To grease or not to grease...........

[GKQ]

While using the excavator the other day at a friends we got into a debate over, over greasing bearings.
I say just do as the manual says, he says grease is the cheapest metal, ie greasing saves replacement. So looking up various paperwork/reports on the net both sides have positives and negatives.
Over greasing actually pulls dirt in to bearings, and the extra grease causes it to fly out of the bearing when running, leaving a 'dry ' bearing vs over greasing pushes dirt out and extra stops bearings running out of grease.
Having just re-done 20 odd bearings, now I'm sitting on the fence.

What's your take on the matter ?

Graham

 

[Pete.]

I've heard some good ones in my time but I never heard that greasing a bearing causes a dry bearing. Who dreams up that sort of crap?

 

[brianblock]

Regular greasing actually pushes the dirt out of the bearing

 

[Johnseat]

Constant flow of fresh grease keeps the dirt out if the nipple is cleaned before filling.
Also the extra grease around the bearing encases the bearing in a water proof and dirt proof grease casing.
Under greased bearings will fail prematurely, I've done a paper on the life expectancy of bearings over a period of years for my hgv Apprenticeship.

 

[octo0072000]

go with the grease i never heard of grease causing a dry bearing

 

[Rig Pig]

I would always over grease rather than under grease, then again my kit runs in cold damp conditions intermittently, the fresh grease pushes water (and the shotblast that gets generously spread everywhere) out of the pivots and bearings, in all honesty in most applications the extra grease forms a larger seal unless the bits are flying round. A quick stroll round with a grease gun is going to add hundred of hours life.

 

[GW8IZR]

Well then, over greasing an axle box causes the grease to shear rather than lubricate, over greasing axle boxes causes hot axle boxes which causes derailed trains.

 

[Pete.]

Over packing an axle box might cause extra heat but not over-greasing excavator arm bushes. I say that if you haven't had any squeeze out you haven't put enough in yet. The only problem with over greasing bushes is snot dollops and wasted grease. You can over-grease a hammer though.

 

[Badger1bear]

As everyone else has said, bushes on an excavator cannot be overgreased, it will force out solidified grease and crap and replace it with clean. This needs to be done more often when working in submerged water conditions.

 

[GW8IZR]

The point I was making is that the OP's research might not be so misguided, to say over greasing can't cause dry bearings is incorrect and certainly not 'crap dreamt up by someone'

Whatever we all think we know, bearings should have the correct amount of the correct type applied at the correct interval, and more isn't automatically better.

(edit) cos I think we are at cross purposes here.. if you google over greasing bearings you will find factual data that over greasing bearings is detrimental, I think its probable that this is the data the OP has found, its not 'crap' but its not applicable to a slow moving bearing of the type he is dealing with.

 

[Hood]

The point I was making is that the OP's research might not be so misguided, to say over greasing can't cause dry bearings is incorrect and certainly not 'crap dreamt up by someone'

Whatever we all think we know, bearings should have the correct amount of the correct type applied at the correct interval, and more isn't automatically better.

That is certainly true, especially of higher speed bearings. As an example spindle bearings in a machine tool can fail very fast if they are overloaded with grease. I think it makes the balls slide rather than roll and produce a lot of heat.

 

[Badger1bear]

When it comes to excavators we are not talking high speed precision bearing or in the case of the working arm there are no bearings it's "generally" pins and bushes. A pin/bush or bearing can't be left dry because excess will be pushed out but still leaving the remaining grease that is from where it entered the pin/bush bearing at the grease nipple. Surely to end up with no grease in a bearing you would need to force air through to move out the residual grease leaving it empty ????

 

[Rig Pig]

The boom pins and undercarriage on an excavator aren't high speed or precision, they spend a lot of time submerged in water and mud, if the grease is not regularly washed through then expect large repair bills. Obviously the slew bearing and any winch bearings are a different kettle of fish.

 

[Hood]

I should have only quoted the second part as that was what I was replying to, not the dry part although overheated grease may turn to liquid and run out with the excess heat.
Yes for an excavator it is a different story, however I remember a boat I worked on would chew through bearings on the trawl winch, eventually after 4 or five replacements in a year the skipper got in touch with the manufacturers. They asked how often we greased it, every day said the skipper proudly. Reduce it to once a week came the reply you are overloading the bearings. It worked, can't recall that particular winch needing bearings again.

 

[dannyp]

a lot of times people don't bother to take the weight off pins and bushes when greaseing them, hence the grease dosent get where it's actualy needed.

heavy slow moveing stuff working in unfavorable conditions most of the time the more grease the merryer. but hardened steel on steel bushes that are desinged to run dry grease dose not help them but rather turns to grinding paste.

on some machenes we build at work, the one of the them that was for ourselves i stripped every roller assembly and overpacked it with grease and thats greatly helped longevity.

with bearings tomuch grease can push the seals out tho, high speed stuff really wants oil. another machene i built for myself ive been useing a bodyjack pump to pump thick oil in them, but in that i'me useing cheep ball bearing inserts working way out of spec but with regular oil they have accseptable life

 

[Robotstar5]

We used to have a company come in to do an annual service on the robots, part of it was changing the almost liquid grease in a couple of geartrains. They originally used a handpump that fitted on the top of a 25 litre drum, but one year turned up with an air powered pump to speed things up, on the first one they did it blew the seals out of the joints, they were there an extra day to strip the robot and re-seat the seals

 

[GKQ]

Right so in a nut shell the general opinions are:
1 bushes slow moving dirt attracting lots of fresh grease
2 fast running bearings follow instructions

I also note whilst reading what does grease bearings mean in relation to quantity of grease? Do you add until it comes out of the bearing seal?
On my tractor mower it just says grease bearings every 8 hours, I just do two or three squirts and hope that's enough. Too much and the seal lifts up and out it comes when the deck is running.

I think this why men don't read instructions, they tell you to do something but not by how much.

Graham

 

[Pete.]

Big end bearings in an engine - not exactly high speed in most cases, lubricated with oil.

Wheel bearings are fairly high speed, they usually get greased.

I think you got that backwards. Big end bearing in a car - max 5-8k rpm. Car wheel bearing typically 1400 rpm @ 100mph

 

[Pete.]

BTW phenolic bushes on our old Belle skid steers = no grease, not grease point to put it in either. Lasted a long, long time under heavy use.

 

[The_Yellow_Ardvark]

I always maintained if it has a grease nipple, grease it until you se new grease appearing.
Kramer front loaders used to have pictures showing how they liked to see grease on a arm pivot etc.

@Pete. I think I know what you mean on a skid steer, (bob cat), my friend has one for mucking out. Has no grease points, they have lasted 15+ years.

To much Grease will not hurt in this case.

I wonder how many people here have watch some one go mad with a grease gun , leaving a ton of grease on the nipple. But none inside as the nipple is blocked.