Thread: Too much bearing grease?

Admittedly all my experience is with wheel bearings on 4WD's but I don't believe you can put too much grease into a bearing - any excess will find its way out and simply fly all over.

If its a roller bearing assembly then could the bearing and race be nipped up a tad too much, causing friction to generate the heat?

If its a plain roller bearing is the spindle spinning too fast for the type of bearing?

Surely if those bearing units come with shields, they were pre-greased. When you say you filled them, was that until grease oozed out of the shields? That would be 100% packed. Imagine the balls and the cage trying to push through a solid wall of grease, thats going to take some energy.

What sort of speed are we talking here? 3,600?

Regards Phil.

Originally Posted by ventureoverland

Admittedly all my experience is with wheel bearings on 4WD's but I don't believe you can put too much grease into a bearing - any excess will find its way out and simply fly all over.

Not sure I've ever seen shields on any wheel bearing that's regreasable, I though that was what the grease cap was for. To collect the excess.

You do know on something like a landcruiser 285/65 R17 tyre. The circumferance is close to 2.5m. They do 660 rpm at 100 kmh.

Grease comes in two parts, a lubricant and a filler. The lube is a light or medium high spec oil, and the filler will be some kind of soap and/or lithium compound. For a high speed bearing you need just enough grease to provide a source of the lube which bleeds out of the filler onto the running surfaces. It should not churn around in the bearing and produce heat and drag.
Even the lower speed wheel bearing is initially packed full between the rollers but the cavity between bearings is only one third full to allow the surplus to rapidly migrate and just provide that reserve of oil lube for the contact surfaces.
Once made the mistake of lubing gears and bearings of a heavy angle grinder with a very tacky grease of the wrong spec and it would not attain more than half speed and was overheating. Wash it out and start again!
Those sealed bearings with nipples sometimes come with the instruction to re-lubricate sparingly once per year or 5000 hours.
Worth a look at an oil company's application guide. You will find near a hundred greases for a myriad of applications, one size don't fit all.
Combustor.

Originally Posted by ventureoverland

Admittedly all my experience is with wheel bearings on 4WD's but I don't believe you can put too much grease into a bearing - any excess will find its way out and simply fly all over.

If its a roller bearing assembly then could the bearing and race be nipped up a tad too much, causing friction to generate the heat?

If its a plain roller bearing is the spindle spinning too fast for the type of bearing?

It's a ball bearing unit, self-aligning (so that's not an issue), and rated max speed is over 6,000 rpm, more than twice the actual spindle speed.
I thought the grease would melt and drip out, but this isn't happening apparently. I don't have it with me, as it's in my friend's workshop so that's just what I'm told. I'm going to have to go over to check it out.
Thanks,
Jordan

Originally Posted by Machtool

Surely if those bearing units come with shields, they were pre-greased. When you say you filled them, was that until grease oozed out of the shields? That would be 100% packed. Imagine the balls and the cage trying to push through a solid wall of grease, thats going to take some energy.

What sort of speed are we talking here? 3,600?

Regards Phil.

Speed is the same as motor, which is around 3,000 rpm.
I'm thinking like you - too much grease, as I did indeed fill them until it oozed out, to make sure it had enough!
Hopefully it'll fix itself, if it eventually melts.

Thanks, Jordan.

Thanks for your thoughts too, Combustor.
I fear a disassembly, clean out and sparing regrease is needed.
To bad the bearings didn't come with instructions.
But, I'm sure I've packed bearings to the hilt before. Maybe not for relatively heavy duty and high speed though.

Jordan

Jordan,

In SKF's Bearing Maintenance and Replacement Guide of 1986, under Requisite Grease Quantity is this -

Where no recommendations are given, the quantity of grease to be used can be calculated from the equation

G = 0,005 D B

Where

G = grease quantity, grams

D = bearing outside diameter, mm

B = bearing width, mm

Bob.

Originally Posted by Anorak Bob

Jordan,

In SKF's Bearing Maintenance and Replacement Guide of 1986, under Requisite Grease Quantity is this -

Where no recommendations are given, the quantity of grease to be used can be calculated from the equation

G = 0,005 D B

Where

G = grease quantity, grams

D = bearing outside diameter, mm

B = bearing width, mm

Bob.

So for a 50mm x 10mm bearing G = 0.005*50*10 = 2.5 grams. three parts bugger all... so, don't overgrease.

Ray

Yoiks! That explains it.

Thanks folks,
Jordan

I had read that when bearings are over packed with grease, the grease gets too hot and the oil drains away from the filler. This leaves the filler caked inside the bearings with no effective lubrication. The bearings then fail.

I too struggle with knowing the right amount of grease to pack. The posted equation seems to be a good overall guide.

Simon

It depends on the rpm. At low speeds, you can fill the bearing to 100%, and it will not overheat. Example is a car wheel.

At very high speeds, you cannot use grease at all. You must use oil. The bearing data sheet will tell you for every bearing type and size, what the maximum speed for grease lubrication and for oil lubrication is.

At the top end of the speed rating for grease lubrication, you should not overfill the bearing with grease. Something around 30-40% filling is normal (meaning 60 to 70% of the room between the metal parts remains empty air).

If its bearings that can be heavily pre-loaded (angular contact and taper roller bearings) it is necessary to reduce the grease filling ratio long before reaching the maximum rated speed for grease lubrication, as such bearing can heat up very fast.

What happens when a bearing gets hot because of grease churning when overfilled is this: grease is a mixture of oil and a thickener. When grease is heated past a certain temperature, the oil leaves the bearing through the seals. Leaving the thickener behind. Thickener depleted of the oil is also known as gunk, and its a very poor lubricant.

Regarding the greaseable flange units, are you not supposed to remove the inner shields of the bearings? Anyway, these are supposed to be filled 100% with grease, until the grease exits the shields. And this means they are only intended to be used for low rpm. You can use them for higher rpm too, but then you do not use the grease nipple and either only partially fill during assemble, or use pre-packed sealed for life bearings.

Originally Posted by cba_melbourne

Regarding the greaseable flange units, are you not supposed to remove the inner shields of the bearings? Anyway, these are supposed to be filled 100% with grease, until the grease exits the shields. And this means they are only intended to be used for low rpm. You can use them for higher rpm too, but then you do not use the grease nipple and either only partially fill during assemble, or use pre-packed sealed for life bearings.

The flange units don't enclose a housing. Both sides of the bearings are exposed to air. They are actually extended type.
Good to learn this, thanks.

Jordan

Originally Posted by RayG

So for a 50mm x 10mm bearing G = 0.005*50*10 = 2.5 grams. three parts bugger all... so, don't overgrease.

Ray

Looking at this another way .

Assuming a 50 x 10 mm bearing
- uses 8 mm diameter bearings
- bearings sit in an annular ring 2 mm in from the outer edge of the bearing
- the centre of the bearings are then on a 19 mm radius, 119 mm circumference ring
- this ring will contain ~15 bearings with a total volume = 15 x 4/3 x Pi x 4³ = ~4000 mm³
- volume of cylindrical ring containing bearings;
Outer cylinder = 8 x 23² * Pi = 13300 mm³
Inner cylinder = 8 x 15² * Pi = 5700 mm³
Difference between volume of bearings and volume of cylindrical ring = 7600 mm³
The density of grease is about 0.9g/cc so the volume of 2.5g of grease ~2800 mm³
Packing fraction is thus 2800/7600 or about 35%

This does not take into account the ball groove/recess in the bearing or any retaining rings.