RE: TR4A plugs

[Bill Babcock <BillB@bnj.com>]

I'd be really careful about extending any threads into the combustion
chamber. With the short working life of a racing plug (maybe) you probably
wouldn't get the usual problem of carbon depositing on the treads and
ruining the heads when you back out the plug, but the high temperatures
could melt the sharp tips of the threads with the same effect. Of course
these kind of worries are much more important with aluminum heads. I've seen
dozens of bike heads ruined by using the wrong plug. 

For that matter you can get detonation from the glowing threads.

Might not happen, but it would make me nervous.