A planishing broach is a series of increasingly larger smooth round rings on a bar that is pulled through the bushing. May I quote from Broaching Practice
by Edward K. Hammond.
SIZING ROUND HOLES with a Planishing Broach Fig. 6 show how a broaching machine and planishing broach were used for sizing holes in hard phosphor-bronze bushings. This material, as any mechanic who has had any experience with it knows, is difficult to finish-ream. It is tough, elastic and slipery, and the less there is to ream the more difficult becomes the operation. Instead of reaming, the holes are enlarged slightly by pulling a smooth-toot broach through in a regular broaching machine. It will at once be seen that the operation is that of compressing the metal in the sides of the hole until it has enlarged to the finish size. Each of the rounded rings or beads on the broach is a little larger than its predecessor, thus gradually compressing the metal the desired amount.
Full text at http://books.google.com/books?id=a5pKAAA...ach&f=false
This is a similar process Carrillo uses on there steel rods to finish the bronze bushing used in their connecting rods. Sunnen also has a process that adapts their pin hones to burnish wrist pin bushings to size.
But the most common way these phosphorus bronze bushings are sized is with a Sunnen connecting rod hone. Because, unlike a steel rod that can be bent to insure the centerline of the bushing is aligned with the rod's big-end, aluminum rods must be machined square during the refurbishing process. You cannot bend an aluminum rod to align the bushing!!
Because of the nature of most bronzes used for this application they are hard to machine using any form of cutting tool. A reamer, especially a fragile adjustable one, is no exception. And as said above, don't turn the reamer backwards when reaming one of these bronzes or in an instant it will no longer have a cutting edge. It will have to be re-sharpened before it will cut again.
Because of this Triumph always provided the replacement bushings to a finished size - pre-finished. An allowance was made to the bore so when installed the pressure of the press fit crushed the bushing to it finished size. While not a perfect solution, it is a lot better than trying to ream the hole with an adjustable reamer. For a lot of reasons none of the current group of people manufacturing replacement bushings supply them pre-finished.
In short, just because you can buy replacement bushings doesn't mean that you are qualified to install them. This is not a home-workshop job and should be left to a professional. I dare say that few motorcycle shops have the training, equipment to do the job, or the ability or equipment to check their work.
When the bushing is not square to the centerline of the crankshaft bearing you not only cock the piston left to right, you create a little mechanical engine. This little engine drives the wrist pin from one side to the other with each time the rod changes direction. It does this with enough force to cause the circlip to fail allowing the pin to cut grooves in the cylinder. Of course the cocked piston does nothing to help oil control, detonation and the other horrors we see with pistons.