I noticed this the other day when I was changing spark plugs on the Race Dart. All 6 spark plug tubes have material squished out where they get tightened against the holes in the head. Not sure if it's from over-tightening or just from a long history of cycling at the correct torque. FYI, the FSM calls out 30 ft-lbs. My new NGK GR5s say 18-25 on the box, but that would be WITH the included crush washer. As this is a '64 head, I have always removed the crush washer on plugs that came with them.
Here are some pics. The tube on the left I pulled off the racecar, the one on the right is from a spare set I had laying around. The "squished" tubes also had tight enough holes on them that they had to be threaded on and off the plugs. The other set were loose enough to slide right onto the plug.
(Ha, I just noticed the pack of assorted crush washers laying on the work table in the background... apropos?)
I assume that since these tubes basically act as a crush washer between the plug and head, over time they will get cold worked enough to prevent proper sealing. Maybe that lip causes a sealing problem as well. I wonder if this was contributing to some of the starting issues I've had recently, i.e. poor sealing at the plug leading to low compression?
