The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Frame => Topic started by: UncleD on 29.12. 2018 00:32
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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...
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Front
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Rear
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Frankenstein nut!
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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
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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
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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.
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Electronic tacho?
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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 *eek*
John
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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...
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Would driving the tacho through the auto advance mechanism interfere with the ignition timing?
Yes.
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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?
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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
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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
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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. *bash*
Cheers
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I had my Mag done at Zochys... Aus Post managed to returned it broken, I contacted the owner & he replaced the broken part.. free of charge.. & it hasn't skipped a beat in 4 years.. *wink2*
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The mag can be converted OK, but there is a little bit to do.
Change of end-housing at the cb end as mentioned;
change of camring for one with notches in it to allow for movement and to fit the operating plunger (you could mod the ring that's there, but probably need to polish / relieve the outside of the ring to get it to be a sliding fit not a tight one);
extract and refit bearing outer race into the manual housing;
buy AR cable and gubbins;
maybe have to find different cb end cover depending on type of housing sourced. The only sort that makes remote kill/ stop button difficult is the end with the alloy dome fitting with metal button - other types used on twins have the facility for a wire to go to 'bars. Even one of them can be converted to use a brush and spring in an insulated sleeve, with a wire off.
This can all be done with the mag in situ on the bike. But if it's coming off for a general checkover, then all well and good and a complete new bearing could be fitted at the same time probably, with the armature out.
With the manual set-up on an A, you might need to change the front HT pick-up if it fouls the AR cable entry. The usual 45°-angled pick-up (if it's got one of them) isn't deeply-enough cranked for clearance - a vertical one will go on, just, and there are cranked ones available, though their quality isn't always too special.
Then you need your fixed gear - there were some neat alloy ones out there at one point (SRM I think), probably still are - and a non-Frankenstein nut for the tacho drive.
The most expensive thing there would be a replacement manual camring if you went for new, so I'd mod the old one if it's any good. Dremel or similar fine grinder and steady hands or bench fixture to enlarge the notch that limits movement, and then to make the V slot for the cable plunger. They do have to be in the right spots, or it's TROUBLE. Elongate the notch that's already there to about 10-11mm long to provide retard only - ie to allow the ring to rotate clockwise from where it currently sits. Then set the ring to the middle position of its new-found movement and mark it at mid-point of the range of movement of the plunger. Cut V slot. That way, the plunger won't slip out of engagement at full A or full R. The eccentric pin can then be used for fine tuning if necessary - to get the points to open just after the relevant flip point of the armature at full advance.
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Bill, another greatly informative piece!
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For the Aussies, Zochy is now relocated to Harrington, N.S.W.
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I had my Mag done at Zochys... Aus Post managed to returned it broken, I contacted the owner & he replaced the broken part.. free of charge.. & it hasn't skipped a beat in 4 years.. *wink2*
Yep, Peter Scott said to me,'Package the magneto up with ample padding so Aus Post can kick it around a bit!'
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Well I took the first step on the quest last night.
My most immediate concern was the effect the resistance from the tacho drive was having on the engine as it was was bodged up to the ATD. As it was intended for a tractor and was not reversing, it had the least inherent value of all the components and so had to go. I could not extract the gears (to only leave the casing in place) so got out the Dremmel and cut off the drive paddle (yes, I have fallen to the bodgy dark-side). She now sits in place (along with the tacho and cable) and looks the part but is not interfering with the timing. Not the ideal situation as I do like things to work properly, but a good step along the way .
I can now search up the correct tacho drive (65-9164) and modify the mag in my own time which are going to be significantly challenging and costly steps.
Thanks to all for your feedback, thoughts and suggestions.
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G'day UncleD.
I have a spare alloy pinion and tacho drive nut if you want to borrow/use & replace, if you want to go further.
Cheers
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Put 40 miles on her yesterday with the ATD uninhibited by the tacho drive. Chopped the plugs when I got to the gate and was pleased to find both plugs burning evenly if perhaps a fraction lean. Previously the right plug was noticeably sootier than the left. I have a gasket and jet set for the carb waiting to go in so will lift the needle a slot also.
I have a noise /vibration between 60-65mph that I need to locate and then attend to the point gaps /timing in the current mag so have plenty to do before considering changing to a manual mag to accept tacho drive.
I also have a parcel waiting for me at the post office which I suspect are SRM sumps for the A10 & A65...and the Harley is on the stand waiting for new points and advance retard mechanism which should be here Friday.
...and I have a week left of holidays!
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UncleD,
I went back to see a picture of your bike. OK, it's not a bitsa and apparently came from the factory with a tach. I understand your wanting to stay close to original, that said, there were lots of original models that left the factory without tachs. I do not have a tach on my '55 swingarm. I never feel like I need one to know when to shift. I have no intention of challenging some published redline, and think I can tell when I'm revved as high as I want on the engine I toiled to buirld. I think my engine runs quite well on its ATD timing and would not want to lose it. So, even though Groily has provided fantastic step-by-step instructions, my advice as the owner of a bitsa Road Rocket and a '57 A7 (also without tach) would be to remove the non-functioning tach and drive from your bike. Plug the tach hole in the timing cover using the prescribed cover and wired-safe bolts. Replace the instrument bracket for a single device. Keep the ATD and don't modify your magneto for manual advance. OK, I hear you. You want the tach. So, you could do as I advise and leave it that way until real serious engine work is necessary, and we all know that's in our futures. In my case, being cheap, scheduling of the work would include waiting for all the parts to come along at the right price.
Prepared for admonishment as necessary.
Richard L.
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I'm pretty much of the same mind Richard.
I have a 67 Thunderbolt (no tacho) but really like the look of both instruments on the S/R...however don't need it at all for riding so at this stage I'm happy with it being there just for looks.
Maybe in time I will convert the mag etc so that the tacho is operable however I am not made of money and my priority is to have the bike running and riding at its best so there are a few other jobs that will come first (like rear brakes that actually work)!
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I think you're very wise Uncle.
I've got tachos on one or two machines, and apart from looking very pretty, they're not that useful really in ordinary road use. How often (if we're not called Musky!) do we go to 6K+ rpm? Does an A go that far (twice!) anyway? - I've never tried on my low compression engine with no extra goodies like a better oil pump, end-feed crank, etc.
I only ever want to land somewhere in the middle of the torque curve on upward changes - and that doesn't need full revs on a cooking motor.
The chronometric tachos - I have one on a Notrun 650SS - are slow to react to fast throttle movements anyway I find (compared to the magnetic jobs I've got elsewhere). And accuracy isn't guaranteed either. They do look good, I so agree, but the drive boxes cost an arm and a leg . . .
The only machine I thrash to within an inch of its life hasn't even got a tachometer (and it would scare me if I saw how often it hit 7000 in second). But that's an AMC twin (I know, I know, there are those that hate them - but I love them after 43 years with one or more in the shed). Knocks the spots off yer average A . . . until, that is, you come to a . . . bend.
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Yep, just hold it flat till it stops gaining speed then change up a gear *eek* *bash*
Cheers