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After being chastised every time I post that you should have hardened seats installed when you are rebuilding your heads or engine Notnuts16 has inadvertently posted pics of the seats receding on his Corvette. Now you can look at the pics and say oh that's not going to happen to me I have a Corvette and the way we drive them they are not necessary, bull. Looking at the photos you'll notice the far left exhaust seat is receding on the 461 and both of the center exhausts on the 462. This is common as this area of the head is the hottest. I don't care which one of the most learned members come on here and say they aren't necessary, they haven't installed or heat treated every single exhaust seat since 1973 for no reason. I can hardly wait for this.
I've cut into water before myself. Then I learned quickly to use as small and shallow of a seat as possible. And never attempt to put hard seats in an early 1.600 head. They weren't designed for big valves and were installed as an after thought. So the area under the seats is just too thin to attempt it as well as being too thin at the larger intake valve and cracking there from press fit. But in a normal 1.94/ 1.500 head there is no way I wouldn't install them.
I've cut into water before myself. Then I learned quickly to use as small and shallow of a seat as possible. And never attempt to put hard seats in an early 1.600 head. They weren't designed for big valves and were installed as an after thought. So the area under the seats is just too thin to attempt it as well as being too thin at the larger intake valve and cracking there from press fit. But in a normal 1.94/ 1.500 head there is no way I wouldn't install them.
It was a pair of 1.94/1.50 heads which I managed to turn into door stops.
I have put nearly 100,000 miles on my 66 since 1986 and car has a total of 172,000
No valve issues whatsoever.
At this point if a valve problem occurs I dont think I could attribute it to no lead.
Anecdotal evidence. You will hear some supporting both sides of this debate. Good luck whatever route you choose.
Don't install the hardened seats and maybe you will get valve recession. I haven't experienced it but I'm not going to say it's impossible.
Commit to installing the hard seats and, if you go into the water jacket, you've just made pretty doorstops. I have experienced this.
So, pick your poison.
I agree with you too. After weighing options and risk, I bought a new set of Trick Flow heads that have hardened seats. Plan on selling the original heads to recoup some of the expense. Considering rebuild cost, sales price and etc, I won’t have anymore invested in the new heads than I would have had in the old ones.
Personally I don't think hardened seats are needed for normally driven collector car engines. We have been forced to use lead free fuel since the early 70's and of the dozen or so engines I've dealt with in that time I haven't run across one with receded exhaust valve seats. If you're beating on your car a lot, probably should get the exhaust valves done if anything for peace of mind.
My most recent job, a 68 Cadillac 472 has excellent seats with its factory 10.25 compression. Aside from stem seals, I'll be cleaning them up and bolting them back on as is
I have put nearly 100,000 miles on my 66 since 1986 and car has a total of 172,000
No valve issues whatsoever.
At this point if a valve problem occurs I dont think I could attribute it to no lead.
Anecdotal evidence. You will hear some supporting both sides of this debate. Good luck whatever route you choose.
Installing exhaust inserts doesn't require any "magic", just a little extra precaution, haven't hit water on ANY seat install for as far back as I can recall!
On the "top" side of these early heads you have a very similar issue when machining the early castings to accept dual valve springs, just takes a bit more care.
Way back when, we had "special" seats made up by Martin-Wells strictly for this platform. Worked so well we began machining our own inserts using a radius cutter on our lathe in-house!
(Add) Even many of the old Flathead Fords had inserts from the assembly line, not all, but many did!
Thanks, Gary in N.Y.
P.S. Here's a shot of the inserts along with the "blade" for doing the .094". The inserts on the left are "as-is", the ones on the right are the finished pieces! have NEVER hit water using these inserts. We also use an adjustable seat cutter kit to guarantee the correct press-fit.
radii on the inserts!
Last edited by GOSFAST; 09-11-2018 at 10:52 AM.
Reason: Add info
There are several other factors that can create recessed exhaust valve seats other than “aggressive driving”. Retarded timing curve, lean mixture, and valve lift/duration are three. Anything that introduces additional heat into the exhaust. Simply saying “I’ve never had issues.” is an incomplete assessment. I recommend hardened seats on any head that can handle them when they are being rebuilt, period. But then, I drive these cars the way they were meant to be driven - often and with spirit!
How does the installation of "hardened seats" prevent the seats themselves from recessing into the head? Or, are you saying that the VALVES recess into non-hardened seats? Trying to understand the basis for the "debate"....
Mine were sunk/receded pretty bad, daily driven up til late 80s. Ran fine but didnt when it came time for a valve job they needed replacing.
I put larger valves with hardened seats, you bet. (462 heads)
Don't install the hardened seats and maybe you will get valve recession. I haven't experienced it but I'm not going to say it's impossible.
Commit to installing the hard seats and, if you go into the water jacket, you've just made pretty doorstops. I have experienced this.
So, pick your poison.
I also made a really expensive trot line weight out of a 461X head. Leaked water out of the end exhaust seat. I will never screw with old iron camel hump heads again. Aluminum heads will be on any engine I build from now on.
After being chastised every time I post that you should have hardened seats installed when you are rebuilding your heads or engine Notnuts16 has inadvertently posted pics of the seats receding on his Corvette. Now you can look at the pics and say oh that's not going to happen to me I have a Corvette and the way we drive them they are not necessary, bull. Looking at the photos you'll notice the far left exhaust seat is receding on the 461 and both of the center exhausts on the 462. This is common as this area of the head is the hottest. I don't care which one of the most learned members come on here and say they aren't necessary, they haven't installed or heat treated every single exhaust seat since 1973 for no reason. I can hardly wait for this.
You can't draw a broad conclusion from one data point. Further, we have zero information on the service life/maintenance history of this engine other than a head was replaced. Was it a used head installed as is, or rebuilt? How many miles? How hard was the use? Did the engine receive proper maintenance?
In addition to penetrating the water jacket, there have been reports or seat inserts dislodging.
As mentioned, the typical retarded spark advance map of OE engines, especially emission-controlled raises EGT, which contributes to seat recession.
I am also concerned about the loose OE clearance recommendations for OE mechanical lifter cams. That's why I analyzed all the lobe data from the GM drawings and used the actual rocker ratio at low lift (1.37:1) to calculate clearances that will ensure that the valve is seated at no more than clearance ramp velocity under all operating conditions. The looser OE recommendations seat the valves at higher velocity, which will contribute to seat recession.
From what I've read over the years, the anecdotal evidence, which is all we have, that normal road use will not result is excess valve seat recession vastly outweighs the evidence that seat inserts are of any value, and the potential problems associated with installing seat inserts far outweighs the potential benefits
How does the installation of "hardened seats" prevent the seats themselves from recessing into the head? Or, are you saying that the VALVES recess into non-hardened seats? Trying to understand the basis for the "debate"....
Ductile iron stock heads are relatively soft and the seats are simply machined into the head material. Hot exhaust gases can cause the exhaust valve seats to overheat to the point of plasticity. The valve spring can then pull the valve deeper into the seat causing this issue. Hardened seats made of a harder material are pressed into machined pockets in stock heads and aftermarket aluminum heads to fix the issue. Used in conjunction with stainless steel valves prevents this recession.
Vintage Corvette heads are gray iron, not ductile iron, and gray iron is a very hard and tough material, which is why seat inserts were never installed.
The thin coating of lead oxide on valve seats, which seems to provide protection from recession is established early in the engine's life and is very long lived, so if you're concerned about seat recession, use leaded fuel early in the life of the engine and add some leaded fuel every few thousand miles.
When I had the engine rebuilt and heads enlarged for 2.02/1.60 valves, pocket ported, and port matched, I had Flow Technology (the infamous Juan Mendoza) put in the hardened seats. This had to be 30+ years ago and I've never had any problems. I even threw the belt and overheated the engine once with no ill effects. (Try that with aluminum heads.)
09-11-2018, 08:54 AM
We don't need hardened seats!
