Its a gusher, I struck OIL !!!

[Metal Butcher]

Shown on many plans are oiling points shown as small holes drilled down through the top of bearing blocks. They normally have a larger size countersink at the top to accept a micro drop of oil.

prior to running an engine I applying a very small drop of oil that disappears down these drilled passages.

Now the fun begins! :big: After a few minutes or so of running the oil rises rapidly up the drilled passage and floods the top of the bearing block! ???

Has any one experienced this puzzling phenomenon, or have an explanation for its occurrence?

-MB

 

[websterz]

Thermal expansion. Less room for the oil and it has to go somewhere.

 

[vlmarshall]

A lot of bearing systems use hydrostatic hydrodynamic pressure to float the shaft on oil, I've seen it a lot in turbochargers and turbines. Usually, there'll be a few ramps cut into the bearing surface, to build up oil pressure. Is your bearing bore perhaps not completely round, or several thou larger than the shaft?

 

[vlmarshall]

Kinda like this, only you've got the hole on the high-pressure side.
http://www.stle.org/images/dev/image10.jpg

 

[tel]

I've had that happen, tho' I have no real explanaition for it, other than to note that it seems to occur more regularly with shaft fits that are somewhat toward the looser side of the spectrum. I've always put it down to a bit of air being pushed up through the oil, and indeed, on occasion you will get a little bubble rise and (hopefully) burst. Other times the oil will sit at the elevated level seemingly forever. Shoving a bit of wire down the hole seems to get things going again, or you can increase the head of oil thusly - I rarely see it happen with an oil cup fitted.