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10th Aug 2020, 01:32 PM #16Most Valued Member
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10th Aug 2020, 07:28 PM #17Diamond Member
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Its so you can adjust the end float on a taper roller bearing set. Imagine trying to adjust the wheel bearings on your trailer if the cones were a interference fit on the shaft. On a wheel bearing set that is correctly adjusted the axial load from the nut is enough to stop the inner race from turning on the shaft.
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10th Aug 2020, 10:17 PM #18Novice
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That's great guys - thanks for the replies.
Hehehe I was trying to avoid Loctite if I could - my question was in regard to wheel bearings located within front hubs on a vehicle....... So the hubs are spinning around the stub axle.
My bearing knowledge is limited - that is why I put "single row tapered roller" in the title and not just "bearing tolerances" - I thought this type of bearing was adjustable - i.e. not an interference fit with the stub axle (or shaft or whatever) and its clearance was adjusted via the locking nut?
I did look around for a bit, but from what I observed, their was specifics given for the bearings, but not for the races - i.e. the shaft size that goes in the centre of the bearing was obtainable, but not the size of the hole that accommodates the race for the bearing (which is what I was after) - this of course could have been user error ) but I found this information difficult to find.....
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10th Aug 2020, 10:22 PM #19Philomath in training
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The problem with too tight is that material has to go somewhere. If it is going into a sturdy housing, that means the inner diameter of the outer (the ball race) gets smaller. Too much smaller and the clearance in the bearing is lost. If it is too tight, it is kinder to the bearing to take some material out (assuming you can measure accurately down to the micron level). It does not take much.
Michael
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11th Aug 2020, 09:30 AM #20Mechanical Butcher
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11th Aug 2020, 10:03 AM #21Most Valued Member
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It’s a pair of opposing bearings.
2cups, 2cones.
The cones get squeezed together by the adjusting nut creating the preload that stops them spinning.
Steve
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11th Aug 2020, 07:43 PM #22Mechanical Butcher
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But my Nissan Navara doesn't use pre-loaded wheel bearings. The manual says to tighten but then back off.
In this case I think there's a slight amount of tightness on the shaft.
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11th Aug 2020, 08:34 PM #23Most Valued Member
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I never preload bearings on a vehicle except to seat them, then back off and tighten to allow a thou or two end float. Done hundreds this way and never have a problem. If they are too tight to start with they get hot and don't last long.
Nev.
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12th Aug 2020, 01:28 AM #24Most Valued Member
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I'm not an auto mechanic, but have done a fair few wheel bearings over the years. As you say they don't last long if they are tight enough to make them hot. I find it differs depending on the vehicle and bearings though.
On something like a Falcon with little wheels and tiny bearings of different sizes, if you breath on them hard they will be too tight.
On my Landrovers with 2 large bearings the same size and large wheel diameter they like to have just a very gentle hand tightening on the socket. Definitely no end float, and a bit more hand force if you happen to be adjusting one that still has the wheel mounted as you have to overcome the weight of the wheel that wants to spread the cones due to the roller angle.
An interesting comparison from my past life in aviation maintenance where aircraft wheels were torqued.
Higher torque to seat, back off until the nut was hand tight, then torque to a low setting for preload.
Completely different operating conditions to an automotive vehicle ie only a few minutes slow taxi, high speed takeoff run then frozen for the flight duration, then instant high load spinup on landing, potentially with huge side loads from cross winds etc. They also have the bearings mounted in the wheel itself, so the wheel and bearings get removed and serviced/inspected with a tyre change (which could be anything from 1 to a few hundred landings).
The bearing manufacturers notes on preload/clearance of tapered rollers make interesting reading. More preload gives more rigidity and load carrying capacity, but shorter bearing life. Apparently for best bearing life you want to end up with the zero preload/clearance condition in the normal running condition, but in practice that's not a simple thing to achieve.
Steve
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12th Aug 2020, 02:03 PM #25I break stuff...
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My procedure for wheel bearings has always been to tighten them up fairly hard, give them a good spin to make sure they're seated. Then back them off, and give them a very light nip up. It's very much a 'feel' type thing, but what works as a guide to develop a feel is to set a 16 inch breaker bar up a little above horizontal, and gently allow the weight of the handle do the 'nip up'. You're basically trying to get all of the rollers in the slightest contact with the outer race, as under gravity the inner race tends to drop down a little when you slack them off (meaning that the hub is 'hanging' off the two inner races, and the rollers are not making contact at the bottom). If you can do it with the wheel on, it's much easier to check as you go. You basically just slowly tighten and check until all play at the outer edge of has only just been removed - no more. Don't forget to spin it a few times before you check, as they can seat a little bit when you do this, and get a little looser.
Done it this way with hundreds of Land Rovers, trailers, Fords and various other things. At one stage I was involved in building Group S and club sprint Alfetta racecars, which have the pissiest little tapered front wheel bearings. The front wheel bearings used to go for a couple of years of racing before starting to get a bit rumbly, but keep in mind the whole setup is pretty flimsy, to the extent even on road tyres cornering loads were enough to flex the spindle and cause pad knockoff. The problem was even worse when you started talking semi slicks or full slicks, much left foot pumping of brakes was required down the straight to get the pads back out. We started getting spacers machined to put between the inner and outer bearings, which then allowed us to simply do the retaining nut up FT, and greatly stiffened the whole arrangement with a substantial reduction in pad knock off, which made for much more confidence as a driver. Didn't really change the life of the wheel bearings though, despite probably being slightly less preload than my adjustment method.
But even without the spacers, they handled turn 1 at Phillip Island just fine lap after lap at about 170km/h on semi slicks with that preload setting mentioned, no explosions. We actually used to go through rear wheel bearings at about the same rate, and they were a much bigger and beefier double row sealed ball bearing with no adjustment as you find on many modern wheel drive cars.
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12th Aug 2020, 03:16 PM #26Mechanical Butcher
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I owned some motorbikes with TRBs for wheels.
One was a '50s Matchless, which specified positive end clearance.
Another was a '70s BMW, which was meant to be pre-loaded - ie, no clearance.
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