Bearing heat from grease

Submitted: Friday, Feb 01, 2013 at 18:27
ThreadID: 100308 Views:5039 Replies:12 FollowUps:21
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A simple short question, if over-packing bearings causes them to run hot, why do boat trailer bearings that can be pumped full of grease not over heat from the grease ...
Been meaning to ask it for a while now..
Cheers
Joe
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Reply By: Michael ( Moss Vale NSW) - Friday, Feb 01, 2013 at 19:53

Friday, Feb 01, 2013 at 19:53
I would like to know that myself Joe!! And those piddly little wheels are really rotating at a much higher speed than the tow vehicle! Michael
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Reply By: Bob Y. - Qld - Friday, Feb 01, 2013 at 19:56

Friday, Feb 01, 2013 at 19:56
Joe,

Got few thoughts on this. A lot of boat trailers would only travel <100 kms down to the boat ramp, before being immersed in the briny, and cooled down. Then they would sit near the ramp for the day, and back home. Being full of grease stops the ingress of water, so the integrity of the bearings is preserved.

With other trailers, the preload of the bearings would be more important to prevent overheating, along with the required amount of grease to lubricate said bearing. Too much grease would be better than not enough.

I do 4400kms /week towing trailers, and it's scaring when you happen to check the hub temperatures........sometimes too hot to keep your hand on the hub.

Wonder what others think?

Bob.


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Follow Up By: olcoolone - Friday, Feb 01, 2013 at 20:14

Friday, Feb 01, 2013 at 20:14
Bob...... A hub temp that may be hot to the human feel and mind doesn't mean it is hot, you can get 3rd degree burns at 50 deg.C.

Some low temp plastics start melting at 165 Deg C and oils and grease can be stable to 200 Deg C...... Rubber from about 230 Deg C.

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Follow Up By: Bob Y. - Qld - Friday, Feb 01, 2013 at 21:00

Friday, Feb 01, 2013 at 21:00
Good point about the human feel, Olcoolone. Never thought of it that way, always thought if it was hot to touch then must be ready to "spit the dummy".

When you think of it, these trailers go from Brisbane to Darwin, @ 90 clicks flat out, then back again in about 90 hours, with only a few hours to cool down in Darwin. This time of the year they don't cool down much!!! Rarely have a bearing failure........

Remember swimming in a turkeys nest once, with water flowing in from a bore above 50'C, and I thought I'd nearly scalded my, err.........umm, never mind.

About the packing of grease in hubs, the Toyota manual for 75 series definitely said to only fill F & R hubs 3/4 full. As said elsewhere in this thread, anymore would be a waste of grease anyway.

Bob.

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Follow Up By: Member - Joe n Mel n kids (FNQ - Friday, Feb 01, 2013 at 22:09

Friday, Feb 01, 2013 at 22:09
yes Bob i see your point but a lot of boat trailers do very long distances also and they survive, i know people put them on camper trailers also and they do it hard .... and packed chock full of grease .... the rest of the comments are a very interesting read eh ..
Cheers
Joe
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Follow Up By: Bob Y. - Qld - Friday, Feb 01, 2013 at 22:34

Friday, Feb 01, 2013 at 22:34
Yeah Joe, was wondering about all those boats on trailers that pass through Winton every year heading for the barra country, when i wrote the reply.

Don't seem to see too many of them by the side of the road, eh? But seems to be a fair swag on old 'vans & box trailers that have a leg in the air.

Maybe it all comes done to regular maintenance?

Good thread, Joe.

Bob

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Reply By: olcoolone - Friday, Feb 01, 2013 at 20:04

Friday, Feb 01, 2013 at 20:04
I don't know the truth with over packing wheel bearing causing them to run hot....... if you can pack a boat trailer bearing and hub full of grease with no problems then there is your answer.

To little grease can make them run hot, we use just enough grease as there is no point in putting more in and the grease can't go anywhere.

Never heard it a trade school.

If anything more grease will transfer heat to the hub more efficiently....... but a hub should not run hot, if they do run hot it means there excess s friction being generated.

The only thing I can think of is maybe expansion blowing out the seals in the olden days, how seals are designed and the amount of expansion to blow them out I would doubt it.

Me think urban myth.....
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Follow Up By: Member - Joe n Mel n kids (FNQ - Friday, Feb 01, 2013 at 22:10

Friday, Feb 01, 2013 at 22:10
yep i agree ... a myth so it seems eh
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Follow Up By: Member - Frank P (NSW) - Friday, Feb 01, 2013 at 23:19

Friday, Feb 01, 2013 at 23:19
There's a good point here about blowing seals out and the amount of grease in the hub.

I've experimented with a couple of types of seal on my off road caravan. One was an industrial/agricultural seal with seven internal sealing lips, internally lubricated and absolutely bullet proof. It wouldn't let anything in, but nor would it let anything out. The seal retailer suggested packing the hubs with lots of grease to help heat transfer.

My caravan has electric over hydraulic disc brakes. What happened was that when they heated up, as disc braked hubs do, there was little airspace in the hub to absorb expansion and the seals popped partway out of the hub. Not particularly reassuring. I then removed the excess grease to more conventional amounts and had no more problems. They were an excellent seal but I was always worried about the pressure inside hot hubs and the possibility of popping a dust cover or a seal.

The other type of seal was a marine type seal used by the caravan manufacturer. The design of this seal allows it to "breathe out" if pressure builds up inside the hub, but not to "breathe in" if a partial vacuum builds up as the hub cools down. So you can have a hub pretty hot from braking on the way down to a creek, then enter the water and not have it sucked in as the hub cools. (Common sense applies here - let things cool down before going swimming in deep water)

Regarding normal running temperature, I think it depends a bit on load and adjustment. My caravan has a tonne on each wheel. The bearings are large, nominally 3 tonne rating. After hours on the freeway (no braking) they are warm, not hot. You can comfortably hold them tight with your hand. They are adjusted so there is just detectable play when they are hot.
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Follow Up By: Member - Frank P (NSW) - Friday, Feb 01, 2013 at 23:21

Friday, Feb 01, 2013 at 23:21
PS My experience is with trailers and vans. Don't know anything about 4WD hubs as my tug has sealed bearings.
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Follow Up By: Member - Joe n Mel n kids (FNQ - Friday, Feb 01, 2013 at 23:38

Friday, Feb 01, 2013 at 23:38
interesting point Frank P about your pre-load, i had an old merc years ago and the front bearings were set to "end float" NOT pre-load, i asked and old bloke why and he explained that when hot and running with metal expansion they went from end play to no end play, perfect running condition i guess as no play and no pre load ??
And yes i also have had seals pop out from overpacking grease ..
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Reply By: Ross M - Friday, Feb 01, 2013 at 20:06

Friday, Feb 01, 2013 at 20:06
Joe.
I like your reasoning. Apparently some people believe too much grease will overheat the bearings on a 4wd but not on a boat trailer. Strange isn't it.

Most boat trailers with the grease reservoir which pumps/hold grease pressure seem to last and they may leak/seep a bit of grease unless the seal is kept in good condition by replacement at service time.

On a 4wd if you put in too much grease it usually finds it's way out of the hub through the seals and can drip off.

I always fill cruiser hubs so the level is above the edge of the two bearing cups, so when hot, the grease can flow through the bearing rollers and lubricate them.

Less grease means no flow through the rollers and the rollers squeeze the grease away and then they run metal to metal with little or no grease, then they get hot or worse.

Some cruisers from the factory don't have much grease in the bearings at all, some have done wheel bearings shortly after being purchased new.

I know of one new cruiser which didn't have enough and the dealer greased them shortly after purchase. The problem was the person doing the job tightened the bearings too much and the hubs got hot from being tight. Iif driven more than 4 km they got hot. If on a trip, goodbye wheel bearings or worse.

Grease and correct adjustment is ok though.

Ross M
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Reply By: Wilko (Parkes NSW) - Friday, Feb 01, 2013 at 20:41

Friday, Feb 01, 2013 at 20:41
Wondered about this myself as I now put bearing buddies on my work trailer. It sometimes takes a dunking into slurry on minesites. I give them a squirt of grease after every trip and check them regularly by touching the hubs after driving for a couple of hours

It Must be an Urban myth.

Cheers Wilko
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Reply By: disco driver - Friday, Feb 01, 2013 at 20:44

Friday, Feb 01, 2013 at 20:44
If you look closely at a boat trailer hub, the seals are often put in back to front.
This enables the seals to keep the water out rather than keeping the grease in.
That's why boat trailer hubs are filled with grease, the excess will push past the seals as necessary.

Disco.
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Reply By: Gronk - Friday, Feb 01, 2013 at 20:45

Friday, Feb 01, 2013 at 20:45
Greasing of bearings can get very technical.......at work, with large electric motors, we have tech blokes come in and use vibration monitors and can tell if a bearing needs 1,2 or 3 pumps of grease... !!! but will also pickup if the bearing has been overgreased..

Now, for a trailer, it isn't this technical, and overgreasing isn't really a problem, as the large area around the bearings means the bearing itself doesn't get "pressurized" with grease....although (except for boat trailers, when water exclusion is the aim of the game ) you don't really want to fill up the cavity with grease, because 1. it's a waste of grease and 2. the grease won't flow anywhere ( unless it's overheating )

All bearings should only be lukewarm to touch ( unless the brakes have been operating ) in ideal conditions..

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Follow Up By: Rockape - Friday, Feb 01, 2013 at 21:11

Friday, Feb 01, 2013 at 21:11
Gronk,
Sparkies had 2 ABB motors at work. 1 to 2 grams a month all good, over that the motors would alarm at 80c and then shut down at 90c on over temp. They were also labyrinth seals, so there was no restriction on the grease spilling out.

Very important as they were the main pump motors.

RA.
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Follow Up By: Bob Y. - Qld - Friday, Feb 01, 2013 at 21:15

Friday, Feb 01, 2013 at 21:15
Gronk,

That's real high tech, eh!

Back in another life, we were running a small Cat elevating scraper for 6 years. The small elevator rollers, about 150mm in dia, that adjusted the tension on the chains, used to regularly pop a seal or even had bearing failure. Turned out we were pumping too much grease into them(twice/day) so reduced greasing regime to once/day, and only one or two pumps. No more dramas.

Bob.

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Follow Up By: Rockape - Friday, Feb 01, 2013 at 21:30

Friday, Feb 01, 2013 at 21:30
From someone who used to grease every idler every day on a dozer before the advent of sealed rollers, I reckon we should never grease anything.

Only ever pumped enough in to make sure it pushed the dirt out.

Bob! stop polluting our bore water. Ha.

RA.
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Follow Up By: Member - Joe n Mel n kids (FNQ - Friday, Feb 01, 2013 at 22:13

Friday, Feb 01, 2013 at 22:13
i worked with a sparky years ago and i remember him telling me that they were taught to only ever pack them to no more than 30% of there capacity or they will overheat ... it is simply due to the very high revs of an electric motor, a wheel on a car revolves very slowly
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Follow Up By: Rockape - Friday, Feb 01, 2013 at 22:59

Friday, Feb 01, 2013 at 22:59
Joe,
good point and very true compared with a wheel bearing.

RA.
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Reply By: SDG - Friday, Feb 01, 2013 at 21:10

Friday, Feb 01, 2013 at 21:10
Are all the newer vehicles/trailers still using the greasable type of bearings, or have some of them gone to the sealed units?
Only reason I asked is that when I replaced the bearings on my bike a few months back, they were sealed, and I believe I can change a few other bearing over to the same.
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Reply By: Member - Ed C (QLD) - Friday, Feb 01, 2013 at 21:48

Friday, Feb 01, 2013 at 21:48
Here's what the folk at Timken have to say about it >>

"A very high percentage of all bearing damage can be attributed to inadequate
lubrication. Although a very broad term, inadequate lubrication can be
classified into eight basic categories:

• Overfilling
• Underfilling
• Incorrect grease
• Mixing greases
• Incorrect lubrication systems and intervals
• Worn-out grease
• Water contamination
Debris contamination

Overfilling
Overfilling a bearing with too much grease can cause excess churning during
operation and high temperatures, resulting in overheating and excess grease
purging (leaking) – see note below. Overheating occurs because the heat
generated cannot dissipate correctly, continually building until damage occurs.
As the operating temperature of the bearing rises, the oxidation (breakdown)
rate of the grease sharply increases – doubling every 10° C (18° F)."

And>>

"Required Grease Quantity
To avoid the generation of heat, the bearing must not be over greased.
The required quantity of grease is based on the free volume of the bearing
calculated as follows: V ˜ p/4 (D2 – d2) (T) – M/A"

Source>> http://www.timken.com/EN-US/products/bearings/productlist/roller/cylindrical/Documents/BDABrochure5892.pdf


I'll take their word for it ;-)


:)


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"He who lie underneath automobile with tool in hand,
....Not necessarily mechanic!!"

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Follow Up By: olcoolone - Friday, Feb 01, 2013 at 22:06

Friday, Feb 01, 2013 at 22:06
I think they may be talking about force or pressure fed bearing assemblies.
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Follow Up By: Member - Joe n Mel n kids (FNQ - Friday, Feb 01, 2013 at 22:17

Friday, Feb 01, 2013 at 22:17
all was good until i got to your .......
""calculated as follows: V ˜ p/4 (D2 – d2) (T) – M/A""""
........ part and i gave up hahahah
But from reading all the threads i am thinking it is very relevent to the rpm of the bearing, even they say "overfilling" yet a bearing buddy fills them as full as you could ever get ...... all interesting to me
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Reply By: AlbyNSW - Friday, Feb 01, 2013 at 22:32

Friday, Feb 01, 2013 at 22:32
Not an answer to your question but when I suggested to my mechanic to fit bearing buddies to my boat trailer he did not recommend it.
He said that you are better to just pack the bearings correctly, the problem with the bearing buddie type product is that when you pump excess grease in you blow the back bearing seal out and that allows water ingress .

Sounded like a feasible explanation to me.
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Follow Up By: Member - Joe n Mel n kids (FNQ - Friday, Feb 01, 2013 at 22:42

Friday, Feb 01, 2013 at 22:42
Actually no..... as you will read above one says they seem to fit the seals backwards .....
A "Marine" seal that is supposed to be fitted with a bearing buddy is designed to relese the grease pressure but keep out the water, they are a different design to a normal seal .........
He is correct to a point if you fit the bearing buddy and DONT replace the seal you WILL blow out the seal and it will get full of dirt and water and probally only last 1 trip .....
after reading all the comments i would fit em and keep them as full of grease as you can, full of grease = no water can fit ...
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Follow Up By: AlbyNSW - Friday, Feb 01, 2013 at 22:57

Friday, Feb 01, 2013 at 22:57
Ok Thanks
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Reply By: Member - Joe n Mel n kids (FNQ - Friday, Feb 01, 2013 at 22:36

Friday, Feb 01, 2013 at 22:36
Thanks heaps for the replys all, it has been a question i have wanted to ask for a while as i have read many threads about bearings and packing them and most go on about "over-filling" them as a big issue, i now think it may well be a myth, yes the factorys only put a dash in these days but that may also be a cost cutting process also, they would use 5 times the grease if they filled them i guess ......
My thoughts now are it depends on the RPM of that bearing, in a high RPM bearing you can NOT fill it more than 30%, in a low RPM such as a wheel you can fill them, my thoughts now are to fill them as full as i can, it will help with water ingress as there simply is no room for water to get in if full, it is very low RPM si it will probally assist with getting rid of heat and i am now thinking it is the brake heat i am feeling as it is bolted right up to the hub and they get REALLY hot and the heat will transfer to the hub as it is bolted to the disc ...
I have often wanted to put a grease nipple on my hubs and give them a couple of squirts every trip, 2 years ago i had a dry bearing squeaking and got to it just before it failed and came apart, at Wycliff Well actually, pulled it apart and it was dry as a ..... and black and burnt, i cleaned it up as best i could and packed in the grease, re-assembled it with very light per load, picked up a new set of bearings at Tennet Creek and decided it drove well, was still reasonably cool, same temp as other side, and was to bleedin hot outside so we just drove on, drove from there all the way home to Doomadgee and ended up replacing it 6 months AFTER we got home and it was still blackish but well greased and lot no pre load ....
All bearing failures that i have seen and had were dry of grease, some with muddy water ..... never have i seen a fully packed bearing fail, on a car anyway ...
So i am gunna pack em as full as i can get from now on and see what happens .... keep in mind if you pack the free wheeling hubs full they wont work mmmm bugger maybe just lock em im an leave em ....
Thanks all, very interesting reading....
Myth is "busted"
Joe
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Follow Up By: Member - Joe n Mel n kids (FNQ - Friday, Feb 01, 2013 at 22:55

Friday, Feb 01, 2013 at 22:55
now all of this has me thinking ......
We have a problem up north in the really hot places with water getting in the fuel of small equipment .....
The cause .... the fuel tank sits in the HOT sun, the air expands and vents out, it rains and rapidly cools it down, sucking in air and at the same time ... water .. as it is raining ....
A gearbox in a 4wd has the exact same problem, you are screeming along the road, gearbox it boiling hot and air is thin hot and most expelled out the vent, you hit a crossing and imerse that gearbox in cold water, the air cools rapidly and sucks in water in the vent, same in diffs, stinking hot and dunked in water, sucks in heaps of water ....

Soooooo my hubs will be stinking hot as i have jammed on the brakes for the crossing, in go the red hot hubs into cold water and any air space will contact and suck in water ....

So keep that bearing jam packed full of grease just like a bearing buddy and the water ingress will be 1/8 of what it was, all makes sense now .. :-)

If you want an example, get a 20 drum and take off the lid, heat it up (safely) and when all the air inside is hot whack on the lid and hose it with cold water, it will thrink and actually CRUSH the drum ....

Cheers
Joe
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Reply By: pop2jocem - Saturday, Feb 02, 2013 at 10:34

Saturday, Feb 02, 2013 at 10:34
And then of course there is the subject of oil filled instead of greased wheel bearings, but I guess that is a subject for another day (;-))

Cheers
Pop
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Follow Up By: Member - Joe n Mel n kids (FNQ - Saturday, Feb 02, 2013 at 10:46

Saturday, Feb 02, 2013 at 10:46
you probally remember the thread about it, tried to do it on mine but impossible ........... but another day eh
Cheers
Joe
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Follow Up By: Axle - Saturday, Feb 02, 2013 at 14:19

Saturday, Feb 02, 2013 at 14:19
Funny you should mention that pop!,....With a landrover you have the best of both worlds, the inner axle seals always leak so you have grease and oil in there!....some just remove the inner seals all together and let the oil in, just change the hub seal from a grease one to a double lip oil seal and bobs ya Uncle..lol.


Cheers Axle.
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Follow Up By: pop2jocem - Saturday, Feb 02, 2013 at 16:58

Saturday, Feb 02, 2013 at 16:58
Hi Axle,

Could just be another viscous malicious rumour started by them Toymotor Missan mobs but I have heard from my BIL'S mate's cousin that Landrovers also have their own built in anti-rust and dust suppression systems....hehehe. Not to mention an automatic oil draining program.


Cheers
Pop
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