I stole a bearing experts post from a Harley forum, it is worth a read IMO.
By RobertC
On greases and bearings.
Greases have several functions.
Hold the oil in place so it is available to the bearing
Carry additives, such as anti wear of extreme pressure additives. (which, to complicate matters, are sometimes in the oil and not the grease.)
Doing that is rather more complex than it seems at first glance.
First, we need to select an oil voscosity. Yep, not all greases use the same "weight" of oil.
Along with that comes oil type questions.
Then we need to select a thickener.
Lithium
Lithium soaps
lithium hydroxode
Clay of various types
Calcium of various types
Polyureas
and other more exotic stuff.
and then we have the additives. Anti wear, extreme pressure, etc.
So now, we want to pick a grease to top up a cavity.
We need to select a compatible thickener first. Some mixes are compatible, some mixes make a runny mess, some mixes make hard particles that bearings do not like.
hmmm, people complain of runniness. Could mixed grease types be an issue?
Then we need to get the right NLGI grade. 0000 runs, 6 is a brick. 1 and 2 are common.
Finally, oil type and viscosity along with additives
I get paid good money to make these decisions. And they are sometimes quite involved and cause massive headaches.
Now, bearings. I get paid to nurse them along too, I see all of our failed ones, and any others I can lay hands on. I also spec bearing types, fits, lubrication, and other minutae.
Plain roller bearings are packed on installation. Like in our steering heads. This leaves a large space for us to fill. Sucks, but it is reality.
Ideally, on a high speed bearing you want the magic amount of grease, not too full, but enough to transfer some oil. On low speed steering heads, full is ok since we'll never churn the grease here.
You see, on a high speed machine a full bearing and cavity will lead to churning and heat. then failure. It is actually better to undergrease than overgrease a typical electric motor or rotating machine. I can actually pick up overgreased bbearings with my ultrasonics gear. Very distinct sound that your dog can hear quite well. At which point I monitor with vibration instruments until the bearing either rearranges the grease and quiets down or I see early signs of bearing failure.
As for HD cheaping out by not using sealed bearings, yep.
Now, be wary, do NOT EVER grease a sealed bearing. All you will do is ruin it. No matter the machine it is in. You just can't do any good with a grease gun on a sealed or double shielded bearing.
In fact, if you were to redo a steering head and put in sealed bearings you don't need any other grease. Period. And take the zerk out. Any greasing will, once the cavity is full, simply act as a hydraulic pump and push the seals/shield combo against the balls and cage. Toasting the bearing in short order.
As for shielded bearings. If using a single shileded bearing, the open side goes toward the grease fitting, and amounts of grease to add are adjusted down.
Double shielded, pack the cavity 70-80% full and walk away with thwe zerk in your pocket. Adding grease beyond that will end up pushing the shields into the balls. Toasted bearing results. All the lube that bearing ever needs will come from oil seeping out of the grease pack and into the bearings factory grease pack.
I'd guess, as pointed out before, that HD is using open bearing for cost savings. We then pump until grease comes out to flush out crud and water contaminated grease. And to ave HD a nickel.
If, in the next couple of weeks, I can find my special steering head grease gun I will see if my test gear will give me some idea of iots properties. At the very least I should be able to tell the thickener type. Which is, potentially, reason enough to not mix greases willy nilly.
Otherwise, I need to buy new stuff come spring "get ready" time and I'll do it then.
__________________
Lubrication Analyst in a nuclear power plant.
ICML certified Machinery Lubrication Analyst Level III
And some other stuff.
------------------------------------------------------------------------------
