crank surface is what contact the gear or pulley. Taking a closer look at the gears that can be mounted with set screw either inboard or out board has the surface also beveled in the opposite direction so I would suspect no radius washer needed. The Pulley has only one side with a bevel edge and the opposite side is where a shaft end bolt and washers are recessed so no bevel necessary.

What is it about the racing engines that they state needs a radius washer, I'm not sure as I have not seen the clutch that they intend on putting on the crankshaft. Maybe it does not have a beveled edge. Then the use of a radius washer should have one side beveled and one side not beveled to make the most contact of surface area.

Why a clutch would not have a bevel to match the crankshaft I have no idea if what I am thinking is true.