O ring on countershaft output. 500/550+

[Seabeowner]

This came up on another site.
It's part no 27 on this link
 https://www.cmsnl.com/honda-cb500k1-four-england_model14660/partslist/E16.html#results

and part no 40 on this link.
https://www.cmsnl.com/honda-cb550k-1978-usa_model7222/partslist/E++15.html#results


This O ring is on many Hondas of the time I find...but I don't think it's on mine! just looked at a spare engine I have and can't find it. It appears to go between the double bearing on the drive side and the oil seal, or maybe just sits on the shaft behind the sprocket. Or maybe the other end of the shaft?

Can someone enlighten me and what is its purpose? Thanks

[paulbaker1954]

Don't remember finding one on my K0 when I rebuilt it if that's any help

Certainly been running fine for a few thou miles and no oil leaks from this area

[paulbaker1954]

Thanks Ken
Didn't replace the bearing sonexpains why I didn't spot it

[Seabeowner]

Yes thanks Ken. I've never attempted to replace that bearing.
Someone on the US site just stripped the lower crankcase off his engine when he found he had that O ring left over in a gasket set. I still don't think he is any the wiser even now! Someone should tell him..(I'm not a member)