Topic: CB125S O-ring Between Cylinder and Head Question

[natez]

When I tore my cb125s down, I removed the head and noticed that the O-Ring that goes around the locating stud/Cylinder stud on the forward/right cylinder head stud was missing, this was the first time I have tore this engine down so whoever did before me obviously left it out. (engine ran fine, no leaking at all without it)

On my new chinese 200cc cylinder, I noticed that there was no space for the o-ring like there was on the old cylinder...

So do I need that O-ring? do I need to have my new cylinder machined a bit or should I just put it together as is? Oil flows up that stud into the head correct?

See attached picture.

thanks!

[eigenvector]

Yeah it's there for oil flow into the head.

Does it need the o-ring?  Hard to say, depends on how good a seal there is between the oil passage and the valve.  If you have the ability to machine a place for it - do it.  It's there for a reason.  Without the o-ring you might get oil leakage back down the passage and less oil up into the head.