The head I was planning on having ported, etc. has a crack in four of the exhaust valve seats. So I have a few questions that I'm hoping y'all can answer. First, does this happen often? This was a 3614850, 1974, head with the spark plug tubes.

Second, I know I want something that's post '68, but is there anything to avoid in the later solid lifter years? My machinist has offered up a 3698447-7. He says it has no air injection, but it looks from the chart at http://www.slantsix.org/articles/parts-matrix/jpg.htm like it should. I know the head I had did not have the air injection, but the chart makes it look like it should also. When did the air injection start? I'd rather not have the extra weight.

Also, is it common practice to install hardened valve seats in these heads when you install larger valves?

One more thing, the machinist has recommended positive valve seals on all of the valves. Is there a down side to this? I have a very old quote from Dan Stern about "locking up a valve" if you use these, but I'm not sure if that's still a problem.

Thanks.

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64 Valiant

Heads can crack. It doesn't happen terribly often on slant-6 heads, but it can happen.

The parts matrix contains errors; if there is a conflict between reality and the matrix, that's why.

The heads with spark plug tubes weigh less and allow you to remove the lifters without removing the head.

The first year for air injection was '72, but not all vehicles had air injection, so there were "with" and "without" heads clear up through the end of the '70s.

Hardened exhaust valve seats: a very good idea.

Positive valve stem seals: Perfectly fine if done right. I cannot remember ever having said you'd lock up a valve if you used them, though I know people who make this claim. If the valve stem-to-guide clearance is too tight, then the positive seals might not allow enough oil to this area and I suppose you could lock up a valve. Solution: Correct stem-to-guide clearance. On the other hand, the non-positive seals work fine, too.

Thanks Dan. That clears up a lot. The quote was something I pulled off the net (Mopar Mailing List ftp site) in 1997. Entirely possible you were misquoted.

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64 Valiant