Belgian1979 wrote:When you have two circles that intersect, you have a very limited contact patch at the area where they touch. In a plain bearing, this contact area is a lot bigger. So the actual contact area in a needle bearing depends on how many needless you have around the axle (and the diameter of axle versus the diameter of the needles). So the diameter of the axle is a factor here as you can fit more needles around it.
In a typical u-joint the axle is big, the needles small so a lot of needles present to distribute load. The axle in a lifter is a lot smaller.
If a lifter comes off the lobe, and is then pounded back into it, the needle will cause an indentation in the surface. Next time needles go over that indentation you get vibration.
First, there is no intersection,; it's called tangential contact and the amount of contact is defined by the design.
Like Warp Speed has said many times, the dynamics of a U-Joint cannot be compared to those of a lifter.
The size of the axle lifter is defined and chosen by the manufacturer and it varies from manufacturer to manufacturer.
In what surface would the needle cause an indentation? Vibration?
It boils down to the design of the lifter, the materials selected and the type of needle bearing selected.
If a manufacturer chooses and inferior bearing, expect a failure.
Turbine engines have needle bearings in all the rotating assemblies.
Their rotating internal speeds in their second stage, depending on the engine are from 12000 to 24000 RPM's constantly during operation.
Just imagine the loads and beating these bearings take during a 12 hour flight, several days a week or during the year.
They also run very light synthetic oils at operating temperatures exceeding 500 degrees C.
Turbine engines also have more operational loads and vibration when compared to a race engine.
Guess? Those needle bearings run for thousands and thousands of hours without failures.
Also, it is interesting why Jesel doesn't offer a bushing lifter.
If they were so great, they would offer one.
In my book, only Jesel and Morel are the lifters to use if you want reliability.