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?

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

The plug tube does not serve as a crush washer—there's nothing to crush—and your starting problem was not caused by compression leaks past the plug tubes.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Do you think this damage is a result of too much torque? I have to admit the 30 ft-lb spec in the FSM sounds like a lot, to me.

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

I think it's a result of most spark plug tubes being between 43 and 57 years old.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

30 lbs for an iron head sounds like it's at the high end of permissible TQ.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

The ridge on the tube looks like it would match the slight countersink at the start of the thread hole in the head.

Lot's and lot's of removal and reinsertion and torquing would 'forge' the aluminum into the countersink...........

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes