Help me out here...still learning.

What does the term "hardened valve seats" refer to and what year did it change ?

Was this a change in 75 due to unleaded gas ?

Leading to....While I re-cam my 74 Big Block with a Comp Extreme Energy 268 H.......IF I replace the valves, while I'm there....What do I need to be sure to do?

Thanks for any advice or discussion................

 

If you have been told to have hardened valve seats because of the gas, don't.

The recession is greatly exaggerated.

A friend running a machine shop told me once that his take was that if you got 100,000 miles before a valve job with the old head and leaded gas, you'd probably need a valve job around 80,000 or so with unleaded, based on the heads he had worked on. If a big block, don't bother at all, there is no difference.

You planning on putting 80,000 miles on your car?

Another friend running a machine shop a few years ago in South Florida said the big thing with hardened inserts was that many are done wrong and drop out. When they do, they really mess things up depending on the engine speed.

Feel like trashing your heads?

 

PR is pretty much on the mark ... I wouldn't sweat non-hardened seats unless I was routinely towing long haul.

AFAIK ... hardened seats appeared in MY1971 in preparation for the unleaded fuels which were known to be soon mandated.

I recently sold a brand new NOS & NIB set of bare iron bowtie heads ... by the heat-blueing around the exhaust seats ... you could see where they were induction-hardened. Quite similar to how some of the better crank makers harden journals.

 

I think you have learned all thats necessary on the subject. All the advice is correct, dont worry about it until it becomes necessary. Some of our reconditioned heads do require net guides and seats but as stated, when necessary {from old age}

 

Here's the deal and story on hardened seats....

When the auto industry realized that there would be a switch to unleaded fuels in 1975, there was some concern about valve seat erosion and recession due to the removal of lead from the fuel. The lead was seen as a valve seat lubricator, of sorts. The reason for the concern by the automakers was that the automakers have to be concerned about every possible operating condition of the engine, including gross owner abuse: If sombody buys a 350 2-barrel Malibu station wagon with the trailer towing option on it, you have to assume that they will hitch a 6000-pound horsetrailer behind it and run it at wide open throttle (WOT) up the Continental Divide for 2 hours straight. And GM better not get a warranty claim out of the deal... So the valve seats have to be able to handle extended exposure to extreme exhaust gas temperatures due from insane operating conditions like this.

Starting in 1971, GM started doing an induction hardening process on on their valve seats for this reason.

In the late 70s, the SAE did a bunch of testing on valve seats and seat erosion due to unleaded gas (I know this, because I've been a member of the SAE since the mid-70s). Here is what they found:

Vehicles operated for extended periods of time at WOT (like pulling a horsetrailer up the mountain for 2 hours with the pedal to the metal) can see some seat erosion and valve recession due to the elevated exhaust gas temps. Vehicles operated in such conditions (trucks and towing vehciles) benefit from the hardened seats.

In all other cases, providing valve seat pressures are equal to or less than 110 pounds, there is no valve seat erosion or valve recession when the engine is operated on unleaded fuel, including if the vehcile is operated occasionally at WOT (like drag racing). In fact, the SAE found that the installation of aftermarket hardened seats was normally a much bigger threat to the longevity of the engine than the use of the stock non-hardened heads, since the aftermarket pressed-in seats had a tendency of falling out under very high exhaust gas temperatures (which is when you need them). This would result in the complete destruction of the engine.

In your case, you should not consider a change at all: Your 1974 heads have induction hardened seats in them.

 

While I agree with most of what you have said here, there are two points I would make here. One on a performance engine you will most likely want more than (110#) on the seat with the cams most run. Secondly if you run "Rotator" on the exhaust as most chevy engines have, you will most likely have the valve gring it self into the port. Seen this a lot in trucks and to a lesser amount in cars. Bottom line, get rid of the rotators if you haven't already, and if you run a fair amount of seat presure get good one piece valve and have a shop that knows what they are doing install the hard seats. They will stay put if done right. Manuel

 

This is for non-hardened seats. From '71 up, the small block heads had them. The big blocks were hardened from before, due to the much higher valve seat pressures and since the intended use was towing, heavy loads, and racing.

For his '74 big block heads, DO NOT have them install seat inserts unles sthe head is screwed up. You do not need them.

And regardless, most shops will say they are experts at putting them in. See if they will back it up with a $10,000 guarantee if one drops out and destroys your original motor and devalues your original Corvette.

Bet they won't.

 

Just wondering...how many here have had replacment seat inserts fall out?

 

Thanks everyone....good stuff....good advice!



Fred ...

 

check out the xe 262 h.........i have the xe268 and i like it but it was pointed out to me that the 262 had better or equal performance look a the dyno tests on the Comp website

 

Good quistion. FYI, All Aluminum heads have hard seats in them as well as most all later model factory iron heads also. "World" big blocks heads are this way now also as well as the factory late 502's and up. Manuel

 

Thats my point... It seams that some have obviously had problems with valve seat inserts falling out. But thats it. You only hear about the ones that go bad. You dont hear about the thousands that have stayed in without a minutes problem, or the satisfied customer thats happy with the good job he received.

 

I wouldn't install hardened seats on early heads. Some of these castings can be thin which contributes to cracking between the seats.
If you need to have the seats freshened up, just run 25% leaded for the first 1,000 miles. Cast iron work hardened very quickly and as already stated stick with the stock spring rate of 80 pounds. Even the LT-1 motor that will buzz to 7,000 RPMs used the 80 pound springs found in almost every 350 out there.

 

The only thin casting 350's I have seen are from 1978-1981 462624
If the heads are early enough casting & are not flamed hardend & in need of some valve work. put the hard seats in. Once thats done, you wont be having to put fuel additives in eveytime you fill up.

 

How far does the factory hardening extend out from the stock valve seat? I'm thinking that you might need the inserts if you're going to larger valves.

 

Yes, if it is a street application.

 

A friend was stranded in the middle of France when a seat fell out. But a heck of a lot of other people I know have had hardened seats installed & have had no problems. One good thing is that a head that's seen plenty of abuse from animals with valve seat cutters (badly pocketed valves) can be brought back to as good as new when hardenend seats are installed. Unless the seats are badly pocketed, or damaged, I wouldn't bother getting hardenend ones installed. None of the people with hardened valve seats have noticed any valve seat recession, but nor have those of us who ignored all the myths, hype & panic & are still running the original seats.