How much disc run-out before it's a nuisance?

[dikko]

How long is a piece of string maybe....


Rebuilding my little whizzer I have found some run-out on the bearing carrier what is the limit before I throw it away?

Firstly it is the common-or-garden Triumph Herald/Spitfire etc front used on thousands of Formula Fords and plenty of race cars. The great lump you bolt the disc to and your wheel....

I have found that with new stub axle and bearings I have TEN thou of run-out at the edge of the hub/bearing carrier. The unit seems to have been built like it (Factory tolerance I guess) and it's rather involved to get it re-aligned - I'm informed. Cheaper to buy another.

The ten thou involved will progress out to 20 at the disc edge & caliper (I've not measured it) and will give me knock-back, knock-off(?) effecting braking delay.
Will it be too much? How much do other people stand for before throwing?

[Dave Brand]

That's a lot of runout! From memory, most manufacturers specify a maximum disc runout of .002" or so. Rectifying the hub would, as you say, be a difficult operation as to locate it accurately on the lathe you'd need to replicate the production tooling & even then you'd then run the risk of having to remove so much metal that the position of the disc locating face would be outside design limits.

An option you might consider is having the discs machined on the vehicle, which will give you the absolute minimum runout; however, with the runout you've got at the hub it may well be impossible to true up the discs without going below minimum thickness.

[Robyn Slater]

I had the same problem with my alloy hubs. I thought it was distortion in the disc.

They can be machined on a lathe;without removing too much material.
If you know how.

[historic racer]

Originally Posted by Robyn Slater

I had the same problem with my alloy hubs. I thought it was distortion in the disc.

They can be machined on a lathe;without removing too much material.
If you know how.

Thought the purpose of this forum was to assist people not give them smug answers

[GORDON STREETER]

Originally Posted by Robyn Slater

I had the same problem with my alloy hubs. I thought it was distortion in the disc.

As an aside Robyn I have had two of those alloy hubs break up on my Anglia and fitted iron ones !
Also they weren't rubbish ones !

[Robyn Slater]

Originally Posted by historic racer

Thought the purpose of this forum was to assist people not give them smug answers

What was the question??

[dikko]

Thanks for that Mr B I now know it is not acceptable (without seeing how it is on the track.....!) and will do something about it. Two forward..three back....

[Dave Brand]

A further thought on this - with that much runout on the hub face the wheel's going to be running well out of true!

[Dave Brand]

Originally Posted by Dave Brand

A further thought on this - with that much runout on the hub face the wheel's going to be running well out of true!

Too late to edit, so:

. . . or maybe not. Reading the original post again, I see it's an older-type hub, so the disc probably mounts on the back face of the hub rather than the front face as I'd assumed. If so, it's not such a difficult machining job as the front face can be used as a datum. Depends if you can get it done for free!

[dikko]

Yes, goes on rear of Hub and No, I don't have that kind of machinery to hand...it is all quite odd, 5 thou out here minus 5 there 10 there. New it is then...