Topic: CB125S O-ring On Bottom of Cylinder

[natez]

Last question I think...

On my old cylinder, there was a thin O-ring around the barrel recessed into the cylinder. It was recessed so far I would be surprised if it actually sealed anything up. On the new cylinder, there is a slight recess, but this time it barely fits half the O-ring in it if that. Needed?

eigenvector you will probably say the same here as the other O-ring, but I just want to be sure.

I'm using cmsnl.com for a parts fiche, it shows the O-ring, but doesn't have the part listed on the parts list...(http://www.cmsnl.com/honda-cb125s-1978-usa_model414/partslist/?model_q=cb125s)

[eigenvector]

Honestly I have no idea what that gasket does - probably there to pick up any slack between the sleeve and the case. 

It's not like there's any room for oil to work it's way up between the sleeve.  It isn't preventing compression leaks.

I'm sure someone who knows more can explain the purpose.  My guess, it just helps the base gasket do its job better.

[natez]

I took a second look and on the new cylinder, the o-ring only fits about 1/3rd into the shallow recess...

[eigenvector]

I'd shy away from using it then.  The last thing you need is an o-ring squishing out and mangling the bottom gasket seal.  It was crammed up into the groove on the old one because the head was torqued down quite a bit.  I would hesitate if there was any chance it was going to prevent the base gasket from sitting flush.