adding a tachometer

I am wondering if anyone has added a tachometer to a 1997 Yamaha
Virago 535. If not how hard is it to add one anyways. I've heard
positive and negative sides of the coil??

Joe

 

There are plenty of aftermarket electronic tachs you can fit, usually
sold for racers or custom bikes. Yes, very easy to fit. They look pretty
crap, mind.

Oh, and you might have illumination in it which would have to be plumbed
into the lighting circuit.

 

You can normally run a tach off the negative primary
lead from an ignition coil.

The trick is figuring out how many revolutions per spark
on your bike and buying a tach that's set up accordingly.
I like tachs designed for HDs because they're dirt cheap
and there are a zillion of them out there.

My older BMW airhead generates one spark per engine
revolution, so I run a cheapo eBay tach designed for
an HD "dual fire" ignition. If the coil were generating one
spark for every two revolutions, I'd go for a tach designed
for the HD "single fire" system.

If you wanted to wuss out, you could go for a slightly
more expensive tach that's designed specifically for
your bike, then follow the manufacturers instructions to
install it. Takes all the fun out of it though.

 

i was going to go for a 39.95 tach from jc whitney. its chrome and
goes up to 12k.
http://tinyurl.com/3xvtdx

 

If I'm reading it right, that's a mechanical rather than an
electronic tach. For a '97, I'm pretty sure you want electronic.
That looks like the wrong stuff.

Also, does the engine really go to 12k ? Kind of a waste if
the tach goes to 12k and the engine's toast at 8 or 9k.
Better to buy one that matches the engine's top RPM
plus a very tiny bit extra.

 

well its a mechanical speedometer. so i figured id put a mechanical
tach

 

Then you are entering a world of difficulty.

 

What had you planned to connect the cable to ?
(Besides the tachometer).

A mechanical tach or speedo uses a mechanical
drive cable hooked to the engine or drivetrain which
spins a magnetic disk in the instrument, which
in turn pulls against a spring to move the needle.

An electronic instrument counts electric pulses
coming from the ignition coil or a sending unit.

Unless the machine has a hookup point for a mechanical
tach cable so you can drive the tach, trying to install a
mechanical tach would be difficult.

You could always use some kind of had crank I suppose,
but it would be difficult to crank it at the same speed as the
engine. Spagthorpe experimented briefly with this design
before they went to a hydraulic tach.

 

Have you *only* just realised this? Of course it didn't. The bike's been
around for two decades.

The 535 is a one-off engine. The chances of parts from the 750 (which is
the nearest in capacity) are remote, to say the least.

This has nothing to do with his problem.

Cable drive works pretty well for tachos. I can't remember the last time
I had a tacho cable snap. But an electronic unit is a neater solution,
agreed.

 

Spagthorpe's trouble was that Germany was the only source of hydraulic
tacho oil. At the outbreak of WW2, supplies were cut off.

 

No, the tach cable will be turning considerably slower than the cam,
*never* at the same speed if a worm drive is used.

Worm gears (from porous memory) typically have a *minimum* reduction
of about 3 to 5 and can go considerably higher.

Wiki says 10:1 to 100:1 is the typical range of a worm gear reduction,
so a mechanical tach cable driven by a 10:1 worm gear off a camshaft
on a 10,000 rpm engine would be running at 500 rpm max.

http://en.wikipedia.org/wiki/Gear#Worm_gear

 

Which is where we came in.

 

message

It would be easier still to simply forget about the tach altogether. Why
would one possibly need a tach on a vtwin cruiser, especially a small
displacement, low power vtwin? Like teats on a boar

 

Well, yes, except that sometimes even I like to check an engine revs.

 

Today though, any high quality synthetic blinker fluid should
work fine provided you backflush regularly to prevent varnish
buildup.

Hope this helps

 

True, providing that you can find a pre-war Spagthorpe hydraulic tachometer.
They had a real quality control problem for a few years after the war
started. The military were drafting every skilled workman they could find,
and Spagthorpe had a lot of trouble hiring quality workers to man their
instrumentation division. For several years in the early 1940s it was
virtually impossible to hire a competent tach welder.

-Scott

 

OMG, no no no...

The problem was drawing paper sizes... you cannot properly draw a round tach
on portrait paper.... you need landscape paper to do that.. and that hadn't
been developed at that point...

Jeez...

P.