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+--- Thread: Indian-made motorcycle speedo and tacho (/showthread.php?tid=9969)
Indian-made motorcycle speedo and tacho - falcott - 25-04-2025
Hi all, I have an anticlockwise 2:1 chronometric tachometer and a matching speedo ("Smiths" on the faces, but made in India nonetheless) and I'm intending to used them in my Special. Has anyone else done this? -- particularly the speedo. Speedos are a black art for me, I literally have no idea about ratios or anything, whether or not there is a fixed ratio for speedos. How does one match up a speedo swap otherwise?
Also, does anyone offer a tacho drive conversion from under the distributer?
RE: Indian-made motorcycle speedo and tacho - Tony Griffiths - 26-04-2025
(25-04-2025, 11:49 PM)falcott Wrote: Hi all, I have an anticlockwise 2:1 chronometric tachometer and a matching speedo ("Smiths" on the faces, but made in India nonetheless) and I'm intending to used them in my Special. Has anyone else done this? -- particularly the speedo. Speedos are a black art for me, I literally have no idea about ratios or anything, whether or not there is a fixed ratio for speedos. How does one match up a speedo swap otherwise?
Also, does anyone offer a tacho drive conversion from under the distributer?
Well, I've never done it myself, but the builder of my Ulster Replica did. He cleverly used a pair of decent-looking speedometers from a Ford 10, leaving one as a speedometer and making the other into a rev counter. To get them working correctly, he built onto the back of each a train of Meccano gears—having first calculated the effect of all those ratios built into the transmission system and, I suppose, the speedometer itself. I believe the calculations ran to a sheet or two of A4. He also converted the bottom of the distributor housing to take the rev counter drive using the speedometer cable from a Land Rover. Tony Betts used to do a conversion kit: www.7ca.co.uk/
If you can get hold of a copy of "A Guide to Building Reproduction Austin Ulsters" by Chris Gould, there's a section by Vinc Leek devoted to the problem you have including discovering the TPM - the turns per mile - of the drive cable. Another tip in the book is to contact your local Tachograph agent; they can supply small gearboxes for fitting to the drive cable to get the ratio correct. This company can convert your instruments and can also provide suitable parts to do the job yourself: https://www.speedograph-richfield.com/ Also, see this older "Friends" post: https://www.austinsevenfriends.co.uk/old_forum_backup/pub25.bravenet.com/forum/static/showf6fd.html?usernum=2099944454&frmid=5&msgid=1020047&cmd=show
and this one on revcounter drives: https://www.austinsevenfriends.co.uk/forum/showthread.php?tid=8777&pid=96357&highlight=revcounter#pid96357
RE: Indian-made motorcycle speedo and tacho - falcott - 26-04-2025
Thanks, that's a start. I have Chris Gould's book and I've read about half of it. Tony Betts no longer does tachometer drive conversions so I'm still looking. And I'll look at the links that you've offered, thanks a lot.
RE: Indian-made motorcycle speedo and tacho - "Slack Alice" Simon - 26-04-2025
I used my lathe - which has a known speed of rotation - to drive an unknown speedo, to see how it performed in relation to a standard speedo.
So, for example, if the input from the lathe gives 30 mph on the speedo off my car, and 60 mph on the unknown speedo, I will need a 2:1 reduction gear.
RE: Indian-made motorcycle speedo and tacho - falcott - 26-04-2025
My old lathe was treadle powered, now powered by an old washing machine motor, so I've got no chance to mimic your success. But it does give food for thought. Thanks.
RE: Indian-made motorcycle speedo and tacho - "Slack Alice" Simon - 27-04-2025
You don't need to know the lathe speed, just the relative readings of the speedos.
Treadle would do it, if the flywheel kept the speed constant-ish.
RE: Indian-made motorcycle speedo and tacho - Howard Wright - 27-04-2025
Hi Both
If you have a smartphone you can get a strobe app which can tell you the revs. I did this when trying to calibrate a PA speedo. I didn’t use my lathe but a drill attached to the end of the speedo cable. Using the app I was able to determine the revs of the drill at full speed. Then to see what speed that produced on the speedo. From this I found that the speedo was from a car with a 5.25 axle when my car had a 4.9 axle no wonder it was way out!
I also tried an Indian rev counter on my special with the drive taken off the bottom of the dizzy. I think that I got the ratio wrong when I purchased it but then tried to correct it via a replacement dial (scanned and photoshopped). It was never really successful and I splashed out on an electronic rev counter from Willy MacKenzie. That works very well!
Cheers
Howard
RE: Indian-made motorcycle speedo and tacho - falcott - 27-04-2025
Thanks guys.
Is there any lead on getting a rev counter conversion from the distributer please?
RE: Indian-made motorcycle speedo and tacho - Howard Wright - 27-04-2025
Hi Geoffrey
https://www.austinsevenfriends.co.uk/forum/showthread.php?tid=4183&pid=44383&highlight=Rev+counter+drive#pid44383
Cheers
Howard
RE: Indian-made motorcycle speedo and tacho - falcott - 27-04-2025
Thanks Howard.