Idea for sealing valve guides

[gbritnell]

In this hobby the biggest use for O rings I suspect is for piston rings. While one can argue the success of this type of usage the design intent of O rings isn't made for this type of application. To generally be affective O rings need some type of compression to create the seal between the shaft or surface they are being used for. For reciprocating or rotating shafts the surface finish must be smooth enough to not abrade the O ring yet not so slick as to cause the oil to wick past the interface. In the case of using O rings for valve seals I'm sure it would work but with ever so slight variables in O ring sizing (past discussions on using O rings for piston rings) trying to get just the right fit in such a small diameter would be painstaking.
As far as my engine smoking from top end leakage it has to be realized that the area under the rocker cover is bathed in oil as is it's full sized counterpart and even with tight tolerances between the valve and guide there is still that small clearance for the oil to be drawn past, especially when there is a vacuum applied.
It's nice to have conversations like this because with enough responses you get to find out what successes, or failures, others have had with certain components.
gbritnell

 

[mu38&Bg#]

The MC14E engine is interesting. I don't ride, but my buddy does and has never brought this engine to my attention.

That reminded me of the little Honda GX25,31,35,50 utility four stroke engines. The GX-25 parts list shows a stem seal on the intake valve only. The stems in the GX-25 are 3.5mm nominal. What is the scale of your parts?

3D pdf files are large and the viewer is slow. I have it in SW, but never use it. SW eDrawings is much better, and has more functionality for the viewer.

Greg

 

[Jordan]

There are many examples of oil control for inlet guides only. My AJS has an adjustable needle valve - just for the inlet. Even with a flooded rocker box, I'm thinking exhaust gas pressure should be greater than gravity?
For long term use an O-ring might not be best for dynamic applications. But it does work, until it wears out. Smooth surfaces definitely a help to reduce abrasion.

 

[johnny1320]

One problem I can see is then you have over head cams and you are running bucket followers the pumping action under the bucket could force oil into the exhaust and intake past the guides, even the hot exhaust will make it smoke and I am wondering if this is part of Keith5700's problem.

 

[Jordan]

I'm not clear how a pumping action would happen in that scenario. I guess it could pulsate, but nett effect would be neutral.
Provide a passage between spaces above and below the bucket?

 

[johnny1320]

I'm not clear how a pumping action would happen in that scenario. I guess it could pulsate, but nett effect would be neutral.
Provide a passage between spaces above and below the bucket?

Would not be neutral, if oil gets under bucket it will try to compress and will pressurize the under side of the bucket, on a large engine where there are large areas for the oil to go but on a small engine not so much. I build 600hp dragbikes all bucket tapets.

 

[Jordan]

OK, I just remembered I've never had bucket tappet experience.