The original spark plug washers (#2 here) were copper lined with asbestos insulation. I've found them above and below the porcelain on some plugs, and only below on others. I'm not sure how they came originally. A problem is that you can't get new ones.
Being unable to find any new washers of the original type, I'm trying copper crush washers. I can use them above and below the porcelain on the earlier plugs, but only below on the later ones because they wont fit over the brass caps. I'm hoping one underneath will be enough for the later plugs.
Running my fresh engine to heat up the oil for a change and to retorque the head bolts, over the sound of the idling engine I heard the telltale sound of a compression leak.
Soot on the insulators tells the story. I have to be careful tightening down the collars. I want to get them tight enough to seal, but not enough to break the porcelain. I suppose this will be like the head bolts. Tighten them until just before they break.
(Message edited by steve_jelf_parkerfield_ks on January 27, 2015)
Looks like the the washer on top would make no difference as far as sealing at that point. It will leak past the treads in any case. A soft washer on the top may be a benefit by allowing the load on the porcelain to be spread out and allow the clamping collar to be tightened tighter without breaking the porcelain.
My thought too. I'll use washers under and over where I can, and only under where I have to, and see if it makes any difference.
Yikes! Is that what they're selling for thumbscrews these days?
Are the seals solid copper or are they U-shaped sheet? If solid, I would anneal them first to get them dead soft.
Annealing (as Ken K says) may help. But I suspect this will be a case of re-tightening after (or even while) running a few times until the leak stops permanently.
I like the thumb nuts .Homemade look good to me.
Crush gaskets crush because they're soft.
Tom is correct. The thumb nuts are home made without the tools to do them right. I made them because I could never find any with the correct 5-40 thread. There are plenty of 8-32 for the later plugs, but I haven't found a source for these.
Did you check here Steve ?? they list 6 sizes.
Yep. No 5-40.
Any kind of sealer useable here? Agree that the top ring would probably protect the porcelain as opposed to doing any sealing.
I was wondering about that too. It would have to be something that could take the heat.
High heat red RTV.
How about making upper sealing washers out of soft aluminum? You could punch them out w/round gasket punches.
What crush washers are you using? Where do you find them?
1/2" id, 3/4" od, from http://www.gen-aircraft-hardware.com/
Would that be #MS35769-9?
Yes, those are the ones.
If I remember correctly, one of the Ford books showed the plug being held by the collar and the wrench turning the larger base of the plug to tighten. Like other posters, I have found washers on both sides of the porcelain.