Rear wheel spacers?

Keith1069 · Oct 23, 2006

Doing wheel alignment & increasing it's offset in the swingarm on my 750 I just noticed an extra spacer on the parts list which I don't have. It's the narrow item called "speedo gearbox spacer". Since it looks like it has a shoulder at the gearbox end is this item intended to centre the gearbox on the axle? I only have the long spacer (1.3")between swingarm end and speedo gearbox.
As it is the existing spacer and gearbox is a very tight fit in the swingarm so without opening up the fork ends I don't see how the extra spacer would fit. Any thoughts? What's on your rear axles? Thanks.

Ron L · Oct 23, 2006

Keith,
The spacer is probably inside your speedo drive. Check this carefully, as they become slightly crushed and allow your speedo to rub your aluminum wheel disc and can destroy the disc and speedo drive. If on re-assembly the drive rubs against the disc, replace the spacer immediately. In fact, if there is any doubt while it's apart, replace it now.

This spacer presses into the drive from the outside of the speedo drive.

hewhoistoolazytologin · Oct 23, 2006

Can someone post a scan of the parts list blowup? My gearbox has rubbed on and off for years and naturally the aluminum plate is quite ruined...I don't think I know what part you are refering to....Thanks!

L.A.B. · Oct 23, 2006

hewhoistoolazytologin said:
Can someone post a scan of the parts list blowup?

1971-75 parts lists are shown on the BSA Regal website and I would think Keith1069 is referring to part NM13270 (71-74) item 34: http://www.bsa-regal.co.uk/norton/parts ... 16&Part=34

http://www.bsa-regal.co.uk/norton/parts-list.php

hewhoistoolazytologin · Oct 23, 2006

Thanks...high hat form...... Fits outside the gearbox, according to the drawing. Whatever... my aluminum plate is done et up...the gearbox used to simply get bent/sucked, in, towards the plate, and eventually make contact. Had to take the gearbox off and flatten it in a vise, several times. It was sort of dished out and much too thick, so everything rubbed. Will check it out....maybe this is the reason....

tpeever · Oct 23, 2006

You need part number NM13270. Looks kinda like a top hat. Make sure you have one, cause if you don't, your speedo gearbox will be toast in very short order. Took me a ruined new gearbox to figure out that the previous owner of my bike had omitted this spacer which allowed the adjacent spacer to crush it. Most of the speedo gearbox spacer fits inside your speedo drive so that is why you may not see it.

Keith1069 · Oct 24, 2006

All
Again my bitsa throws up a surprise! Have just looked at the spacer and speedo box assy in case I missed it and NM13270 is definitely not in place. There is no current space for it so the S/A ends will have to be spread a little.
I have nearly 18,000 miles since '98 without it and the PO had the bike from '85 but I have a bill to show he replaced the drive in '97!
There are marks on the hub cover disc (replaced 3 yrs ago), not bad but scuffed a bit and there are signs of rubbing on the speedo drive steel felt retainer for around half the dia. I have heard a light scraping turning the wheel over during chain lubing which explains that and I guess I'm lucky there is no serious interference.

Two more questions:
1. Before I go and replace the drive which is working fine there is a .980
dia x .020 deep recess on the outside of the drive, Is that for the
NM13270 spacer?
2. On the inside of the drive in that same area there is a .125" wide
groove with an 040" wide lip that looks like it was intended to or has
engaged in the inner diameter of the bearing spacer. It's not wide
enough to have been "machined" by the spacer after say a seized
wheel bearing. Is that normal?

I ask in case I have some aftermarket drive fitted that other than the ratio is not as it should be. Part no is BG5330/171 - RATIO 15/12 .

Thanks for all the help on such a small thing.

tpeever · Oct 24, 2006

Keith1069 said:
All
Again my bitsa throws up a surprise! Have just looked at the spacer and speedo box assy in case I missed it and NM13270 is definitely not in place. There is no current space for it so the S/A ends will have to be spread a little.
I have nearly 18,000 miles since '98 without it and the PO had the bike from '85 but I have a bill to show he replaced the drive in '97!

Amazing that you could get that kind of mileage out of your speedo drive without the spacer!! My speedo drive was shot shortly after I acquired the bike and I thought it was just normal wear and tear. I replaced it (without the spacer 'cause I didn't know it needed one!!) and about 1000 miles later it was cooked again. The difference in our experiences may have been due to the cheaper quality of the replacement drives that are being sold now. Much lower quality than the original Smiths drives. Maybe you had the real Smiths drive which was presumably more durable??

There are marks on the hub cover disc (replaced 3 yrs ago), not bad but scuffed a bit and there are signs of rubbing on the speedo drive steel felt retainer for around half the dia. I have heard a light scraping turning the wheel over during chain lubing which explains that and I guess I'm lucky there is no serious interference.

Two more questions:
1. Before I go and replace the drive which is working fine there is a .980
dia x .020 deep recess on the outside of the drive, Is that for the
NM13270 spacer?

Yes, that is where the "brim" of the top hat goes

2. On the inside of the drive in that same area there is a .125" wide
groove with an 040" wide lip that looks like it was intended to or has
engaged in the inner diameter of the bearing spacer. It's not wide
enough to have been "machined" by the spacer after say a seized
wheel bearing. Is that normal?

Not sure about this. I'd have to check mine. I think that area butts up against the wheel bearing as you say

I ask in case I have some aftermarket drive fitted that other than the ratio is not as it should be. Part no is BG5330/171 - RATIO 15/12 .

That sounds like the correct part.

Thanks for all the help on such a small thing.

Keith1069 · Oct 26, 2006

All may be revealed. I got a top hat spacer from the nice people at BSA-Regal and it doesn't fit the hole in my speedo drive. Seems the groove I mentioned earlier locates on the bearing spacer (06-7704), centering the drive(extends thru the lockring) and the speedo spacer is not needed. See pictures http://aolpictures.aol.co.uk/galleries/piztonbroke/

The drive was an RGM item bought by the PO in '97 and described as up to '75. So they are either not all the same for pre Mk3 or RGM were doing a mod on drives intended for another machine.
All I need to do now is shim the drive away from the aluminum disc and with the groove inside the drive preventing any spacing here the only way I see is a shim between RH bearing and that bearing spacer.

Rear wheel spacers?

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