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Mechanics Corner: Grease gun type is only half the story

Doyle Schwisow and Lynn Jaynes Published on 24 September 2015

Manual, battery-operated, air-powered or AC electric grease gun – what’s your preference?

On a recent online ag forum, members chimed in with their experiences and advice on battery-operated grease guns.

Pros

Users of battery-operated grease guns seemed to think they were easier to use over manual grease guns most of the time, great when lots of grease was needed and better in tight spots since no pumping action was required, and they have shoulder straps and other accessories to help keep both hands free.

Cons

Not everyone on the forum was a fan, and some preferred manual grease guns. As with any battery-operated tool, there could be potential for battery charger problems. One forum member indicated he’d had trouble blowing seals out of bearings with it, and another complained it was a “bear to get re-primed if the last person just keeps pulling the trigger after it’s empty.”

Options

Yes, you can grease every zerk with a manual pump just fine, but the idea behind battery-operated guns (as with air-powered guns and AC electric or corded guns) is to work smarter, not harder. There will be tight spots and various circumstances where one style will work better than another.

grease guns

We’re not here to sell you on any style of grease gun. We could talk all day about different models, manufacturers and personal experiences, but what we really need to talk about are the options.

Briefly, manual grease guns are actuated with lever action and can achieve pressures up to 10,000 psi. Battery-operated grease guns minimize operator fatigue (no pumping required), are rated at 6,000 to 10,000 psi and generally come in 12-volt, 18-volt and 20-volt varieties. Air-powered grease guns use compressed air and are rated up to 6,000 psi. AC electric (or corded) grease guns are rated up to 7,000 psi.

Technique

Each style of grease gun (manual or otherwise) is capable of several thousand psi per stroke, and it only takes around 500 psi for a lip seal to fail. So the truth is you can blow a seal out of a bearing with any style of grease gun. A ruptured lip seal then allows water or dirt to enter the bearing housing, which will reduce the life of the bearing.

Let’s face it, anybody in a hurry can screw up pretty much anything, and being in a hurry and applying quick, hard pumps with a manual grease gun can do as much damage as an alternately powered grease gun. A hurried approach is a recipe for over-pressurized and over-lubricated equipment.

How do you know that you’ve over- greased? Grease guns can produce between 1 and 1.5 grams per shot. Unless you know what output the gun has, you can quickly over-lubricate a point. There’s a simple calculation that can be used to anticipate how much grease should be used:

G = 0.114 x D x B

Where G equals the amount of grease in ounces, D equals the bore diameter (in inches) and B equals the bearing width (in inches).

Besides being a waste of grease, over-greasing equipment leads to higher operating temperatures. If a bearing cavity has too much grease, it will churn the grease and try to push it out.

This leads to heat, which causes separation of the oil from the thickener. Eventually, the heat cooks the grease thickener into a hard, crusty buildup, which blocks new grease from reaching the bearing core. Thus, over-greasing eventually leads to under-greasing.

For feed trucks and loaders, if you’re greasing them once a week, plan on using one tube of grease per machine if using a manual grease gun. If you’re using a battery-operated grease gun, plan on using one to one-and-a-half tubes per machine, per week.

When you pump grease into the tie-rods or universal joints of a feed truck, you may see a little grease come out of the rubber gaskets that carry foreign material, like dirt or water, and that’s a good thing. These trucks work in environments with a lot of opportunities for foreign material to be pushed into the bearings.

These heavy-duty joints are made so it’s okay to push out foreign material when it’s greased. The auto-lube systems that are now built into forage harvesters have bearings specifically made so it’s okay to push out foreign material during lubrication.

Timing

And let me guess – you’re probably using the grease gun first thing in the morning before you head to the field, right? After all, you pulled out of the field quite late and were tired and ready to get to the supper table. That’s part of your problem. Too many operators try to use cold grease on a cold bearing, and that’s when seals blow.

If you’ll take a few minutes at the end of the day to blow off the dirt from the machine and grease it when the machine is warmed up, the new grease will melt and flow through the bearings for more even lubrication.

Or wait until you’ve used the machine a few hours in the morning to warm it up before you stop and lubricate it. Of course for larger bearings, like the cutter head on a forage harvester or a kernel processor, you’ll end up stopping at least a couple times a day to re-lubricate it.

And if you remember nothing else from this article, remember this: Clean off the zerk before you hook the nozzle of the grease gun to it. If you don’t, you’ll just end up pushing that dirt into your bearing. It’s quick, it’s easy and the decision to clean or not clean the zerk is a bigger issue than deciding what kind of grease gun to use.

If you’ve ever whacked your thumb

If you’ve ever whacked your thumb with a hammer (and that’s pretty much all of us), then this section is for you. Let’s quickly review some practical tips.

  • Never, ever (not even when you feel invincible) reach over, under, through or across moving equipment parts to lubricate equipment.

  • Keep your feet on the ground for stability. Don’t perch or teeter precariously in odd positions to reach a difficult spot. Put a longer hose on your grease gun if you need to reach tough spots, but keep your footing and balance solid.

  • Turn the power switch off before inserting a battery pack, and the battery pack should be disconnected from the grease gun before changing accessories or unscrewing the grease cylinder. Yes, I know, you shouldn’t need to be reminded of this, but guess what? We’ve all done stupid things.

  • When not in use, keep the battery pack away from metal objects (nails, screws, coins or what have you) that can make a connection from one terminal to the other.

  • Use only hoses specified by the grease gun manufacturer and rated for your grease gun. The hose may fail if it is used at an unapproved psi level.

Now go find a rag to stick in your back pocket so you can clean off those zerks. FG

Doyle Schwisow owns Doyle’s Farm Service and has 40 years of experience in servicing farm and dairy equipment.

PHOTO: There are several grease gun options, including manual, battery-operated, air-powered and AC electric. Photo courtesy of Lynn Jaynes.

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