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Measuring RPM on a Magneto Tractor

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Steve W (NY)

09-01-2004 11:34:35

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My BN has a magneto. I'm trying to adjust the RPM's to match what the book says. It feels as if it doen's rev enough.

I have a Dwell/tachometer, but it's for a distributor ignition. Is there any electrical way to hook this up to my current mag? And if not, how do you determine RPM on these old girls.

Thanks
Take Care
Steve

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El Toro

09-02-2004 17:58:26

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Re: Measuring RPM on a Magneto Tractor in reply to Steve W (NY), 09-01-2004 11:34:35

Hi Steve, You can find that engine speed if you know someone with a strobe light. You mark the damper pulley with chalk and keep adjusting the
strobe until the chalk mark appears stationary
on the pulley, then read your rpm's on the meter.
Good Luck, Hal

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Gene

09-01-2004 22:27:18

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Re: Measuring RPM on a Magneto Tractor in reply to Steve W (NY), 09-01-2004 11:34:35

Just set the BN by ear so that it idles well/smoothly, then will accelerate without hesitation.

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Wayne Swenson

09-01-2004 20:05:54

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Re: Measuring RPM on a Magneto Tractor in reply to Steve W (NY), 09-01-2004 11:34:35

Simplest method I know is to use a hand held tach that you hold against the PTO or belt pulley.
Do the ratio calculations to see if your engine is up to "snuff"
If my memory serves, about 585 pto rpm is what an H runs when wide open & no load. Should run 540 pto when loaded down on a dyno.
The little Vibra-Tach works ok also.

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Mike Mauck

04-08-2005 10:20:14

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Re: Measuring RPM on a Magneto Tractor in reply to Wayne Swenson, 09-01-2004 20:05:54

I wish to find a "reed tach" or "vibratach" to purchase. Who makes these instruments for sale today?

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lee

09-01-2004 16:43:26

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Re: Measuring RPM on a Magneto Tractor in reply to Steve W (NY), 09-01-2004 11:34:35

Do a temporary coil ignition conversion. You'll need an automotive ignition coil 6 or 12 volt,
an appropriate battery and some wire. Disconnect the mag coil internal to the mag at the points and connect up the ignition coil. Put a temporary switch in between the coil and bat or just use a jump wire. Observe proper coil polarity. Disconnect the mag high tension wire to cap and swap in the automotive coil wire.

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QWE

09-01-2004 15:27:29

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Re: Measuring RPM on a Magneto Tractor in reply to Steve W (NY), 09-01-2004 11:34:35

How about an induction pickup tach that
clips around the spark plug wire?

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Tractor Dan

09-01-2004 14:52:12

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Re: Measuring RPM on a Magneto Tractor in reply to Steve W (NY), 09-01-2004 11:34:35

i have a syro meter you just hold it on the side of the engine and play with the dial till the wire is in rythim and you have your rpms a old friend gave it to me and i first tried it on a couple defferent engines with tach to check it and its darn close

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Jokke

09-01-2004 14:22:00

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Re: Measuring RPM on a Magneto Tractor in reply to Steve W (NY), 09-01-2004 11:34:35

try builing a DIY wireless tachometer.
This is also an option for those who know there way around electronics or have someone buld it for you. Found one a while back on the www.
Link

Don't know how good it works, but the concept is good. I'm planning on building one myself.
Well it was just a tought, see what you make of it.

C ya

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Kevin (FL)

09-01-2004 12:38:11

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Re: Measuring RPM on a Magneto Tractor in reply to Steve W (NY), 09-01-2004 11:34:35

Steve,

Can't help you out with the dwell/tach hook-up on a mag engine, but soon we'll have to figure the same thing out on our AC B model. As a work-around, you can borrow a strobe tach from someone and use that. To use one of these you will need to put a piece of reflective tape on the crankshaft pulley or any other pulley that has a 1:1 ratio with the crank.

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Bob M

09-01-2004 12:33:59

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Re: Measuring RPM on a Magneto Tractor in reply to Steve W (NY), 09-01-2004 11:34:35

Steve - A few tach/dwell meters will work on a mag system, though most probably will not. (My Mac Tool tach/dwell will not...)

To connect, ground one meter lead and connect the other to the kill terminal on the side of the mag.

A couple other ways to measure RPM:

Buy a "Tiny Tach". These work by induction - a sense wire is wrapped around one plug lead and will display RPM whenever the engine is running. (Added bonus - a Tiny Tach will record engine hours and display accumulated hours when the engine is shut down)

Low budget method: Run another 4 cylinder engine alongside your BN and synchronize the RPMs of both by ear. Then use the tach/dwell on other engine (or other engine's tach if it has one...) to determine the BN's RPM. ...Bob

tiny tach

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Rob in Ore

09-01-2004 16:52:19

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Re: Measuring RPM on a Magneto Tractor in reply to Bob M, 09-01-2004 12:33:59

I have two of these. They work great for determining the maintenance interval on my mower and log splitter. However, when I tried it on my FAB w/mag it read from 800 to 1100 rpm as the full range of throttle. I assumed that it wouldn't work with a 4 cylinder engine. I know that my tractor has many problems; and my ears are not calibrated; but it sure sounded like there was more difference between high and low than what the tach was registering. The tach is so simple to connect I don't think I messed it up. What else could it be? Is my tractor really just 300 rpm difference from low idle to max governed speed?

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