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Old 04-23-2003, 02:01 PM   #1
madmike
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Valve seats- how to tell if hardened or non-hardened?

A friend gave me a pair of "049" oval port big block Chevy heads that supposedly were gone through by some owner previous to him. I plan on using different valve springs to match my cam application, so I'll be pulling the valves and looking at the seats also. These heads were supposedly freshened up, so hopefully I won't have to spend a bunch of money on them.

While I am looking at the valve seats, how can I tell if they are the original, non-hardened for leaded fuel seats - or, if they have been replaced with hardened seats so that todays fuel can be run? As always, thanks for the info!
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Old 04-23-2003, 02:04 PM   #2
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Re: Valve seats- how to tell if hardened or non-hardened?

Well how old are they, all heads made by chevy from 1974 on had hardened exhaust seats. When freshended they don't normally replace the valve seats (if they did they would put hardended ones in, be stupid not to) they just grind them.
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Old 04-23-2003, 02:04 PM   #3
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Re: Valve seats- how to tell if hardened or non-hardened?

You usually can see a "ring" that was machined out and replaced with different material.

John
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Old 04-23-2003, 02:10 PM   #4
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Re: Valve seats- how to tell if hardened or non-hardened?

[ QUOTE ]
You usually can see a "ring" that was machined out and replaced with different material.

John

[/ QUOTE ]

This is true if aftermarket hardened seats have been installed by a machine shop. The factory just flame or induction hardens them. A lot of times you can see the metal discoloration around the seat area on a clean head if they were flame hardened at the factory. I think by 1972 or so, GM was flame hardening the seats in preparation for the phase-out of leaded fuel. What date code is on the heads?
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Old 04-23-2003, 02:53 PM   #5
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Re: Valve seats- how to tell if hardened or non-hardened?

I could be mistaken but I don't think OE big block heads have replaceable seats.
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Old 04-23-2003, 04:01 PM   #6
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Re: Valve seats- how to tell if hardened or non-hardened?

usually if the seat is clean it is very shinny if they are hardened.

[ QUOTE ]
I could be mistaken but I don't think OE big block heads have replaceable seats.


[/ QUOTE ]
a machine shop machines the old seats out and then presses the new ones in
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