Points opening specs??

On the Fairbanks Morse Magneto Type FMJ I've been working on, what should the gap be when the points open?
Thanks
Ryan in Northern Michigan

Well first off if you do not have a manual for that mag send me an e-mail and I'll send you one. I have it on the computer so cost to you is your time. As for the point setting if I read this right, I don't have my glasses on it says 0.022 or is that 0.020. Now see you went and made me get up and get my glasses and it is 0.020. LOL

Dang, all this time I thought it was the thickness of a bookmatches cover, now you"re saying I need to use a feeler gauge? LOL

old whats your email address. Manual would really help.
Thanks

Did you check out the link I previously posted to the FM factory manuals, or isn't point gap covered there?
FM

FMJ gets set to .020" and uses a .19 microfarad capacitor.

FMX is .015" and RV4 is .012"

Wico A, AH, AP, APH, C, XH, XHD, and XV are all set to .015"

You mean it is not. I saved all these book match covers for nothing.

Bottom right corner of my post will have send e-mail just click on it and it will set you up to send me an e-mail so easy even a 5 year old can do it. Got tired of the cave man thing LOL

Well if your out in the field and it stops running a match book will do the trick or for that matter the box the points come in work well for setting them. Shoot back in the day I would eye ball them and that worked many many times but seems any more my calibrated eyes are loosing calibration and I can't seem to find any place that will re-calibrate them LOL

No, no, its an eighth inch up from the sharp edge of the big blade on my pocket knife. Spark plug gap is a quarter inch.

No joke. When I was with the Phone company we came across a relay adjusting procedure that said "guage by eye." Some dummy (Back then we could call them that.) started looking for an eye guage.

Ryan, This is more info then you wanted and many people never heard of it and the readily obtainable specs as listed below will get you in the ballpark and she will run fine. HOWEVER if youre a perfectionist and want to realize the absolute maximum spark energy available from a magneto, adjusting points using whats called the edge gap method is best as the listed specs are often only an approximation of what the points gap SHOULD BE if all is well and correct and theres not yet any wear and tear and slop, in which case that X amount of points gap yields the same as using the edge gap method of adjusting points, BUT NOT NECESSARILY SO AS A MAG BEGINS TO SHOWS ITS AGE.

How it works is there is a precise short distance after which the rotor magnets have exited the laminations WHEN THE COIL CURRENT IS AT ITS ABSOLUTE MAXIMUM and its precisely then the points should break open. What a person does is use a tool or jig to hold the rotor at that precise location then slowlyyyyyyyyyyyy open the points adjustment to stop JUST WHEN THEY BREAK OPEN. Before the points rubbing block is worn down and the bushings arent overly worn that condition is approximated by setting the gap to that typical 0.020 to.022 etc.

A friend of mine recently deceased was a retired Nuclear Physicist who had the time equipment and know how to set his that way and then had equipment to measure the results and he and I always had fun discussing this topic. He used to give a Mag seminar at Gathering of the Green prior to my giving them and I told my people heres the mag specs and what to adjust the points at BUT if youre NERD heres how Duane adjusts them lol then tell them how to use the edge gap method.

Sorry I dont have the FM manual but Bob there has ya covered on that and perhaps it describes how its done on those FM Mags

Best wishes n God Bless yall

John T

Some old fords, it was a thin dime. Bubba only had 2 nickels. Still on the side of the road.

That's like "press any key"

In the FMJ, .020" point gap automatically provides an .15" edge gap along with the called-for dwell angle, asssuming the moving parts aren't worn badly. If they are, he's got more to worry about then just breaker and edge gap. Impuluse working and timing? Bearings? State of magnet charge?

The idea of maximizing spark potential by edge gap instead of breaker opening/dwell angle . . . falls into the category of adjusting valve lash by valve timing degrees instead of measured clearance. Works for racing puposes but usually has little meaning for someone screwing around with a tractor. Even with racing, threre have been long arguments, some even written by Henry Ford.