Hi David,

You're only looking at a simple low pressure static seal so as long as the O
ring is compressed when the 2 halves are bolted together you shouldn't have a
problem. If you make the diameter of the recess slightly larger than the outside
diameter of the O ring and, if it's a 0.070 section ring (1.78mm), make the
depth between 1.3 and 1.5 mm, you should be ok.

3/16" seems a bit small for a low pressure return, could it be a pressure feed?

John

--- In halfinchlivesteamforum@..., david_steam <no_reply@...>
wrote:
>
> Ok I will come clean, its for a Royal Enfield 250 cc engine. The two crankcase
halves have a 3/16 passage for (I think a low pressure return) are just butted
together with a bit of sealing gunge and no gasget. So what type of material and
what size and depth seating do I need?
> David
>