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panhead rpm

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panhead rpm


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.
los angeles

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Re: panhead rpm


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.

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Re: panhead rpm


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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Re: panhead rpm


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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Re: panhead rpm


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

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Re: panhead rpm


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.

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