Topic: Purpose of "O" ring fitted to bottom of Cylinder sleeves

[CB750F2]

What is the purpose of the 61.8x2.0mm "O" rings fitted over the bottom of the cylinder sleeves of the CB 750s? What holds these "O" rings in place? Would it be a good idea to "cement" these in place with threebond 1104? Thanks, Pat

[scunny]

not sure about the 750 but the 650 has a groove to sit the O-ring in.
I think(dangerous) it's to stop oil travelling up outside the sleeveand under your head gasket

[754]

Did Honda cement them in place??

I am sure the Honda engineers considered the job it has to do when the determined the specs for the chamfer they sit in.. pretty sure they know how to build an engine.. so do what the manual says..

Generally an o-ring provides a seal to prevent leaking.. tolerance are calculated and parts machined so that the chosen o-ring will do the job

[CB750F2]

Ok. I am finding it difficult to seat those "O"rings properly in their seat so I am going to machine a sleeve that will fit over the sleeve to make the job easy. Thanks for your replies and help. Pat

[754]

I think assembling the moyor is what seats them..

[Cvillechopper]

I prefer to have them seated prior to assembly just to make sure you don't have a twist (potential leak).  those o-rings are pretty durable.  Once I have them on the sleeve, I roll them as far down as I can get them use a small, flat plastic blade on each side between the ring and the sleeve to "pry" it down.  Rotate the position of the blades and go at it a few more times and PRESTO, they're seated.  At least that's how I get it done and i've not had a leak yet.

[Big Jay]

Never really understood what they were trying to prevent. When big bore sleeves are installed, there is no o'ring and no leaking.

Jay

[mattcb350f]

it's to stop oil travelling up outside the sleeve and under your head gasket

That's what I've been told too.

[Bob550four]

this is Honda folks.  they have a big habit of OVER engineering something like this to prevent issues as best they possibly can. 

It's built like the manual says to build it because an engineer years back designed it, probably tested it 20000 ways from sunday, then tested some more to ensure it works 10000%   why change that?