When did GM start installing hardened valve seats in their heads? Were all heads treated equally....std small block heads to high performance big block heads? I'm especially interested in what might be found in flavors of 1977 era 454 high performance heads - closed or open chamber. Thanks
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Re: Hardened Valve Seats
Lonnie,
Since the General and all other domestic manufacturers started changing over to unleaded fuel in the early '70's, I would expect all engines would have had hardened valve seats in that time frame. I believe that 1971 was the last "leaded fuel" engine. That also coincides with the change from "Gross horsepower" to "net horsepower" in 1972. Just one man's 2 cents worth.
David Nims member #19639 save the wave ~~~~~~~~~~~~~~~~~~~ -
Re: Hardened Valve Seats
Lonnie-----
Chevrolet V-8 heads, both small block and big block, first received hardened exhaust valve seats for the 1973 model year. All passenger car and light truck applications used induction hardened seats and not inserts. With induction hardening, the substrate cast iron of the cylinder head is hardened in the vicinity of the exhaust valve seats. Inserts were used only for MD and HD truck engines and, of course, aluminum heads. MD and HD truck engines received the hardened exhaust valve seat inserts WAY before they came into use as part of the "unleaded gas" engines, way back to the 60s. Aluminum cylinder heads, although they received valve seat inserts on both the intake and exhaust valves were NOT hardened (until mid-80's aluminum small block heads). No PRODUCTION big block aluminum head ever received hardened valve seat inserts and SERVICE heads did not receive them until the current generation of GMPP cylinder heads.
The cast iron SERVICE big block head, GM #6260482, has induction hardened exhaust valve seats. However, this head was never used in PRODUCTION. The 73-74 Corvette big block PRODUCTION heads were oval port and of "open chamber" design. No PRODUCTION rectangular port big block cylinder head was ever used after 1971 and no PRODUCTION rectangular port cylinder head was ever produced with hardened valve seats.
By 1977 there were no big block engines being used in passenger cars. Those that were still being manufactured for vehicles were used for trucks only. None of these had rectangular ports or, even, the large oval ports used for 65-75 and none could be considered SHP or, even, HP engines. All PRODUCTION truck engines of the 76+ period used "open chamber" cast iron heads with "peanut" ports.
As far as SERVICE-only big block cylinder heads available in 1977, there were only 3 rectangular port, SHP cylinder heads available in the 1977 period. One was the cast iron GM #6260482 cylinder head which may carry casting numbers 6272990 or 14096188. As I mentioned, this was an open chamber cylinder head with induction hardened valve seats. It remains available from GM to this very day. The other 2 cylinder heads then available were GM #3919838 which was a closed chamber aluminum head with rectangular ports and GM #14011076 which was an open chamber aluminum head with rectangular ports. Neither of these heads used hardened valve seats. Both are now discontinued.In Appreciation of John HinckleyComment
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Hardened Valve Seats
Thanks very much for the response.
Yes, the specific head I had in mind is a '77 date coded pair of the open chamber cast iron service head. But I wanted the additional general info also. Very good answers...thanks very much.Comment
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Correction
After further checking I find that the GM #14011076 cylinder head was not available as early as 1977, but its predecessor, GM #3946072, was available at that time. GM #3946072 was discontinued in January, 1982 and replaced by the 14011076. The heads are similar and both are open chamber design, but the exhaust port configurations are different and the 14011076 has smaller intake runner volume than the 3946072. Neither head has hardened valve seats. The 14011076 was discontinued in August, 1995.
Also, the GM #3946072 cylinder head carried casting number 3946074. It was used in PRODUCTION for 1969 Corvettes with L-88 and ZL-1 and it was also used for 1971 Corvettes with LS-6.
The GM #3919838 closed chamber aluminum cylinder head that I previously mentioned that was still available in 1977 carried casting number 3919842. This head was used in PRODUCTION for 1968 and 1969 Corvettes and Camaros with the L-89 aluminum head option option (for L-71 and L-78). This head was discontinued in March, 1996.In Appreciation of John HinckleyComment
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Re: Correction
Joe - I believe the difference is the 076 has the vane in the D port on the exhaust side, wheresas the 6074 did not. I have a set of the 076's on my crate LS6 someday destined for my 74 temporary LS6 conversion/driving engine. I didn't realize the inserts were not hardened, and had all the work on the heads done with these seats in place thinking they were. Hopefully they will be fine running premium unleaded, and the steel they use while not hardened will be durable for normal street use with the occasional heavy foot treatmemt......CraigComment
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Re: Correction
Craig-----
The "vanes" were part of the exhaust port configuration differences that I was previously referring to. The other part is the fact that the '074' heads have exhaust ports which are "round" whereas the '077' head has the "D-shaped" configuration.In Appreciation of John HinckleyComment
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Re: Correction
Thx Joe - wasn't there a D port verions aluminum head without the vane too? Seems like I saw a set at the local speed shop once, and I didn't think it was the common cut the vane out approach.
Should I worry at all about the durability of the steel inserts since they are not hardened? My guess is no, but just curious. I am not in the financial mood to have the head work redone at this point Thx, CraigComment
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Re: Hardened Valve Seats
General question.....I have a BB 67 that was restored by Nabers motors in 1990. Engine work was done , but I have no idea if hardened valve seats were used back then. Car has been driven about 400 miles per year since restoration using premium unleaded fuel only. Is this going to harm the engine in any way, or should I be using a lead additive? Haven't had any problems so far..just curious. ThanksComment
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Re: Hardened Valve Seats
Chris - I would not worry, and if it doesn't ping, then I would certainly not add gas suppliments. If it does, I would back the timing off and unless it takes too much to fix the ping, additives would not be of help. If it does, then consider high ocatane fuel from Union 76 ....it may be available locally like it is here in Tucson......CraigComment
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Re: Correction
Craig-----
There are several GMPP heads, including the current generation, which feature "D" ports without "vanes". I wouldn't be concerned about the valve seats in the '077' heads. They'll likely last as long as you're ever going to need them.In Appreciation of John HinckleyComment
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Re: Hardened Valve Seats
THanks CraigComment
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Re: Hardened Valve Seats
Chris, the story my machinist gave me in 1983 when putting a 427 back together, if you could get 100,000 miles before a valve job with the leaded gas, then you need to figure a valve job at 75-80,000 miles with unleaded gas on a big block. That was based on his experience with machining heads.
You planning to do 75,000 miles, 400 miles a year?
The machinist on my race crew said in his shop, they had more damage from hardened seat inserts dropping out or being installed wrong than they had from recession due to no lead. He also agreed that in the big picture, there was little difference in actual driving.
Drive it, don't worry about it.Comment
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Re: Correction
Thx Joe!Comment
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