rotor button and cap

can anybody tell me what the gap should be between the rotor ****on and the cap ? as i can only get a week spark from my magneto, iv'e had the maggy tested and is fine . i had a cracked cap and replaced it with a msd cap which mesures the same as my old one but the ****on seemed to touch the other cap points as there were marks on the old one and misses on the new one . i am having trouble finding a new rotor ****on the same as the one i have and the mst ****on i got with the cap has a different size hole for the shaft . any help will be appreciated

 

It wouldn't hurt to tell us what brand Mag you have and what engine it is in?

 

This is a blurry picture of a GM HEI distributor that I cut to measure the gap for what reason I don't recall. Was building a HEI for my 37 Buick straight eight so probably had something to do with that but who knows? The gap is surprisingly large <> 0.040 in thousandths. On my Sun machine each mag varies but usually have a weak spark till about 500 rpm where it matches a good conventional distributor spark intensity which is well above starter cranking speed. By 1500 distributor rpm (3000 engine rpm) a good mag will jump fire across a one inch or greater air gap which is above most regular distributors capability.

 

its a wico maggie with a pounden-gerde top on it . its on a flathead ford v8

 

Don't have much experience with the old flattie stuff, mostly Hunt or Scintilla plus a few more modern ones. I do know the old tractor mags would fire one off with hand cranking so they must have a decent spark just clicking over. Is the "stinger" exposed with the cap off? If so you could hold a ground near it and see how big a gap the spark will jump with each click and then put the cap on and see how big a gap is jumped from a plug wire. If a big difference then it's being lost in the cap/rotor which is pretty much what you suspect but this would prove it.

 

i have a big spark at the coil lead when earthed but will try what you suggested . maybe the new cap is ******ed two ?

 

Do you get good spark with the cracked cap?

 

Not out of the leads as the spark followed the crack around the inside of cap

 

Since the rotor won't fit, I ***ume you have the wrong rotor so it may also be the wrong cap. The rotor should touch the coil terminal in the center but it will have slight gaps at the plug terminals. Put some clay on the terminals and turn it over.