Applying grease is a pretty simple task regardless of whether you are packing a bearing, greasing an axle or swingarm pivot etc.. However there are a few mistakes I see people make that are very easy to avoid. So here is a quick rundown on the proper way to apply grease and the easy things to avoid.
The first thing is to wear gloves if you are going to have direct contact with the grease. Not only is the petroleum not too great for your skin, but many of the additives used are none too friendly either.
Is it going to kill you?
Is it going to damage your skin?
Might it cause skin irritation?
This is more probable, but even so typically not a big deal unless you have very sensitive skin
Regardless of the low chance of damage being done, there is still a chance of damage being done and taking precautions is worth the effort despite the inconvenience. Usually nitrile gloves are pretty easy to come by in large packs and they are resistant enough to give you basic skin protection.
If you do get grease directly on your skin, it is a good idea to wash it off as soon as you can to limit exposure. It certainly isn’t convenient, and I rarely follow this piece of advice myself. However, it is still a good idea.
The second piece of advice is; do not over-grease! I see this mistake probably more than anything else. More is not better and too much grease can be worse than not enough grease sometimes. The idea of grease is that it gives a solid film that a bearing or shaft can roll over. If there is too much grease packed inside a bearing, the bearing’s rolling elements will have to push through the grease rather than roll over it. This churning through the grease causes overheating, accelerated oxidation and will often cause the oil component of the grease to bleed out. If the oil bleeds out you are left with a hard, brittle mass of thickener that makes for a poor lubricant.
Another possibility depending on just how much grease is in there is that the rollers in a bearing may not be able to roll properly and they end up sliding rather than rolling. This sliding friction causes more wear than rolling does and the ball or roller ends up wearing very unevenly and causes flattened surfaces to form and exacerbate the condition. The end result of all this is a bearing that has its life severely shortened due to excessive or abnormal wear.
Just as too much grease is bad, too little is also detrimental to bearing life for more obvious reasons. Under-lubrication results in overheating, excessive wear and deformed parts due to those two things combined.
There is a relatively easy calculation based on a formula attributed to the bearing company, SKF. Take the bearing diameter in inches multiplied by the width of the bearing in inches and divide that number by ten. It is not the precise formula they developed, but that is an easy way to do it without having to break out a calculator in the garage and should be close enough (the exact calculation divides by 8.772 if you want to be precise).
This calculation using inches as the measurement gives you ounces of grease needed when re-greasing a bearing. Just remember that it is inches and ounces; it won’t be the same calculation for other units of measurement.
For other applications like chassis pivots and axles, usually just a smear of grease is what I was taught long ago and I’ve never seen anything to contradict that; so until I hear otherwise, I’ll keep doing and recommending that. I’m pretty sure excess gets pushed out when refitting the rod into the sleeve again anyway.
If you are applying grease using a grease gun through a zerk grease fitting, not over-pressurizing the bearing is crucial. Common grease guns are capable of producing several thousands of pounds per square inch(psi) of pressure and common bearing seals are usually fail at pressures under one thousand psi. There are several tips when using a grease gun that can save you from a lot of grief later on.
- Know how much material the grease gun delivers per stroke and meter your input to the recommended amount.
- Pump the grease slowly to build pressure slowly rather than quickly to distribute grease evenly and avoid rapid over-pressuring
- If you feel an abnormally high amount of back pressure, stop. That back pressure should signify either the cavity being full or an obstruction that may need fixing.
- Know how much material the grease gun delivers per stroke and meter your input to the recommended amount! (Yes I said it twice. It’s just the best practice in my opinion)