"measure the gap with a feeler gauge"
that's exactly what I did, I measured the gap with a feeler gauge by laying my square against the head. I could clearly see the amount of light shining through the gap.
I thought I was being quite clear about what I meant.
I thought 5mm is the same thing as 5/1000. I thought mm is 1000. When you say 20/1000 is a lot , hmm I gap my front mount distributor @ 15 ,side mount distributor @25, spark plugs @25 , doesn't seem like a lot to me. I may be wrong, I'm just a back yard N tractor mechanic.
2N with 8N motor 8N345567