I just want to put my rear wheel back on (rear shoes on Mazda 323) and tighten the bearing nut to the right amount. A specialist bearings manual says this:
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1) Tighten locknut to 18-22 ft-lbs/25-29 Nm.
2) Turn the hub 2-3 times.
3) Loosen the locknut and finger tighten.
4) Turn the locknut until torque to turn hub with a spring scale attached to a lug stud is 1.3-4.3 in-lbs/.15-.50 kg.
5) Stake locknut.
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Very roughly, in everyday terms, what force or effort does "18-22 ft- lbs/25-29 Nm" approximate to?
Very roughly, what effort would "a lug stud" pulled by a force of "1.3-
Never mind the "very roughly" - you can get a very good idea of what effort these equate to.
Take say a 4ft length of wood and balance it on another at its mid point above the ground (eg a see-saw). Now stick a sack of 10lbs of stuff (eg spuds weighed on a kitchen scale) on one end. Now see how much effort you need to push down on the free end to get the bar level again. That would be the effort you would need on a 2ft long spanner to give 20 ft lbs. For a 1ft spanner, stick 20 lbs of stuff on the seewaw above and see what effort that takes.
Better - buy/borrow a torque wrench, they aren't that expensive.
For the other, measure the distance from the centre of the hub to the stud. Let's say that is 2". Tie a piece of string to the stud and turn the hub until the stud is at the same height from the ground as the centre. Let's say you are aiming for 3 in-lbs - divide that by the 2" above and that gives a weight of 1.5lbs. Fill a bag with 1.5lbs of stuff (eg kitchen scales, spuds) and tie it to the string. With the locknut finger tight, this weight should pull the stud downwards. If so, turn the hub to get the stud level again and tighten the locknut until the hub just fails to turn under the weight of the spuds.
Or, if you are a fisherman - put a spring balance on the stud and pull downwards (with the stud level with the centre of the hub) until it reads 1.5lbs - assuming 2" distance, as above, that will give you 3 in-lbs. The hub should start turning as soon as you pull harder.
18-22 lbs weight acting on a horizontal 1ft long spanner. Or 36-44 on a 6" long one, etc.
You need to measure the distance from the centre of the hub (in inches) to a wheel stud and then divide that into the 1.3-4.3 in lbs. Then use a spring balance (for weighing fish?) attached to the stud to measure the required pull. Adjust the tightness of the nut until you get the figure you've just calculated.
I used to know a guy who was a specialist pipe fitter. He spent all day torquing up large pipes with flanges on them for all sorts of different systems using air or transporting liquids in places like oil refineries. He was so used to doing this sort of job accurately that he told me he could put wheel nuts on and set them all to the same torque. He did it and I checked it with a torque wrench and he was spot on. Once I saw him put the cylinder head back on a cortina without using a torque wrench and that car ran for many years afterwards with no head problems (it was his own car so he had a vested interest in getting it right). My guess it it was some sort of "muscle memory" effect. I play the trumpet and thats how we can play notes in tune just by tightening our lips. My muscles can remember what they should feel like for the different notes (about 7 per valve combination).
Yes, only if all the involved muscles are in the fingers and possibly the wrist too, but not the whole arm and certainly not half of the body, all at the same time. That's what doing or undoing a wheel bearing nut will involve. The propioceptors in the joints concerned have to be co-ordinated and mapped (memorized and stored in the brain). We know the body can remember a small map -- I know, for I play a string instrument -- but when one half of the body has to be remembered, the map is just too big; the resolution is not fine enough to reproduce the same response time and time again. To demand the precision in doing/undoing a wheel bearing nut repeatedly without error is physiologically not possible.
If the back-street gang is doing this, they deserve to be called "grease monkeys".
Doing up nuts and bolts to the same torque is fairly easy. Doing them to an acceptable level is also usually quite easy to achieve. Doing them to exactly the right torque is a bit more difficult but rarely critical. I've done head bolts etc too by feel and never had any problems.
Letting the ratchet fall down under it's own weight.
I wouldn't of thought that would be the correct method for a rear wheel bearing on a car with a staked wheel nut. A staked wheel nut would indicate to me that it had a preloaded taper/roller/ball bearing, and they generally get tightened far more than that.
Conventional taper roller bearings, would get tightened in a way similar to what you've said, but on vehicles, they should be adjusted until the endfloat/play is within tolerances, and the adjusting nut is usually castelated, and locked using a split pin.
Having never worked on a 323, I can't say what is fitted, but how tight was the nut to come of? If it required alot of force, then it's a preloaded bearing. If it didn't take much force, it's a conventional taper bearing.
we had this discussion about this vehicle a few months back, it does appear that there ARE vehicles using an adjustable bearing and a staked nut (daft as that is)
In an old C&CC, Dave Walker said how he was once on a tour of a torque wrench factory with a load of journos, and was asked to have a go at tightening bolts attached to a strain gauge. He got it better than the torque wrench every time. When you think why a bolt's torque is specified (to stretch the bolt a little, but not beyond it's elastic limit), you can see why...
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