How to avoid excessive lubrication of needle roller bearings?

Using too much grease to lubricate needle roller bearings may cause serious complications in the machine. During operation, the accumulated grease in the needle roller bearing chamber begins to agitate. If the grease is sufficiently stirred, it will rapidly oxidize (chemically degrade) as it begins to lose base oil, becoming thicker and less lubricated.

The thickened grease can also be pushed out of the cavity and distributed throughout the windings of the rotor assembly. Operating temperature increases with little or no lubrication, leading to seal collapse, needle roller bearing failure, and energy loss. Excessive heat will eventually "burn" the remaining grease, thickening it into a hard, crustlike solid that is difficult to remove, preventing any new grease from reaching the needle bearing core and accelerating wear of the rolling element.

In short, the real dangers of overlubricated needle roller bearings are complete machine failure and expensive equipment downtime. Another negative consequence of overlubrication is increased pressure. Lip seals tend to fail at about 500psi, so any additional pressure from the grease gun (up to 15,000 psi) can cause lip seals to break, allowing contaminants to enter the needle roller bearing housing. Increased pressure can also cause hard, scabbed grease to break, directly into the needle roller bearing track, leading to accelerated wear and ultimately to overall failure.