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MG Midget and Sprite Technical - Big discs and wheel bearings

After nearly two years set under my bench, I have finally got round to fitting some oversized discs and 4 pot calipers to my Mk IV Sprite. (First car track day next month)

The kit includes new hubs with taper roller bearings. In the fitting instructions there are two suggested options with regard to bearing adjustment.
1) Uses a spacer and shims between the bearings a bit like an MGB.
2) Suggests not using the spacer etc and just using the spindle nut to adjust the play/preload and then locating it with the split pin.

My research on the BBS archive suggests that with shims I should aim for .001-.004" play at the hub. I've done that, but once I've refitted the road wheel, it feels like there is quite a large amount of movement at the rim (6 & 12 O'clock)
Incidentally, when I've shimmed BMW motorcycle wheel bearings there is supposed to be preload, and there is an inch-pounds measurement of torque to aim for with a special tool. (I actually use a spring balance, a spool of known diameter and a piece of string!)

Setting aside the debate about using shims or not, heat transfer and differential expansion as well as the possible merits of the added strength of a shimmed spindle, can anybody give me an estimate of the amount of movement there should be at the wheel rim when the hubs are adjusted correctly?

I've looked at SKF and Timken data sheets and they both come up with free play figures in the hub in the range .001"- .010" That amount of play feels sort of "wrong", but then I'm more used to two wheels line astern and without any wobble at all.

Thank, Mark
M Crossley

Mark,
I am no expert in the field but I have fitted press-in (from the back) stub axles (and taper bearings) to my TC race car and because of the press-in part, I MUST use the spacer option as the nut also holds the stub in place. If your stubs are held in place by other means, you have both options but I would favour spacer and shims. It is more of a pain to set up but I believe it is the stronger, more reliable option. Whichever way you go, I suggest you cross drill the split-pin hole as that halves the size of tightening/adjusting increments.

As I said, I am not an expert in the field but I always aim to get zero preload (but no play) to very slight play at the wheel rim. I would think barely discernable play is perfect. Maybe I am a cowboy but I don't mind rubbing the spacer or nut on a file or emery to get things exactly how I want them. I agree that .010" seems way too much .... I guess that would result in about a half inch at the rim!

Good luck with the project and the track day!

Bob Schapel
R L Schapel

Hi Bob,

I am tending towards using the spacers, although I am using standard uprights so i don't have to worry about the spindles working loose.

The zero play without preload feels like a good compromise. Its what my latest attempt has aimed at. Your description of 'barely discernible' play is what I've ended up with at the rim.

My current plan is to bed in the brakes, get them hot and check for binding.

Like you I got close with shims and then used 320 grit on the spacers to sneak up on the no play target.
The emery tip is an accepted technique when shimming BMW Airhead wheels!

Mark
M Crossley

lol
Mark
Don't listen to Bob, labeling himself as a cowboy---
We all know better than that--he has lots of experience and knows what works-
I agree with zero play and maybe a tiddle of preload to help make things stay in place under load
The spacers, in my opinion are a must for spirited driving, with the nut up dead tight----This has the effect of making the stub axle o.d. increase to that of the o.d. of the spacer which in turn reduces flex of the outer of the stubaxle-----all good
Enjoy your track outing

willy
William Revit

When you say you set the end float on the front hubs,how did measure it, did you use a clock, also what is most important is, that all the measurements are done dry (clean with no grease) for a B it should be between 0.002" TO 0.004", and the hub nut should be tightened between 40lb/ft to 70lb/ft, then when you have set the correct endfloat, you pack it with grease and fit the hub seal, if you did not do it like that, then you have done it wrong, A.T
andy tilney

Andy,
Yes I used a dti gauge. Magnetic base on the disc, pin on the end of the spindle. Bearings temporarily oiled with 3 in 1.
I'm not unfamiliar with shimming taper rollers, just not on a car. So I have no real 'feel' for what's good or bad. I looked at MGB for a clue, although it isn't exactly the same. I started off with .003" end float, but that gave what felt like a lot of movement when I trial fitted the wheel. Perhaps that's normal, but that's the bit I'm unsure about.

I understand that at least part of the reason for the end float on a B is to allow for differential expansion, when the brakes are used.
These are vented discs that are mounted in the modern way on the front of the hub, so I'm hoping that they will dissipate more heat more quickly.

If you shim a B wheel to .003", how much movement do you get at the wheel rim? I started checking to see if there was wear in the suspension because it felt quite wobbly. Perhaps "They're all like that, sir" !!!

Ta, Mark


M Crossley

Mark. as the end float is measured on the hub, and as you have set it to 0.003", the movement you feel on the wheel is not important, what is important is that you can feel some play on the wheel, then you know the bearings are not set to tight, as you are fully aware by holding the wheel at 12 and 6 o'clock you have a bigger lever, these bearings must have between 0.002" and 0.004" end float, that is what is important not wheel movement, you will do more damage to these bearing by having them to tight than you will by having some end float, don't confuse these bearings with other types and other applications, this is how these are,A.T
andy tilney

I have found on the B that greased bearings at 2 thou dry doesn't have any significant play at the wheel, at 4 thou there is play. That gives a useful envelope for setting the bearings up.
Paul Walbran

This thread was discussed between 16/06/2016 and 17/06/2016

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