Frankenstein tacho set up.

[UncleD]

Morning all,
Can anyone identify the attached Smiths tacho gearbox?  It is marked BG 1304/13A.  I can't find any information on its direction, ratio or what models it may have been fitted to.

It is currently on my 58 Super Rocket.  The tacho on the bike is a modified Chronometric speedo and as I understand it is a clockwise instrument.

The tacho gearbox is driven through the magneto (K2F) by a Frankenstein nut on the ATD. 

The tacho has never worked as I believe the gearbox is not reversing (the tacho works when I put a drill directly on the cable in a clockwise direction).  There was a reversing cog floating around the tacho housing when I opened it so I am starting to think this is where the PO tried to reverse the direction to accommodate the incorrect gearbox.

I understand the correct gearbox should be a 65-9164 (Smiths 1508/05) which is a 1:1 reversing.

So what on earth have I got?

If I found the correct gearbox, would it connect with the magneto?  I have heard talk that an ATD cannot accommodate a tacho drive...is that correct? 

Does this expalin the bodgy connection (Frankenstein nut!) between gearbox and magneto? 

Would the drag of the tacho cable affect the bob weights and therefore engine timing? The bike starts and runs reasonably well.

Thanks to all.

PS I will try to post some photos ...having a bit of trouble even when reducing their size...

[UncleD]

Front

[UncleD]

Rear

[UncleD]

Frankenstein nut!

[kiwipom]

Hi, have no idea except to say that some car tacko drives we’re converted to fit, a mate had a Triumph 2000 one on his B33 racer, cheers

[KiwiGF]

Old Massey Ferguson (tractor) tacho drives are cheap and sometimes used as a custom solution.....see https://www.ebay.com/p/Tachometer-Drive-535126M93-for-Massey-Ferguson/1719538897

[UncleD]

Righto, so it seems that I have the following;

- A 1958 Super Rocket that was designed to have a tacho driven off the magneto.
- A Chronometric speedo converted to a tacho (clockwise 2:1)
- A K2F magneto (anticlockwise) with ATD*.
- A home-made slotted bolt in the ATD which drives the tacho cable.
- A tractor tacho gearbox that is non reversing and therefore incompatible with the clockwise tacho.

* I have read that ATD and magneto driven tacho are incompatible and so suspect this magneto is probably from a later model or has been retro-fitted with ATD...and that the PO has bodged the ATD bolt so that it accepts the tacho drive.

I would think that reverting to manual advance/retard to accept tacho drive (ala pre 1960)...or changing to an oil pump driven tacho (post 1960) are both expensive, difficult and/or undesirable options.

I would like to keep the tacho!

Is there any way an ATD can accept the correct (1:1 reversing) tacho gearbox?

I am hoping for a miracle cure.

[Greybeard]

Electronic tacho?

[chaterlea25]

Hi D,
Firstly I would check the calibration of the rev counter, a drill or lathe with a known speed should be good enough to see what the ratio is
 The mag could be converted to manual advance and a fixed pinion bought.
Then source the correct drive box
All options require capital injection

John

[Black Sheep]

Would driving the tacho through the auto advance mechanism interfere with the ignition timing? I rather suspect it would. There's no cheap solution. You need to convert the magneto to manual (not too difficult) and buy a correct tacho gearbox. Not so very long until Santa comes round again...

[Triton Thrasher]

Would driving the tacho through the auto advance mechanism interfere with the ignition timing?

Yes.

[UncleD]

Ok...process of eliminating least desirable options.

Converting to oil pump driven tacho will be expensive and moves the 58 further away from stock.
Although the cheapest option, losing the tacho and tacho drive on the timing cover will change the look of the bike too much and I can't find convincing reasons to do this in order to retain the ATD.

Soooo...I'm leaning towards converting back to manual A/R to retain the mag driven tacho. 

Given my technical skills and the history of bodges already discovered, I will inquire into the cost of professional conversion and refurbishment of the mag at the same time. 

I understand that in addition to the mag internals, this will require a different end to the mag to accommodate the A/R cable, cable and lever.  It will also need a different (non fibre) pinion.  Depending on the end cap chosen on the mag, I may lose my current handlebar mounted cut off switch.  I will also need to source an appropriate tacho gearbox.  Is there anything else that I need to consider in making this changeover?

With manual A/R I am expecting to have to work out the sweet retard spot at start up, and perhaps when starting off at traffic lights (given that I rarely have a pillion and there are no hills in the Northern Territory I don't anticipate other situations where I will be fiddling with A/R).

I am happy for anyone to probe my logic...whichever way I go there will be cost and complications so the first decision in the sequence needs to be the best one, because there will be no turning back.

PS: any recommendations on Australian mag specialists?  Anyone dealt with Antique Auto Electrics in Bendigo?

[kiwipom]

Hi, do you have a manual magneto as I am not shore that  the a.t.d mag can be converted so if not the expense of another mag would be involved, cheers

[Tomcat]

PS: any recommendations on Australian mag specialists?  Anyone dealt with Antique Auto Electrics in Bendigo?

Peter Scott in Seven Hills NSW reconditioned the magneto on my A7 14 years ago and the same on the A10 2 years ago and both are faultless.
I would not recommend TT Enterprises in NSW.
HTH Cheers TC

[muskrat]

Peter did mine 30 years ago. Not been on the A7 for 25 years but still gives a good shock when spun by hand.
Just around the corner from Peter is http://www.zochys-magnetos.com/
Not dealt with but have good reports from others.
Or set the tacho to 1200rpm and not connect it. Start the bike show people how steady the tacho is then put your arm over it when you rev it. 
Cheers