There's been some oil seal talk recently, particularly about the cam shaft seals, and I realized I really didn't know too much about oil seals in general. So I decided to educate myself, which proved quite easy. One simple Google search turned up all the relevant info. Oil seals have a code number, usually stamped right on them, that gives the seal type and size. The 1st entry in the code is the seal type and consists of 1 to 3 letters. The numbers following are the size, in our case in MM (I.D. x O.D. x thickness). Determining the 650 seal types and sizes proved pretty easy because they are listed in the earlier factory parts manuals, so I made up a chart ..... Now let's talk a little about seal types. It was pretty easy to find well illustrated info on that. There are as many as 5 different types used on the 650 engine. Some types changed when seals were updated so you may not find all 5 on your particular machine. Most of the seals are the "SD" type, with a sprinkling of "SO" and "SDD" types thrown in. Here's cross sectional drawings of the various types ..... And here's a little tidbit of info about the "SD" type I found interesting, highlighted below ..... Looks like I'll be packing some grease into them before install from now on. Maybe it will help them seal better, and I certainly don't see it hurting anything.