rear case inserts

Above you see the inserts from a 420 auto and an insert from an 1985 to 1988 two stroke standard shift engine. Does anyone care to comment on an engineering reason for the diameter being a few thousands less near the flange. Let's say I got new one and covered it in a layer of bronze and then turned it down to just a little bigger to match what I bored out the rear of the engine to (or what the size of the hole is) is there some reason to copy this feature?

Fran

The guy who was turning it down realized he was screwing up and opened up on the diameter. Then he said "O'what the heck, it will still work" and threw in the box.
Being silly here, no idea.

when they were originally installed, they heated the cases, and dropped them in, after the cases cooled, they shrunk around the bushing.
these wearing out, breaking, pounding out, seizing ect, are a common issue .
heres some fixes iv done in the past.
when retro fitting a 86 510 into a 81 Auto , i had to trim the shoulder, and installed oil light bronze bushings,,,they never worked loose.
on a 86 400 WR i had some pound out the cases a bit...this was back in 1988, i used a good epoxy, and basicly glued new ones in place..guy still owns my old bike, and they have never came loose, or gave him an issue.
a few years ago, i had some crack, i made a set from 6061 aluminum, epoxied them in place as well, they worked awesome...
i have a 430 with loose bushings right now, the best way i can see to fix them is to turn a set from oil light bronze over size, so that they fit tight, and press them in place.
oil light is self lubricating, and will keep the swingarm pivot bolt from getting rusty, crusty, and loose.

We have a winner! This is exactly right and there is a service bulletin about the turned down diameter under the flange.