late 20’s speedo

[Martin27]

Hi everybody,

during my waiting time for the engine I’m trying to prepare as many other small stuffs as possible and started to check all the bits for the Cowey speedo. There is almost complete drive (just have to produce the holder), Bowden has a bit fluid rubber and falling apart, but almost everything is there. I was just checking the cog wheels of the drive. Usually those speedos has much bigger wheels, I have 18 teeth small and 48 big one. Front wheel is 3×20″. Is here someone who has experience with some similar equipment? Speedo is 80 mph Cowey, marked 307 on the body (all on the pictures). I have some other 50 teeth big cog wheel, it’s from another set, so there is something to experiment if this one shows completely wrong… anyway, would be great to hear some other experience if someone has similar equipment?

Thanks, best regards,

Martin

[Deleted User]

I have the same speedometer that I intend to fit to my TT Rep.
The gears are 55 (ring) and 18 (drive).
However, as I have yet to fit it, I don’t know what size wheel it was originally for.
I would also like to obtain the clips that hold the ring gear to the wheel – does anyone know where to obtain them?
Chris.

[Deleted User]

Also, does anyone have details of the drive retaining bracket and where it is actually fixed?
Chris.

[SwedScott]

Hi

I also have one of those old Coveys and the information I have is a copy of an article in the VMCC magazine years ago.
Stated in that article is: The number of teeth in the driving wheel can always be found by multiplying the distance in inches from the ground to the centre of the wheel by four and adding one to that number.
The author, Ken Shepard, had quoted from Covey’s own instructions.
I hope that this can be of some help for you.

Best regards
Leif

[Martin27]

Hi Chris and Leif,

ok, sounds perfect, so I just go to take my calculator. Hope I didn’t forget the math since the school, it’s already some time.
I created some autocad drawings to make both, drive brackets and the drive wheel holder. Standard holder of the cowey is for a bit smaller hubs, so I had to create “in between” wheel attached to the sprockets holes and into the outside ring threads to attach the cog wheel it self. Same with the drive bracket. I made it in two parts and will drill exactly by the dimension on the bike. If you are not in a hurry, I will make the pictures when I will finish the work and I could send you my drawings, you will see if you like it and if you use it as it is or if you need longer bracket.

Thanks, best regards,

Martin

[Deleted User]

Well, according to Lief’s calculations, the ring on my bike should have 49 teeth (the measurement from floor to c/l of wheel is exactly 12″).
Does the article state that the standard Cowie drive is 18 teeth?
Chris.

[SwedScott]

Hi again

Yes 18 teeth could be considered as standard. To quote this article again:
“For all standard needs, the driven wheel has 18 theeth, whether 10 pitch or 12 pitch.”
Note that there exists two pitches of theeth, of which 12 pitch has a smaller diameter. (No dimensions stated.)
They are obviously not comparable with each other.
I think that 49 theet sounds right for 12″ centre height.
I once had my Cowey serviced by an expert (of the old kind, that really where experts), he told me that they could be “fine tuned” to show exact speed. Sadly he passed away years ago, and I know nobody that can service them nowadays.
Again stating the article: “If the head works, leave it alone because the chances are that it won’t ever work again if you interfere with it. In my unfortunate experience, even professionals have got into a dreadful mess with Cowey heads.”

Good luck with your speedos!
Leif

[Deleted User]

Thanks for the info Lief.
So, now I have to swap my 55 tooth ring for a 49 tooth ring.
Does anyone know where these things can be purchased?
Chris.

[Martin27]

Well, this seems to be point. By my counting I should have 53 teeth, so I have to change mine as well. In my stock is 48 and 50 only. I will need 49 teeth in the future for my little 1923 Velocette two stroker, but in this case I should be almost Ok with one of those two. Any info about someone producing drive wheels welcome.
Thanks, best regards,
Martin

[SwedScott]

Hi again

I don’t think that some cog more or less will make any great difference. One thooth will change the drive ratio about 2%.
To put that into perspective modern speedometers are allowed a difference of showing 0% to little (to avoid speeding tickets!) to a whooping 7% too much!
Also take in account that the speedo head is old and might not show exactly right figures, and that that the wheel circumference changes when the tyre wears.
If you have a combination that’s nearly right, at hand, I would advise you to try it before going into a lengthy search for another sprocket.

Best regards
Leif

[Deleted User]

Dead right.
The police have to have accurate speedos, but for the rest of us, near enough really is good enough.
Personally, as long as the needle actually moves when riding…… 😀

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