The above picture is from Mike N's 503 rebuild. Note the different muffler used by the 503. He also shared the picture below on how to hold the tracks together for splicing.
Barrie writes about the sprockets above:
I hope you enjoy the attached photo. These are a set I made for my
machine (just in case needed). There are four total. The one with the
large hole is for pressing in the two bearings while the other one has a
key cut into it for the front axle. I am not ready to make hundreds of
these yet. I can do the rubber part but the metal flanges are another
story. Once the flanges are set into the rubber , the total thickness
is supposed to be the same as an original. The flanges are riveted or
bolted together through the rubber core. This set was a colaboration
between myself and a tool and die guy from Michigan. They look very
original and should last much longer than the originals since they are
solid rubber...no vulcanizing.
Gary S writes about this sprocket above:
I also had the typical Drive sprocket issue with mine. So I developed my own from a sheet of 1" thk hyfax material which I had machined to the correct profile. Created my own hub using an existing toothless sprocket that I had. It works great and much more durable that the original. The only thing with mine was the hyfax I had was white (and free to me so I couldn't be choosy) so I tried painting it to make it less noticeable, but it didn't really work.
Drive sprockets between the 500 & 502/3 are different. The sprocket hub for the 500 is 1" wide and the 502/3 have a 1 1/4" wide hub. Must have been an upgrade from 67 to 68/69.
I got an excellent question from Ken P up in West St. Paul, Manitoba. He asked about the Idler Sprockets and noted that the cogs are not squared off on each side like the Drive Sprockets are and wondered how they are supposed to mount. I never really gave it much thought, but after searching through my spare sprockets, look what I found:
This is a new sprocket and the directional arrow very clearly shows the sprocket turns toward the beveled edge. Problem is, once you wear in the new sprocket a bit, the arrow gets worn off too. Thanks for asking the question Ken. We all learned something here.
The bearings used in all the Idler Wheels are 6203-2RS which are sealed on each side.