[wiekingderviking]

I have the right side engine cover off in order to deal with the leaking kickstart plate/seal (I've cut a GASKET for it, drilled the 4 mounting holes larger, and spot-faced each hole to prevent the screw heads from limited positioning of the plate, and installed a new seal).

 While the cover is off, I got to thinking about the  quality of the sealing that should occur between the oil pump OUTLET (via an "o-ring" seal) and the oil filter INLET hole that is in the right side cover. The "o-ring" is actually a quite hard nylon or polyethylene material, not very resilient, flat on the backside.

It seems to me that it is pretty much by chance that the pump OUTLET will seal POSITIVELY to the oil filter INLET when the right hand cover bolts are cinched up (variables may include: "o-ring" thickness; side cover gasket/sealant  thickness; cover bolt torque; side cover distortion hot versus cold; etc.)

Has anyone experimented with a REAL o-ring instead of the nylon? seal?
Other fixes? Opinions?
Some folks will probably reply, "just assemble the darn thing and hope!" The trouble is, the lubrication of the whole engine relies on the integrity of this OUTLET to INLET seal!

 I was blissfully pleased with the design of the new UCE engine until this puzzle came to mind....

[gashousegorilla]

  Yes.... you can definitely use an O ring.   That "seal" you mention is just the flattened stock O ring .   It flattens out after assembly... and can get hard over time.  I replace that O ring , or at least inspect it when ever I pull a right side cover off.   To keep it in place during assembly, I coat the O ring in a healthy slathering of Grease .

[Haggis]

Yep, as GG says they regular O rings. Yours are just a bit tired. I do believe that they are a service item ? Time or milage? I can't quite recall.
Don't forget the other seal that keeps the oil going to the crankshaft.
OIL SEAL, CRANKSHAFT OIL FEED
Code: 500622
Price: £7.70

[gashousegorilla]

     I have been using a P10A   or  9.8 x 2.4 mm over the years without a problem.  I suppose a P9 would work as well.  It IS a very tight fit in there once everything is buttoned up.  And YES... I DO have an oil pressure gauge and everything is fine.    A shot of the O ring in question ... before and after.

[jefrs]

O-rings are as cheap as chips. You probably want silicone because they're heat proof and oil proof, but they can be softer, if it's a stationary seal no problem but might want nitrile (oil proof) where stuff rotates.
RE are metric but there are still a couple of imperial Whitworth still on the bike. The UCE should be all metric.
Some of the grooves RE cut can be too deep for the O-ring they fit. The one on the EFI suction filter plate didn't seal and wanted a thicker 30x3mm there
I'm thinking a 10x3mm should be the correct size here.

[Arizoni]

I do not recommend using silicon o-rings for any location where gasoline or oil is present.

The simple Silicone rubber (red color) is not compatible with motor oil.
Parker, one of the largest makers of o-rings says under its silicone rubber listings,

Not compatible with:
• Superheated water steam over 121°C (250°F).
• Acids and alkalis.
• Low molecular weight chlorinated hydrocarbons
(trichloroethylene).
• Hydrocarbon based fuels and oils.
• Aromatic hydrocarbons (benzene, toluene).
• Low molecular weight silicone oils.

Nitrile (Buna N) has very good oil resistance up to 250°F but it does lose strength above that temperature.  As oil temperatures in a air cooled engine can exceed that amount, materials with higher temperature ratings are preferred.

Flurosilicone (FVMQ) works well with motor oils and its temperature rating is good up to 350°F.

Fluorocarbon rubber (FKM, Viton) is excellent with motor oils and fuels and it is rated up to 400°F. (Usually very expensive.)

[grey pegasus]

The last post concerning this topic was already some time ago, but probably some new ideas are welcome.
I modified my oil pump outlet with a stud that reaches inside the oil filter compartment. A nut on the stud compresses an o-ring that is placed inside the oil filter compartment and seals the joint.

[Haggis]

Is that not the low output pump from the 350?
High output pump looks like,