Front hub runout

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Aiden

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Hello,
I have an issue with the front brake rotor/hub on my 74 mkII. I sent the wheel to be laced at buchanans and mounted an Avon roadrider, replaced the rotor due to pitting of the original. I mounted it up and have severe wobble of the rotor that I have determined to be the result of 0.003” runout of the hub where the rotor mounts, which equates to 0.014” at the edge of the rotor.
I can’t get a machine shop to touch it with a 10 foot pole locally, so I am wondering if anyone has any suggestions. Would it be possible to machine the hub without dismantling everything? Does anyone have recommendations for a shop in the west coast US? I have read about tapered rotor shims, does something like this exist for a Norton?
Thanks for the help,
Aiden
 
I can't think why a fresh rim would introduce this problem in your hub, unless it was dropped or damaged? If not, maybe the issue was already there and removing the rotor, means you have put it back on in a different position. Try moving the rotor round, one hole at a time?
 
I would have the brake disc checked for warping in a lathe, as it's the likely culprit. Maybe it can be trued if not too worn. Recommended minimum thickness is 0.25" according to this thread:

www.accessnorton.com

Minimum Disc thickness

I am still having trouble with my front brake and have started looking at another angle. I know I have a high spot on the disc and have thought about having it ground flat again. Can someone tell me the minimum thickness allowed for the front disck. I can't seem to find that informatin in my...
www.accessnorton.com www.accessnorton.com

- Knut
 
Did you reinstall the old rotor to see if it also exhibits the wobble? Regression testing.

Very difficult to bend a hub. Not so difficult to bend a rotor. Might have happened when the tire was mounted.
 
Thanks for the replies. I was initially suspicious of the new rotor as well, but before I called them up, I wanted to check the hub, as there was a note that came with the rotor saying it was guaranteed to 0.001” true, and to have the hub trued by a precision machine shop if runout exceeded that. The runout of the hub was measured using a dial indicator that was clamped to the axle and was very repeatable. I will try the old disc and changing the position of the new one.
Also, the rotor was not installed until after the wheel was laced and the tire mounted.
 
Have you ridden the bike to see if the front brake chatters when applied?

Does the rotor hit the pads when spinning the wheel?

I'm also curious if 0.014 is visibly noticeable when spinning the rotor. It's about the thickness of paper. Is that what caught your eye? Or did you whip out the dial gage right after mounting the wheel?
 
Schwany,
The bike was torn down to the frame and I have never ridden it so can’t answer that. Yes, visible wobble was what made me start investigating, it actually touched the steel plate on the back side of the caliper with no pads yet installed.
 
If it was touching the caliper without pads in it, you'd feel it when applying the brakes. Did you check the spokes for equal tension? Is the hub out on both sides equally?

I can't wrap my head around how the hub would show wobble once on the axle and everything is tightened up. BTW I don't own a disc brake Norton, but have owned a lot of disc brake bikes, so maybe I should just STFU and let the experts get you on track.
 
No, I appreciate the input. To be clear, the wobble is not visible on the hub, but only once the rotor is mounted and that runout is amplified by the larger diameter of the rotor
 
The disc side spokes will be lower tension than the non disc side, a consequence of the design. I would be looking to check the hub bearings are fully seated first.
 
That’s an interesting thought. I believe I seated them fully, but can check again. If that were the case though, wouldn’t I see wobble at the level of the tire though? The wheel spins nice and true, at least visibly
 
I am assuming that the hub itself is the constant and all of the other parts have iterated? Is that a true statement?

If the bearings were changed, where did you get your bearings?
 
Rim and hub are original; spokes, rotor and bearings are new. Bearings were from classic British spares and did not come in a package indicating their origin
 
The spokes won't affect the run of the hub. With the wheel rim running true, it suggests it's the hub to rotor fitment or the hub itself, not the bearings, unless exactly the same issue with the bearings was also happening when the wheel was being built. My disc/rotor is pretty much central in the calliper, so I don't think that small amount of run out should result in it hitting the calliper?
 
It does seem like to be visible and to rub the caliper it would have to be more runout at the rotor than that. I measured the hub numerous times, I am less confident in the rotor number, will recheck that.
 
Aiden said:
Yes, visible wobble was what made me start investigating, it actually touched the steel plate on the back side of the caliper with no pads yet installed.
Click to expand...


Disc scraper (065143)? As there wouldn't normally be any other "steel plate"?
www.rgmnorton.co.uk

STAINLESS STEEL BRAKE DISC SCRAPER

INTRODUCED BY NORTON IN 1973 AND USED ON THE PRE MK3 850 FROM ENGINE NUMBER 307311, BASICALLY 850 MK2 AND MK2A MACHINES HAD THIS SCRAPER FITTED ON THE LEADING
www.rgmnorton.co.uk

If so, then best removed it in my opinion.

The only other "steel" item would be the inner brake piston which doesn't look much like a plate.

andover-norton.co.uk

Motorcycle parts and spares for Norton motorbikes - Genuine Andover Norton Spare Parts - Andover Norton Motorcycles Parts - Original Andover Norton Parts

Motorcycle parts and spares for Andover Norton motorbikes: Andover Norton manufactures and supplies all Genuine Factory Spare Parts for Norton motorcycles built before 2002.
andover-norton.co.uk
 
Yes, sorry I didn’t know the name.
Rechecked rotor runout at 0.015”. Put the old rotor on and get 0.011
 
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