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Cylinder Heads

3K views 7 replies 7 participants last post by  Ossie 
#1 ·
In 1976 or 1977, GM began to induction harden valve seats because lead was no longer in pump gasoline. I've heard and read conflicting information about running earlier heads on street engines. Some say it's no problem; some say you have to use an additive; and some say don't do it.
Any thoughts and/or experiences?
 
#2 ·
Experience? Yes. I used to run a set of 041 castings and they had stock seats. I ran lead additive which was said to prevent the seats from being pounded away, well, it didn't. Over the years I put a ton of money into those heads, when I took them off that last time and seen they needed seats I sold them to some roundy round racer.
 
#4 ·
Ossie said:
In 1976 or 1977, GM began to induction harden valve seats because lead was no longer in pump gasoline. I've heard and read conflicting information about running earlier heads on street engines. Some say it's no problem; some say you have to use an additive; and some say don't do it.
Any thoughts and/or experiences?
There is quite a bit of inconsistency with exhaust seat recession on older heads run without additives.This probably tells more about inconsistent metallurgy at the foundry with different batches of iron than anything else. There are probably those few days when higher alloy blocks were the casting work order of the day and when that job was finished and the next job was a run of heads, they probably at least started the run with all or some lesser mix from the preceding block casting session. I this case you ended up with better wearing heads than is normally cast.

Old heads can have hard seat inserts installed, this isn't too expensive. It is a process used in service to repair other wise good heads that had a damaged seat. It is also used by the factory on heavy duty heads including the recent Vortec and was applied to engines going into non-gasoline as fuel use such as propane or natural gas. So this is a common process.

Putting in hard seats or casting with high nickel alloy iron is too expensive for normal production so the foundry's started using induction hardening which is to use a powerful oscillating magnetic field to heat the seat area to a red hot temp and then suddenly chilling the zone making for a very hard seat. Fast and cheap something Detroit adores.

Bogie
 
#5 ·
It was 1975 that catalytic converters and unleaded gas came into use. Over the years I've read so many conflicting articles on unleaded gas. I read one by the military that said they found no ill effects from unleaded gas. I've read also it has to do with the cast iron formulation. Some companies use a softer formulation like Chevy and others such as AMC used very high nickel content and had very hard cast iron. Before unleaded gas, burn valves and valve jobs were very common. The only reason lead was ever put into gas was to turn cheap low octane gas into cheap high octane gas. At one point there was no lead in gas. I can't say for sure but I read it was Kettering from GM who discovered putting lead into gas for the WWII aircraft to make high octane gas. On the plus side for unleaded gas is that cylinder bore wear is substantially reduced according to articles I've read in the past.

Best thing to do is to google the topic and make your own opinion.
 
#6 ·
Okay,. I'm gonna muddy it "up" even more. Chevy heads, '73. Other GM makes, '72... It wasn't "about" unleaded fuel or catalysts. It was about EGR (Exhaust Gas recirculation, used to inject spent gasses into the idle mixture to "lean" it to reduce oxides of nitrogen) and the radically higher exhaust temperatures accompanying it. federal mandates had '72 "scheduled" for use of EGR in American vehicles. Chrysler wasn't "ready", so they petitioned and won a "stay" until '73. At least Pontiac, Cadilac and Bucik (can't say about Olds) had inductoin-hardened seats in '72 castings, "just in case".

It's very common today to enlarge the seats in SBC heads for 2.02 or 2.05" intake valves and 1.6" exhaust valves. When doing this, the seat can be "reprofiled" to have a weider area to dissapate the heat, effectively making the "hard" seat unnecessary. However, if staying with the standard valve sizes and there's ANY "sign" of previous damage, hard seats are called for (exhaust side ONLY). If you make the 45 eg seat .090-.100" wide, and don't "lug", retard timing or lean it out, it will be fine, unleaded gas and all...

Jim
 
#7 ·
On passenger car heads w/o hardened seats (including heads w/1.6" replacement valves installed) I have seen more wear on seats from worn guides than from unleaded gas. I have seen truck heads w/rotators that the exhaust seats were so recessed the valve tension was probably less than 50#. I could open an exhaust valve w/a rag and my thumb! This is just my observation and isn't based on anything scientific.
 
#8 ·
Sbc Cylinder Heads

Thanks for the replies. I hadn't thought about the EGR possibility. My machine shop guy enlightened my to the water passage changes Chevrolet has used over the years which may allow more heat to build in the area of the two, center valves.
I've never had a cracked head problem (other than the one on my shoulders) unitl I disassemebled a 1978 350. All four of the center exhaust vale seats were cracked into the combustion chamber. Tis is why I'm trying to figure out which heads to purchase,.
 
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