Wrist Pin Oiling Question

[olddog]

I got to thinking about how the wrist pin gets oiled, and was a bit dumbfounded as to how that little bugger survives.

Unless I missed something, I have never seen a wrist pin getting pressurized oil from the pump. I recall a hole in the piston for splash oiling, but don't remember if that was a lawnmower or a car engine. I suppose the rings scrape oil off the cylinder walls in the general area. So how do they get oil?

They carry the same load as the rod journal, yet are much smaller in diameter. I realize they only rock back a forth and do not see the high differential speed in surfaces as the rod journal does. It just seems to me these guys are in a very tough environment, without a lot of oil flow.

[Rick Parker]

Most OEM applications utilize splash lubrication for this. Some high end rods and manfacturers have a very small (EDM) hole that runs lengthwise in the rod from the upper bearing saddle to the wrist pin bore in the rod. Pressurized oil is then carried to the upper regions of the pin bore. Some also have squirters that direct pressurized oil from the lower regions of the block to the bottom of the pistons in an effort to cool them but some splash provides a lubrication source also. Sometimes there are also gooves machined in the wrist pin bore in the piston that carries oil scraped by the oil rings from the cylinder walls. Either way it does a tough job that is often not given much thought.