Hardened seat ? [Archive] - Chevy Nova Forum

: Hardened seat ?


taz3
5th-December-2010, 05:49 PM
What year would they have started for sure? I'm going to assume it will be cheaper to rebuild a set of heads with the harder seats already installed, rather than having this added to the rebuild process.

patman
5th-December-2010, 05:54 PM
IMO...if you're not using it for a DD and racking up 15Kmiles/year on it, you won't notice the difference.

stock z/28
5th-December-2010, 06:49 PM
To the best of my knowledge, 1971 was the first year for induction hardened ex seats.

I usually look at ex temp and load on the engine in regard to my concern about ex seat recession. If its a light weight low load vehice, I usually dont worry much about it. A truck towing a trailer is a lot more in need of some ex valve/seat help.

If its a real issue, I much prefer an insert over the induction seat, but they do worry me in some ways, and I just about wont put a seat in a small block with a 1.6 ex valve.

nova_me1970
5th-December-2010, 10:31 PM
I believe it to be 71' also. 1'st year for lower compression and unleaded gas.

Paul Wright
6th-December-2010, 11:07 AM
Actually, 1971 was first year for low lead gas. Catalytic converters didn't come out until 1975 that required no lead.

SBC's have integral valve seats. Meaning it's part of the casting. They would induction harden the seat area with electric induction heaters sort of like a spot welder. If the seat has been ground several times, the hardness layer may not be there anymore, or substantially reduced.
Installing new seats means machining it out and pressing in a seat ring. These are the same/similar as they use on an aluminum head.
The same is true for guides. SBC uses integral guides. When they wear, this effects the centering of the valve and consequently the seat contact patch.
To properly make a head marginally equivalent to a new head you need to install new guides and seats. With the advent of the Street Replacement head this isn't cost effective. I have all the equipment to re-do heads and it's cheaper and easier for me to buy new, and better castings.
The only time I would go to that kind of trouble is if there is some rule requiring old castings. Even with casting rules, you'll see bogus camel humps with authentic looking casting marks. Money (and cleverness) can buy your way around any rule book.

stock z/28
6th-December-2010, 12:02 PM
Hi Paul,

In regard to the depth of the induction hardening, the real input I can give is that in machining the castings (including 1971 487 castings) from a 1.5 ex valve to a 1.6 valve the hardness depth is pretty apparent on the fresh cut material and it would take a lot of valve jobs (in my opinion) to get to "soft" material.

I will say there would appear to be a lot of variation in depth and especially actual achieved hardness in various castings.

In actual "racing" situations I have had "0" issues with valve recession over the years, and I may be stupid but I would personally prefer a "normal" (non-induction hardened ex seat) to a lot of heads with the ex seats modified.


AS far as the better castings goes, undoubtedly the age and usage of stock heads has taken its toll on original castings, and a new aftermarket head is usually a better value, but in a lot of applications if I had my choice between a "new" GM casting and comparable aftermarket version, I think I would prefer the GM. I have seen a lot of issues with aftermarket replacement heads. In my opinion they (the aftermarket) does not even come close to GMs quality control or concern (look at the Milidon oil pump issue).

I guess if an aftermarket part offers a real performance and/or durability advantage over an OE part, its no brainer, but I am really tired of most aftermarket suppliers lack of responsibility after the sale.

nova_me1970
7th-December-2010, 09:04 PM
Sorry Paul, but I disagree..... The Shell gas station I worked at in 71' had three pumps, Reg, Premium, and Unleaded. I remember a tag on the unleaded pump stating, Contains No Tetra-eythal lead. Maybe it was differant in the U.S...... Not sure.:yes:

Paul Wright
7th-December-2010, 09:23 PM
Straight from the EPA (USA) web site (http://www.epa.gov/history/topics/lead/03.htm):

Lead has been blended with gasoline, primarily to boost octane levels, since the early 1920s. EPA began working to reduce lead emissions soon after its inception, issuing the first reduction standards in 1973, which called for a gradual phasedown of lead to one tenth of a gram per gallon by 1986. The average lead content in gasoline in 1973 was 2-3 grams per gallon or about 200,000 tons of lead a year. In 1975, passenger cars and light trucks were manufactured with a more elaborate emission control system which included a catalytic converter that required lead-free fuel.

However, Amoco did make and sell a lead free gasoline prior to it being required by law. The OP question is when did Chevy heads change to hardened seats due to mandatory no-lead gasoline.
I haven't found definitive information as to the exact year, but they went to the light weight head in 1974 and the 1975 head had the 7th exhaust bolt hole. Because the 74-85 heads are crappy flowing, I don't see much benefit to selecting them just for hardened seats.
A 1971-1973 head may have hardened seats (Jeff will know), but the age and rarity might make them hard to find in good shape and right features.

I don't disagree with what Jeff said, but I still think that the aftermarket castings are a better starting point. I don't use them out of the box because of the QC often isn't to my standards, but I prefer to fit them out myself anyway. Much better than trying to resurrect old boat anchor heads.

stock z/28
7th-December-2010, 09:48 PM
Straight from the EPA (USA) web site (http://www.epa.gov/history/topics/lead/03.htm):



However, Amoco did make and sell a lead free gasoline prior to it being required by law. The OP question is when did Chevy heads have hardened seats due to no-lead gasoline.
I haven't found definitive information as to the exact year, but they went to the light weight head in 1974 and the 1975 head had the 7th exhaust bolt hole. Because the 74-85 heads are crappy flowing, I don't see much benefit to selecting them just for hardened seats.
A 1971-1973 head may have hardened seats (Jeff will know), but the age and rarity might make them hard to find in good shape and right features.

Paul, in my opinion the hardened seats and in some cases different valves was not solely based on lead content levels.

I think in 71 GM comp ratios dropped and a several other emission control devices were added. I think increased ex temp became a concern.

I remember that I had just started working for a Buick dealer and starting in 71 the seats were induction hardened and the valves were Aluminized and were not to be refaced. You could grind the seats but not the valves.

I can show you a 71 head with hardened seats (induction and the casting is 487).


I know the first HEIs I saw were in 74 and that was to fire a very lean mixture, I guess.

Paul Wright
7th-December-2010, 10:42 PM
Again, I don't disagree. As in my earlier post, I thought 1971 was the first year for hardened exhaust seats because of the mandate for low lead fuel (with corresponding low compression). If you've seen intakes hardened as well, I won't disagree, but certainly by 1975 both seats should be hardened, but the heads weren't of performance value.
1970 and earlier are usually (in my experience) not hardened. That leaves the 1971to 1973 heads as the only ones that might work, if he needs OEM hardened seats in a heavy weight casting.

stock z/28
8th-December-2010, 12:00 AM
Again, I don't disagree. As in my earlier post, I thought 1971 was the first year for hardened exhaust seats because of the mandate for low lead fuel (with corresponding low compression). If you've seen intakes hardened as well, I won't disagree, but certainly by 1975 both seats should be hardened, but the heads weren't of performance value.
1970 and earlier are usually (in my experience) not hardened. That leaves the 1971to 1973 heads as the only ones that might work, if he needs OEM hardened seats in a heavy weight casting.

Hi Paul,

I don't know that I have seen any hardened intake seats on a cast iron head, regardless of year?

I am basically going from machining them but the intakes always appeared as normal cast, non-hardened.