Wanted CP speedo drive gear

[Paul Gasson]

I have finished my 1950 NH project bike and am very pleased after my first 150 miles of running in. There is one small piece that I would like to find to complete the bike, a speedo drive gear. The part I strongly think I am searching for is 3151-50, made after the correction of the gearing to suit a Chronometric speedo, it should have 13 teeth and a shallow groove at one end as shown in the photos I found when searching through the forum (right side item where two parts are in photo). Also as described in part of the factory bulletin below.

Details of part numbers and applications has come from Roger Gwynn and I have spoken to Geoff Brown who advises he cannot supply this item, only the earlier PA drive ratio, which would ruin my perfect correct specification layshaft if used and give incorrect speed readings. I have followed leads as far as Australia already but come to a dead end so if anyone can help with a decent part, it would be appreciated. I will pay a good price and cover all shipping costs. Please, if you have any CP spares or even parts you might think are for a BA gearbox, would you have a look through them when you have a minute. It would be the perfect Christmas present!

Thank you

[JohnnyBeckett]

hi have been onto Geoff Brown the clubs gearbox spares and see if has one or knows where to get one , or he may be able to get you one made made, he is very good and helpful

[Paul Gasson]

Thanks Johnny, I tried Geoff and he only has the speedo gear for a CP with PA setup, I asked about the gear I need and he said the manufacturer used cannot make it, presumably he does not have the correct cutter. If I understood correctly, it means it’s not possible to supply parts for a CP box used with a Chronometric speedo head and achieve the correct flex speed to give accurate speedo readings. That’s why I am appealing for help, I found photos in the forum so I know the part exists, just need to find someone who is prepared to sell one. Will keep using the cycle computer until something turns up.

[JohnnyBeckett]

hi Paul i would keep looking on Ebay under Ariel parts you may find someone who has got a gearbox for spares i got a GB complete box off Ebay this time last year for £30 pounds plus £10 post and packing

[nevhunter]

I'm a bit surprised you can't get one made. In principle it's only a multi start very coarse thread. It could be made using hard bronze (Not brass). Dissimilar metals work better in worm or skew gears. Nev

[Paul Gasson]

Johnny, I keep checking eBay but have only seen one speedo gear offered, it was the wrong one! I have seen a few gearboxes of the correct type and asked sellers if a gear is in place, generally they have not been prepared to check, despite it being fairly simple to see if one is present. I’ll keep looking there.

Nev, I’m not sure it would be so easy to make one, presumably it would involve a milling machine, dividing head and a cutter with the correct form. I suspect all of the speedo gears are approximately the same diameter but with a variation in the number of teeth, I guess the shape of each tooth will be different. That’s well beyond my abilities. There are a couple of businesses in UK who make one off gears but they would want my gearbox, in pieces, to get measurement details and having just got the bike on the road, I’m not ready to take it apart again already. When I bought the bike some years ago, I had no idea this small part would become the most difficult to locate and wish I had started looking earlier. Especially as I got the Chronometric speedo serviced in anticipation!