Tool time math quiz.

[Geo-TH,In]

My digital tach measured 3000 sparks being generated by the Magneto on my 4 cylinder Farmall C each minute.

How many RPMs is the crankshaft turning?

To keep the quiz simple, let us say for every 3 revolutions of the crankshaft the PTO makes one revolution. Which I used my antique Steward Warner mechanical tach to measure.
What is the RPMs of the PTO when the mag is producing 3000 sparks per minute?

I had to measure all the sparks generated my the mag, because the mag produces a very strong magnetic field I was getting crazy numbers when I tried to measure just one spark plug.

Isn't math fun?

If I asked my Oldest granddaughter, who is a Jr at Purdue, if math was fun she would reply, Grandpa I don't do math for FUN!

Are you mathematically challenged like my granddaughter and my daughter?

 

[Janicholson]

500 + or - 1500 rpm Jim

 

[Mike(NEOhio)]

How did you count 3000 sparks?

 

[Geo-TH,In]

The electronic tach counts the number of sparks per minute at the mag, then you need to convert that to RPMs. The black wire wrapped around the spark plug wire coming out of the mag picks up a pulse each time a spark is produced.

 

[Mule Meat]

No one can give you an answer without first asking..
Does the Mag fire only on the compression stroke?
Or
Does it fire on both compression and exhaust stroke?

One will have a 1000 rpm PTO
The other will have 500 rmp PTO

 

[Brown David]

Never mind.

This post was edited by Brown David on 10/20/2023 at 03:47 pm.

 

[john in la]

Half the cylinders in a 4 stroke engine fire on the same revolution.
A 8 cylinder fires 4 times per revolution and a 4 cylinder fires 2 times per revolution.
So a 4 cylinder firing 3000 times is turning 1500 RPM.

 

[sotxbill]

Then... your recording 3000 sparks off of one spark plug.. so that would change the answer by a factor of 4.... if there is a cap with 4 plug wires and a rotor on it on the magneto and your sampling just one wire...... SO thats a huge change in the info... 3000 sparks off of one wire equals 1500 rpms on a 4 stroke....divided by 3 would mean 500 pto rpms...

 

[JMOR]

More guessing what he has than math , for sure! :shock:

 

[john in la]

3000 sparks off the coil would be 1500 rpm

3000 sparks off one plug wire would be 6000 rpm.

 

[sotxbill]

Your right.. I went the wrong way..3000 sparks off one wire/cyl on a 4 stroke.... would be 6000 rpms... ouch.. thats really fast for an tractor engine. Whats wrong here? balanced crank and pistons? makes me wonder if its now a 2 stroke??


or is there a tach that is converting to real rpms???3000 real rpm divide by 3 equals 1000 pto rpms? where 1500 real rpm would put it at 500 pto rpms.. now that sounds more in the ball park.

got to wonder where he's getting his spark count from and is it converted... I dont see the engine running very long at 6000 rpms at 3000 sparks on one cyl.. but then maybe as others have said.. It sparks on the compression and on the exhaust cycles. that would put this back in line.