Chronometric cable rotation

[Jim Hultman]

Hello everyone.  Just discovered this forum while doing some research on a chronometric tach for a 1957 A10 rat project I'm building out of an old chopper.  It's posted on the Britbike.com forum if you want to see it.  Anyway, it's up and running, and if it would stop raining and snowing here it's ready for the road, except for the instruments.  So here's the story:

It appears that A10 tach cables are clockwise rotation, driven off the mag gear. All four of the spare chrono tachs I have are clockwise needle rotation, but it takes counter-clockwise cable rotation to make them work.

I know that you could order chronos in any configuration you wanted, but this seems strange. One of my spares is mounted on what I thought was an A10 mount, which fit on the rat A10, but the tach is the wrong rotation. Does anyone know if the later A10's with the tach drive off the oil pump were opposite (CCW) cable rotation? That would explain why the BSA setup is wrong for the '57 I'm building.

Any help would be appreciated!

[Beezageezauk]

Hi Jim,

Welcome to our friendly forum and I hope that you enjoy becoming part of it.  I do, however, recognise your name from another forum that I frequent.

I've just contacted a friend who repairs chronometric instruments and he tells me that all A10 swinging arm model BSA Speedo's and Tacho's work in the same direction (anti clockwise) and a reverse direction variable speed drill is needed to test them out.  Are you sure that the tacho in question is for that particular model??

Let's hope that the information I'm relaying is correct!!  If not, I'm sure somebody on the forum will correct me.

Beezageezauk.

[dpaddock]

Perhaps I'll be corrected but, as far as I know, the cable has to rotate in the same direction as the needle.

David

[Jim Hultman]

Perhaps I'll be corrected but, as far as I know, the cable has to rotate in the same direction as the needle.

Yeah, that' s what I thought too, but evidently it's only true with magnetic instruments.  I was just goofing around when I reversed the drill on these, and just about dropped it when they started to work!  But they clearly do work with the cable rotation opposite the needle rotation.

I'm told it isn't hard to reverse them, but you really have to know how, and I don't! 

[Jim Hultman]

Hi Jim,

Welcome to our friendly forum and I hope that you enjoy becoming part of it.  I do, however, recognise your name from another forum that I frequent.

Beezageezauk.

Uh oh.  Hope I didn't say anything dumb on the other forum!    Let me guess....Britbike.com?  Are you Beezagunk or something like that?

[trevinoz]

The tacho fitted to the post 1959 Rocket was driven from the oil pump and rotated in the opposite direction to the one which was driven from the magy.
The ratio of the oil pump driven type is 3:1 which should be marked on the face.
           Trev.

[wilko]

Chrono's always spin clockwise looking at the face, but looking from behind with your drill attached it is anti!! I've pulled dozens apart. It's the drives on different bikes that make the difference.Depends on whether it's driven from maggy's or camshafts.

[MikeN]

A few years ago Dave Woods the speedo reconditioner used to pay me £5 a go to convert chronometric speedos to reverse direction. He would give me an ice-cream tub full of the almost bare die-cast main chassis and I would remove the small pinion and spindle from where the cable enters. On the Bridgeport I would  mill the casting down locally to  (i think) 3/16" thick . Which allowed the small gear to either move into or out of mesh. I cant remember which way,now. It took me about 1 1/2 hours to do 20 units. That is, remove the gear in the chassis, clamp it in the vice and mill the chassis ,de-burr and re-assemble .
 So I can say definately that the cable direction does not have to rotate the same direction as the needle,although it can if you wish it to. Its all down to what the customer requires and how the builder assembles it. Any chronometric instrument can be assembled to become anyting you wish.A "D" shaped Bantam clockwise speedo can become a 5" Vincent anti-clock rev counter (and frequently do I believe).
The internals are all made from standard  parts but are easily adptable and are calibrated by adding and subtracting the specially shaped weights to the oscilating flywheel part(I dont know the correct name) of the mechanism, when its on the calibration rig.
Mike

[Jim Hultman]

The tacho fitted to the post 1959 Rocket was driven from the oil pump and rotated in the opposite direction to the one which was driven from the magy.

Bingo.  That's the explanation I needed.  I have found out that an RC83 tach is the CW version for the early mag drive bikes, and I do have one of those.  It was stuck, so I had to get it freed up before I could prove the theory, but it does work now and in the proper direction for this bike.

What had me confused was that the instruments I was trying to use came to me with a basket A10, so I just assumed they would be correct.  But the bike they came with (which I built years ago) was a '62, with the tach drive off the oil pump.  I ended up building that one with a nacelle, so I didn't use this tach.

Now it makes sense!!

Appreciate the help!!

[dpaddock]

Thanks to all for a very enlightening discussion.

David

[Beezageezauk]

Enlightening it certainly is and makes me proud to be associated with a forum with so many knowledgeable members.  I often wonder how we managed to maintain our bikes before the advent of the internet!!

Oh Jim, I also use the name beezageezauk on BritBike.com

Beezageezauk.