sparkplug reach

[TokyoJoe]

How can I measure what the correct reach sparkplug should be?

Motor is a 420w (4.10 x 4.040 6.2 rods)
AFR 225 heads 58cc

 

[junkyardwarrior]

14mm thread, 3/4" reach.

Probably start with an Autolite 3924 or 3933 for a gas natural aspirated deal. 3933 is a race plug with trimmed strap.

 

[TokyoJoe]

I've got a set of ar3933's but they are a .750 reach plug. I pulled .50 reach plugs out of the motor, thats why I am asking how can I measure maximum reach or correct reach that I should be using?

 

[tannerc91gt]

this is just thinking out loud here as i honestly dont know the legit way to do it but if your concern is piston contact couldnt you just clay them like you would when checking PVC and see if youre getting any contact? shouldnt do any damage to the piston if youre just hand turning it and you should be able to see how much you can get away with that way

id love to know the professional solution

 

[TokyoJoe]

thats exactly what I was thinking of trying but when you clay for PTV clearance the head is off...if you clay the plug it will just come off when you try to thread it into the chamber I would think. So I guess the correct way would be to pull the head then....?