I have a couple loose tubes. Is tightening the spark plug supposed to hold it down? I took one out to replace the seal and they won't seal. It seems that the threads on the spark plugs might be too long-i've tried a couple. I have oil leaking out so I'd like to get this figured out. Any advice appreciated.

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have a homebrew

The oil leakage is from the tube O-rings, but you should be able to tighten the plugs so the tubes don't turn. If the tubes are so loose that they turn, they are likely not compressing the O-ring properly either

Did you leave the copper gaskets on the plugs when you installed them? I've heard some people remove the gaskets and depend on the tube for a plug gasket. While that might work while the tubes are new, once they develop cuts and gouges, they won't do the job...if they ever did.

if you overtorque the sparkplug the bottom of the spark plug tubes will permanently deform and stretch.This will push the rest of the tube upward, creating a gap between the seal and the cylinder head.

You are only supposed to tighten the sparkplug to about 15 ft./lbs, or about 3/4 turn after finger tight. Not as tight as you can.

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I've been calling it as i see it for my entire life and that's not about to change. Take it or leave it.

The spark plug tubes on my Barracuda were loose when I got it. I tightened them up by peening the edges around the plug hole over. I put the tube over a deepwell socket that was a little larger than the flat area at the bottom of the tube and tapped it over with a hammer. Work around the outside edge of the socket. You will need new seals and they will weep a little oil no matter what-especially if your engine is worn and you are getting blowby.

The best fix is to get the later head without the separate tubes!

Have had same problem-replace the tubes-even with used ones.

Will

Inspect the tubes carefully, "peen" and file flat as needed or, as Will suggested, just find some good replacements.

The factory did not use the spark plug's standard gasket and the design relies on the base of the tube to make the seal.

The use of the sparkplug's standard gasket (sealing ring) along with the tube can cause the problem you have. When both are used, the plug does not screw all the way into the combustion chamber, leaving a couple of threads exposed to the burn.
The exposed threads quickly fill-in with carbon deposits so if you go to install a new set of plugs without the gaskets, the plug will not seat completely and leave the tubes loose. Another result of using the sparkplug gasket is that it is a thin ring and puts a lot of localized pressure on a small amount of the soft alm. tube's sealing area. The end result is that this distorts / smashes a big dent into the sealing surface of the tube, making them had to seal the next time.

One "fix" is to pull all the spark plugs and run a 14 mm tap thru all the plug holes, this gets the carbon out of the last few threads. (coat the tap with some grease to "catch" / hold all the crud)

With new o-rings, re-chased threaded holes and decent tubes, you should have no trouble getting these to seal.
DD