I have a set of 73 #336781 heads How can I tell if they have hardened valve seats?

It's real easy to tell by just looking.
Normally they will only be on the exhaust side & will look like an insert a little bigger in diameter than the valve & about 1/4" deep into the head.

What about the induction hardened seats that were popular in the early 70s? How could they be identified? I know that they looked blue when new, but have no idea how to identify them after they have been used. There was no insert to see.

Good question. I have a set of late 1972 heads. I'd like to know if they have hardened seats or not. Anyone know when GM used hardened seats across the board?

Mike

Starting in '71 all Chevy engines were designed to run on unleaded gas. They had induction hardened seats rather than inserts.

Originally posted by Keith Tedford:
Starting in '71 all Chevy engines were designed to run on unleaded gas. They had induction hardened seats rather than inserts. Actually I believe GM started in 1974 & it was not all heads.
The early induction hardened heads are very prone to cracking in the exhaust seat area, especially in small blocks.
They also varied widely in depth of hardening & some will go right through the hardness on the first valve job.
If you have cut a few you will know as soon as you cut them if they are hardened & also when you go through the hardness & it will not always be around the whole seat.
We have put in a lot of hardened inserts but always advise the customer especially on rats that there is a chance of hitting water when installing the seat.
Small chance & in 30+ years I can't remember how many sets that were a problem, possibly 5 or 6 out of hundreds of sets of heads but it does exist.
Now,,, 348's & 409's are a different story :D
I will not put seats in these heads.

I have a set of 402 Hi-Perf PASS heads and I chose not to have hardened seats installed.

I read they can get ruined cutting them..

Would really like some more input.

Originally posted by Crazyhorse:
I have a set of 402 Hi-Perf PASS heads and I chose not to have hardened seats installed.

I read they can get ruined cutting them..

Would really like some more input. =
If they are installed properly I don't understand what you mean by ruining them :confused:
Unless as I said you hit water which is highly unlikely but is possible in any casting as you can't know for sure where the water jacket is.
Sonic checking at this point is very difficult due to the shapes & complexity of the casting.
Again, as I posted before, out of hundreds of heads I have had maybe a half dozen with a problem.