Tachometer ratio

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Tachometer ratio

Postby Markiswellbe » Sat Apr 18, 2020 1:40 pm

I have a 1964 XLCH with magneto. I don't know, and was hoping to get the answer I need from someone here. I would like to know the ratio that the magneto turns the cable, and the direction it turns, so I can match up a tachometer to it. Does the Smith's tachometer that I believe to be correct turn counter-clockwise? Would a 1965 Stewart-Warner tachometer work? (I have one of those). Thanks in advance for any info. This is a great site and I am happy to be here. Mark
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Re: Tachometer ratio

Postby Markiswellbe » Sat Apr 18, 2020 10:06 pm

I have got the rotation figured out.
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Re: Tachometer ratio

Postby murph » Tue Apr 21, 2020 5:07 pm

Your tach and set up would look like this.

Image
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Re: Tachometer ratio

Postby Ferrous_Head » Tue Apr 21, 2020 6:45 pm

Uhhm, maybe not.

He has an XLCH.
It should have the Magnetic (RSM) version of the Smiths tach.

Picture shows the Chronometric version (RSC) which was used on the XLR.
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Re: Tachometer ratio

Postby murph » Wed Apr 22, 2020 2:48 pm

No, Actually the 1962 to 1964 xlch came with the chronometric tach.

http://www.harleykmodel.com/literature/ ... B_0619.pdf

You will also find it listed on page 80 of this parts book on the literature section right on this site, item #51.
1965 - 99451-65
July 1964
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Re: Tachometer ratio

Postby Ferrous_Head » Wed Apr 22, 2020 4:32 pm

You are correct Triumph. Must have been 65 they went to the RSM.

The price difference between the chrono and the magnetic is going to make you wince though. The chron0's are going for 5 times the RSM's. And that's if you can find one.
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Re: Tachometer ratio

Postby Markiswellbe » Wed Apr 22, 2020 5:40 pm

What makes the cronometric worth more than the RSM? I found a cronometric for $700. Can I use either one?
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Re: Tachometer ratio

Postby Ferrous_Head » Wed Apr 22, 2020 7:48 pm

In my opinion the chronometrics really aren't worth it.

The chronometriucs are made like a clock. The have gears which are turned by the input cable so they will be accurate. More accurate than a magnetic instrument.
The magnetics have a magnet that is spun by the cable and the spinning magnet drags the indicator around the dial (magnetic coupling if you like). It ha a spring to stop it from "just spinning" but of course this is not a direct drive setup like the Chrono's. So they aren't as accurate.
What does that mean in the real world ?

Pretty much sweet bugger all. It might be useful running the bike on a dyno. It might be useful if you drag race and have worked out the exact RPM for launches and shifts. (although I doubt that even).

I run a tach on my race bikes. The ONLY time I ever use it is coming off the line. And even then it's more for reassurance than anything else. I can get by fine without looking at it.
Almost no one ever looks at a tacho while riding. It's actually a dangerous thing to do if your traveling at speed.

You can run the RSM's. You can even run the Veglia's from 1970 - that's what I run on my race bike now. They are very cheap. $50-70 brand new on Ebay.

The other thing is the chrono clocks change in discrete steps - like the second hand on a digital clock. The magnetic's do a graceful sweep of the dial.
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Re: Tachometer ratio

Postby Markiswellbe » Wed Apr 22, 2020 8:42 pm

Well, I have been schooled ! And explained so well. I pretty much wanted to put a tach on my bike for looks, and a tach would do it. I have been drooling over the pics on this site. I thank everyone for the help and comments.
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Re: Tachometer ratio

Postby Ferrous_Head » Wed Apr 22, 2020 9:30 pm

The tach on my race bike is mostly there to impress the spectators.

Makes it look like a REAL race bike !

Without the tach it looks like any other run-of-the-mill ordinary Period 3 Unlimited Sidecar.
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