JSharp said:
It doesn't make sense because it's a myth. The first place I heard this "theory" was many years ago when Harley mechanics were blaming their crank bearing failures on synthetic oil, claiming it was "too slippery for the bearings." Of course it ended up being just low quality bearings in the low quality engines they were working with but the myth remained.
Fact is, if there's so little load and friction for a bearing to roll, there's too little of each to do any damage.
The "just touching on a single point" addition to this myth we've seen in this thread to explain further is also not possible. Quality bearings are ground to such precision tolerances that if "a single point" is touching the whole roller or ball is touching. The only way that couldn't happen is if the bearing was such poor quality it wasn't round in the first place.
Well, if it is a myth, then it is a myth that my cousin (by marriage) believes as well. So, why would that be relevant? He is the Quality control engineer and testing branch supervisor for INA / FAG bearings in Germany.
That said, when he took me on the tour of the testing and R & D department, we discussed it at length, and like so many other things the real answer is "it depends"
One of the particular questions I had for him, and we discussed in detail, is our practice of taking the seals off the bearings on our dirt bikes, and packing the bearing plumb full of grease and then popping the seals back in.
We do this, in the thought that it is better to have it plumb full of grease, then to have the customary amount of void or airspace in the bearings.
He then brought up the sliding of the rollers, explained that the type bearings we were using were "stock" or "catalouge" bearings made to fit a wide range of uses and for our particular application it was probably a wise choice. We were probably more likely to experience bearing failure from dirt, crud and water then from the bearing sliding instead of smoothly rolling.
He then went on to point out that those bearings were originally intended for high speed electric motor applications where that small, precisely measured amount of grease was determined to give them their best life for their average expected use.
Then he took me into the room where they were currently running tests to determine optimum lubes, rates, etc. etc. of running bearing's to failure.
So, is it a myth, not in my opinion. Does someone take something out of context and apply it where it should not have, happens often, and as I often say at work, why is it so hard to get out good information while bad information can spread like wildfire.
In the FWIW category, I doubt seriously you could overlube any bearings found on my ag or construction equipment.
I am in the lube it till it comes out, wipe off gross excess yet leave some to form a sheild on open bearings / pivot pins, and on closed or sealed area's try and put a very small amount in till you believe it has recieved grease and not so much as to break the seal.
