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Speedo gear wheel

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I have just received a speedo gear wheel for rigid Norton single. It threads onto a boss inside the brake drum. But, sadly, its inside diameter is 54mm  whereas the outside diameter of the boss is only 52mm!

I wonder which is wrong? That is...did they change? Will it be hopeless to look for a 52? Might I have to turn a 26tpi (or 1mm) left hand thread inside and outside a 1mm thick tube? 

Another problem brought about by weird design changes for no good reason perhaps?

Now to find some thin walled steel tube. Or a left hand thread helicoil, 51mm by 1mm?

Any ideas or sympathy much appreciated.

 

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David, some of the instruments and drive equipment around at the time were third party items, the scroll could be commom to many makes needing a bush to be made by the bike manufacturer. 

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Thanks Ashley. Makes sense. But why the boss has a smaller thread is strange.  Why on earth did someone decide to change? Just to make the job of the stores manager more complicated! I await developments.

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The 52mm on your hub I believe is standard. Therefore the new gear you've received must be for some other make. The correct Norton size is about 52mm and has 43 teeth. It has a wheel direction arrow stamped on the side. If yours is LH thread then that means you have a RH mounted brake. Norton changed from LH brake to RH brake in 1939. Cornucopia have a steel gear for the LH brake that has RH thread. However I can't see them having the RH brake gear listed on their website but it may be worth a call.(http://www.cornucopia-enterprises.de). There is a company in Queensland, here in Australia, BMH Trading, that makes the part in 3D printed plastic. They have them for both LH and RH mounted brakes. I have just bought one for my 1938 Norton, LH brake, and they are good quality. Only $20 AUD plus GST 10% and postage extra. This is the web page for the RH brake, LH thread, item that you are after: https://bmhstore.bmh.com.au/index.php?main_page=product_info&cPath=15_159&products_id=3968

BMH Trading also stock many other parts

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Update on my posting above. The new gear that I bought is also too big for the wheel hub. But only slightly. Apparently there are actually variations between years. Probably due to different suppliers batches (No CNC machining in those days). The ID of the gear I bought is 52.30 mm but the OD of the hub thread is 51.88 mm. Therefore the gear does not grip the thread. To add to the variances apparently some of the threads are plain parallel and some are tapered. Also some have a plain shoulder before the tapered thread starts. BMH may be able to 3D print a gear specially to fit the treads that I have

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Don't know if it's possible. 57 years ago, I had to replace a 33 years old worn out chainwheel. Impossible to find. Local motorcycle workshop turned down the old one, and fitted a new standard chainwheel that they turned off the centre of. Then fitted together and welded. Don't know if something similar could be done to your speedo gear wheel.

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Thanks for all these comments.  David's problem looks to be worse than mine, because my sleeve can be just thick enough to get  both external and internal threads.  I spent a ridiculous amount of time on the lathe with the attached result.

My supplier tells me he might source the correct one, but there's not much point.

The thread gets tighter as it goes on.  I can't confidently measure andytaper, but it might be very slight.  Anyway it works now.  I think I might Loctite it, but I'm concerned it might never come off.  Ordinary thread sealant should be OK, not bearing lock.

Incidentally: the threads seem to be a mixture of metric and Imperial. My wheel boss my my measurement is 52mm x 26 tpi, and the ring appears to be 55mm x 26 tpi. It measures 54mm internal diameter with my calipers.

But now I'm concerned - should it have a shoulder?  The bike is a 30's Inter - hence the right hand brake with left hand threads.

 

 

 

(and now I look at my own photo, I've put it on backwards!  The direction mark is on the other face.  Bother!)

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David, 

I've had time to measure a couple of spare front wheels I have and both measured the same for the hub and speedo drive. 

The inner drive rings measure 51.32mm and the hubs 52.18mm. Both speedo drives easily wind on to either hub. I measure the threads as 26tpi but due to the drive thickess a 1.0mm thread would also wind on

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Thanks Ian. I wonder if I might trouble you for a photo? I'm being lazy because I should take the wheel off my 16H and look in there...just to make sure the gear is in the correct offset from the drum. It's opposite hand of course and being QD is a bit different.

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Hi David,  Photos attached.

The identification on the gear is as follows:

Counterclockwise from the arrow (pointing anti clockwise)  are the following :

No of teeth: 43T and part no: R21078

2nd Photo added separately. 

Attachments
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Ian shows part number as 21078 whereas Nicholas shows as part number 21079

Anyone know what the differences mean?

Mike

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Ian's gear wheel has No of teeth: 43T and part no: R21078 for a 16H with 19" front wheel.

My Inter gear wheel has teeth 44T and part no. 21079 for a 21" front wheel.

So if David's Inter has a 21" front wheel I reckon it will need a 44T gear wheel like mine.

 

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Another complication! Thanks.  I do indeed have 21" wheel. I think the speedo can be calibrated to suit. Seems like I'd better chase that as well! Cycle speedo for the time being.

 

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