panhead rpm

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socalrider
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panhead rpm

#1

Post by socalrider » Sun Jun 06, 2010 6:50 am

what can i use to get an accurate rpm reading on my 65 pan. cant find a dwell/tach meter that works with 2 cylinders.
gracias
arnulfo
los angeles



steve_wood
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Re: panhead rpm

#2

Post by steve_wood » Sun Jun 06, 2010 10:22 am

Okay, here's what I think. Can anybody confirm?

The panhead engine produces a spark for each plug every revolution (the "wasted spark" phenomena). A normal 4 stroke engine produces a spark for any given cylinder once every 2 revolutions. A normal 4 stoke engine with 4 cylinders will produce two sparks (in total) for every revolution.

If your tach/dwell meter is connected to the spark plug wire of a cylinder, then take the output of any tachometer and divide by two.

If your tach/dwell meter is connected directly to the coil, then set it for 4 cylinder and multiply the output by 2.

DuoGlide62
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Re: panhead rpm

#3

Post by DuoGlide62 » Sun Jun 06, 2010 12:14 pm

OR, you could try to find an early shovel mechanical tach.
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RussW
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Re: panhead rpm

#4

Post by RussW » Sun Jun 06, 2010 4:10 pm

Here's a link to how I mounted a Tiny Tach setup on my '61, works pretty good. A lead wraps around one spark plug wire.
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Bosheff
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Re: panhead rpm

#5

Post by Bosheff » Sun Jun 06, 2010 6:51 pm

Sportsters used the same cable drive tach from the 64 to at least 71 or 72 if memory serves me. They also used centrifugal advance timers which used the same cap (top) as the 65-69 FL/FLH's used. Most of these tachometers didn't last long due to the vibration factor. So, if ya want one of these set-ups, the easiest way to find everything ya need it to rob the parts from a Sporty. I have been told that not all centrifugal advance Big Twin timers from 65-69 have the square hole in the top of the shaft to mate with the cable adapter, but I have never seen one that didn't.....bosheff

socalrider
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Re: panhead rpm

#6

Post by socalrider » Mon Jun 07, 2010 12:33 am

thanks for the help guys.think im going to go with the tiny tach.inexpensive and readily available.
arnulfo

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Re: panhead rpm

#7

Post by RooDog » Sun Nov 11, 2018 2:09 pm

I have used genuine Harley electronic tachs with no problems. And your's being 12 volt they should work just fine too. 12V +, Ground, a lighting wire, and a signal wire to the points side of the coil. Most any electronic tach from the late 1970s through the mid 1980s should work, either big twin ( FX models are good donors) or Sporty will work...... They're usually cheap on eBay or at swap meets. You just don't want one from the very earliest 1970s as they run off of the old 4 wire alrernators, and the latest ones with factory single fire should be avoided too.....
RooDog

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