Join Date: Oct 2013
Location: Chilliwack, BC, Canada
That bearing is a seven ball rather than 8 as one would expect for for a 6204. This will mean a heavier cage or such modification. Likely there were design concerns that the cage would break from vibration... that's what came to mind so started looking along those lines- special bearing.
The quick check I made indicates that this is an OEM manufacture only "S" means special dimensions or features and 37 means that it is the 37th design type used in this bearing series. I will see if can find someone with NTN who is willing to dig to find out the special features of the design. I wonder if the internal clearance is greater because of a larger interference press fit into the case + the heavier cage? I don't recall a locating pin on any of the KLR balancer bearings (to keep the bearing from turning in the case) but forget and confuse with other engines as see so many apart and KLR guts not that frequently. One reference indicated an update of the OEM number from "SX04A37" to "TM-SX04A37" and that "TM" indicates a long life material. The "SX" was last produced in 2006 while the "TM" prefix is still being made.
All I can find but will try the forbearance of NTN to see what else.
FWIW, there's no way I'd use a 6204 in place as have seen this kind of substitution often go bad with other bearings such as a special ball size in the same inner and outer race dimensions. Having a balancer cage fail (the most common mechanical failure to a single row ball bearing, IME) would be nasty as the balls often run over the loose cage pieces and spread the outer race, breaking the surrounding structure.
Can't find anything on the SX0415 but since that's likely the 15th design of the 04A, it may be very old and because the design numbers aren't related to one another, just that they indicate some design change to the basic 04A, it could mean anything.
I'll continue to order those sorts of bearings from Kawasookchi. I think that the bearings inside were ordered by the owner so must be why I don't recall this issue.