Plunger tachometer drive

[Steveba10]

Hi, I hope this is the right section.
I’m thinking about constructing a tachometer drive for my A10 ‘57 plunger.
I’ve looked at threads and web-sites and it all seems a bit expensive so I’m looking to see if I can do it a bit more economically.
Going back to basics I think a drive off the magneto would be best as I’m sure I can modify a magneto nut to provide the drive better than I could modify a oil pump worm. Also less chance of oil leakage. I also like the look of the angle drive on the casing.
I have two angle drives from jaguar cars, both 1:1 ratio that I’m sure I can mount onto a timing gear casing The A10 mag runs anti clockwise looking at into the driven end, the angle drives would not convert this so the drive looking into the back of a tachometer would have to be clockwise. This may be a problem as the only reproduction smiths tachometer I have seen are described as anti-clockwise and I think 4:1 ratio where I would need 2:1.
Anyone any thoughts?

[RDfella]

I believe small reduction gearboxes are available especially for this problem. Frost (who specialise in restoration equipment) may be able to advise. Or Denis Welch motorsport are very helpful guys.

[morris]

Have a look here;
https://www.a7a10.net/forum/index.php?topic=15531.0
The bottom post contains a link to a website with all kinds of gearboxes for speedo/tacho’s.

[muskrat]

G'day Steve.
Is the mag auto or manual advance? If manual all good. If auto the drag of the tacho may hinder the auto advance from working.
Cheers

[Steveba10]

Hi, thank you for your replies.
I’ve got a little further towards a cheap solution to emulate a gold star style tachometer for my plunger.
Initially I thought I would need a 2:1 reversing gearbox in the cable after my Austin Healey 1:1 angle drive to power a 4:1 clockwise tachometer I’d seen on e-bay.

I looked for g/boxes but all were as expensive as the 4:1 reversing angle drive original to the gold star.
Then I thought of making my own box from meccano gears but perhaps a bit too ambitious for a neat solution.

An e-mail prompt from e-bay showed me first a 4:1 clockwise tachometer, then a 2:1 clockwise, then a 4:1 anti-clockwise, and then eureka, a 2:1 widdershins (anti-clockwise) tachometer for an incredible cheap £16, probable cheaper than the cable I’ll need to drive it.
So I hope I’ve got this right. The magneto turns anti-clockwise at half engine speed, my Healey angle drive turns this 90Deg non-reversing with a straight cable into the back of a 2:1 anti-clockwise tachometer.

Muskrat warned me about drag on the auto-ignition advance mechanism, so thank you. I had to look at my auto-advance to see why.
I understand it now but don’t want the expense of changing to a manual magneto especially as I plan to only adapt the points system on mine
to switch a SparkRight electronic unit, another cheap modification using parts I have laying around. You may see a trend here when it comes to spending money, but many kids and even more grandchildren, car projects, house maintenance and shiny bits for the plunger all take a toll on my little pension.
So I looked again at my auto-advance system and think I could mount a square pin needed to drive my angle-drive onto the four stops that limit the movement of the bob-weights under centrifugal force at high speed negating any drag from the cable on the armature.
I’ll have to accommodate access for a spanner to the nut and allow easy coupling to the collar I’ll turn up of my lathe that will be mounted on the timing case cover to hold the angle drive.
So I need to stop talking about it and actually do something.
Thanks again,
Steve.

[TT John]

I believe that electronic tacho's are available, not quite sure who sells them but I have seen them.

TTJohn

[Steveba10]

Hi john,
You are right about electronic tachos being available and I have several off of cars.
None that I know of are 6v though.
I just wanted to replicate the system I had on a B32 back in the sixties without the expense that buying the parts today would entail.
Plus I enjoy making something for next to nothing rather than just pointing a credit card at it.
Steve.

[berger]

 *conf2*what's a credit card

[Steveba10]

Hi, I’ve finished thinking and actually did something about it.
I set the casing on a face plate after drilling the translated position of the timing gear centre and then turned a hole to hold the mount for the angle drive.
Then used an old brass pipe fitting for the mount, cutting a thread for both the clamping nut and the angle drive, adding a clearance hole for the short coupling pin. I used a piece of bright silver bar for the pin, drilling it and then pressing it square to take the input peg of the angle drive.
The other end of the coupling pin was filed to make a tendon. The locking nut for the mag drive was cut to make a mortise for the coupling pin.

Initially I wanted to keep the auto ignition timing function, I tried to make a bridge across the bob-weight limit stops for the drive but there was insufficient room between it and the casing given that a spanner is needed to set the static timing. So instead I’m going for manual ignition control but will keep the auto mag gear, locking the movement if the timing scatters due to the drag of the tachometer cable.

I’m pleased with the result, using an a spare Healey speedo drive I’ve had kicking about for 40 odd years, the cost has been minimal, just a cable and a cheap but nice tachometer from India.

All I’ve got to do now is assemble the rest of the bike.
Pictures below.
And yes I know the angle drive is upside down compared with the original Gold Star installation but that’s the way Austin had them made.
Steve.

[RDfella]

Nice work. Good old-fashioned belt drive lathe I see. Have a gap-bed Ajax of similar design - now relegated to wood turning for patterns or similar work.

[muskrat]

G'day Steve.
Well done mate. 
Cheers

[Steveba10]

Hi RDfella,
I rescued this lathe when a skip driver friend phoned me saying the boat yard where it had been abused for years was being flattened for the building of riverside housing and the lathe was going for scrap.
I took a trailer, found my friend but no sign of a lathe, the yard and boat house had been emptied. My friend said ‘look up’ and there was the lathe swinging I guess 60plus feet up on the end of a tower crane. They had winched it up through the roof and over the car park. When it came down it nearly flattened my trailer.
I took it home, took it apart, shot blasted it and gave it a coat of paint, new belts and single phase motor. I don’t know who made it as it had no identification.
It is worn from lack of lubrication but ok if you always approach from the same direction and noisy but powerful on back-gear.
The attraction was it’s gap-bed meaning I could swing car rear suspension uprights where my 8” Southbend ( lease-lend and no they can’t have it back ) cannot and my Myford 7 certainly can’t.
Also good as you can see for BSA timing covers.
I’d like to get hold of a BridgePort Mill but either to expensive, broken or to far away so far. I live in hope.
Thanks for reading,
Steve.