How to tell if older heads have hardened seats... - Chevelle Tech
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post #1 of 6 (permalink) Old Apr 16th, 08, 2:58 PM Thread Starter
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Jarrett
 
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How to tell if older heads have hardened seats...

Found a set of 091 camel hump heads on craigslist in my area for what I think is a decent price - $250 and supposedly price is not firm. Owner claims they have been recently rebuilt (he bought them this way) and "ready to bolt on".

Is it possible to tell if an older set of heads has been updated with hardened valve seats? Anything else I should look for if I got to take a look at them? OR is my only option to have a machine shop look at them?

Any help is appreciated.

Thanks in advance.

Jarrett
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post #2 of 6 (permalink) Old Apr 16th, 08, 3:21 PM
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Re: How to tell if older heads have hardened seats...

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Originally Posted by 300Deluxe View Post
Found a set of 091 camel hump heads on craigslist in my area for what I think is a decent price - $250 and supposedly price is not firm. Owner claims they have been recently rebuilt (he bought them this way) and "ready to bolt on".

Is it possible to tell if an older set of heads has been updated with hardened valve seats? Anything else I should look for if I got to take a look at them? OR is my only option to have a machine shop look at them?

Any help is appreciated.

Thanks in advance.

Jarrett
You mean 291's

Yes, you may be able to see the outer edge of the false seat. It should extend about .050 outside the valve. The seats I put in are 1.562 so it's even less. This is the most common size put in the small blocks.

I have a picture of a valve over the top of a seat but not sure if you can see close enough in the pic to see the seat. I can see it in the pic though. You can use a small wire brush to scrub away some of the carbon around the exhaust valve and may be able to see it on the heads you may get, if they are used. If new, should be easy.

Hope it helps.



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post #3 of 6 (permalink) Old Apr 16th, 08, 4:34 PM Thread Starter
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Re: How to tell if older heads have hardened seats...

"You mean 291's"

Yes I did. I apologize.

Thanks for the response and pics. This will help me a lot.
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post #4 of 6 (permalink) Old Apr 16th, 08, 4:35 PM
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Re: How to tell if older heads have hardened seats...

Good luck

1968 Chevelle Sb
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1973 SS 454 Chevelle
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1955 Delray LS1
1967 Nova 496
1969 nova 427
1969 Camaro 350
1968 Camaro Convertable 350
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post #5 of 6 (permalink) Old Apr 16th, 08, 8:55 PM
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Re: How to tell if older heads have hardened seats...

I think, "THINK", some head's seats after '71 were induction hardened and all after like '73 are!

So you need to check date codes and to be sure, your Machinist will know when he does a valve job on them. GM knew unleaded gas was coming so started early here to account for it.

I don't think -291's are hardened so installed seats will be the way to go.

pdq67

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post #6 of 6 (permalink) Old Apr 16th, 08, 9:46 PM
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Re: How to tell if older heads have hardened seats...

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Originally Posted by pdq67 View Post
I think, "THINK", some head's seats after '71 were induction hardened and all after like '73 are!

So you need to check date codes and to be sure, your Machinist will know when he does a valve job on them. GM knew unleaded gas was coming so started early here to account for it.

I don't think -291's are hardened so installed seats will be the way to go.

pdq67
1973 heads would be the 993's for the 1.94's and did not have the hard seats or at least wasn't good enough to tell. I've done dozens of them and they are soft. 882's did have the inducted seats but are crappy heads. The problem with the factory seats is they get hairline cracks and eventually crack all the way. A properly installed false seat is best.

1968 Chevelle Sb
1969 Chevelle 496
1973 SS 454 Chevelle
1974 S-3 454 Chevelle
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1967 Nova 496
1969 nova 427
1969 Camaro 350
1968 Camaro Convertable 350
1968 Camaro Coupe 427
.
http://tcnwracing.com/
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