Hardened valve seats - do they really matter?

-
Princess Valiant

Princess Valiant

A.K.A. Rainy Day Auto
FABO Gold Member
Joined
Dec 14, 2011
Messages
26,317
Reaction score
23,591
Location
Colorado
So i am about to invest a couple hundred bucks and mill a slant six head .100

However I remember in auto school being told that the 73 and up heads have hardened valve seats to run better on the then new unleaded fuel.

I can say I have never run a lead additive on the 73 and older heads and I've never had any issues.

Before I put money into machine work on a head like that, should I try to find a 73 or later head to mill, or just mill my 68 head and don't worry about it?
 
You'll know when you take your head off, by how far the valves have pounded themselves into the seats. It takes thousands upon thousands of miles to get to be like that.
If it has mechanical lifters, you might notice it, by more often lash adjustments.
My opinion is that if yur gonna put 12,000 miles a year on it, ok, get hardened seats.
But if just an occasional cruiser , then I wouldn't bother. The car will rust out before it needs a valve job.
But
if the head needs a valve job now, there is no better time to install hard seats.
Plus, I know that you're always on a budget, so, it's cheap enough to do a valve job 6>10 years into the future.
But
you'll know by looking at the installed valves, if it needs to be done, and once the valves are out, it will be obvious.

Oh and BTW, hardened seats will not make it run better of themselves. Just a lot longer at the same good, lol.
But, .100 of the head is a heckuva thing.
If my math is right, that will take an 8/1 225slanty to 9.5Scr. With a stock cam, the pressure is predicted to rise from 140@sealvel, to 175 with a stock cam. I imagine and hope, that you're gonna cam it up to drop the pressure down into pump-gas territory.
 
Last edited:
In a light car like an A body that will haul around only human loads, IMO, they aren't necessary. If you were talking about even a shop truck, I would say yeah. Even a crappy old shop truck hauls or pulls something every now and then. Exhaust temperature is what it's all about. In a light car that's only used for transportation, exhaust temperatures are low and the need for hardened seats is just not there.
 
For a carbureted light duty engine I wouldn’t worry. They seem to have problems most on lean running engines that are heavily used.

When I was sourcing magnum heads, I found that most of those motors have trashed exhaust valve seats. Now they are “hardened,” but they (like those from the 70s) aren’t like the stainless or stellite valve seats that a machine shop would install, rather, they are just sligntly hardened steel. If you want seats for a lifetime, spend the dough. But otherwise it’ll be alright
 
remytherat said:
For a carbureted light duty engine I wouldn’t worry. They seem to have problems most on lean running engines that are heavily used.

When I was sourcing magnum heads, I found that most of those motors have trashed exhaust valve seats. Now they are “hardened,” but they (like those from the 70s) aren’t like the stainless or stellite valve seats that a machine shop would install, rather, they are just sligntly hardened steel. If you want seats for a lifetime, spend the dough. But otherwise it’ll be alright
Click to expand...
Tungsten Carbide is most of what they use now and it ain't cheap. lol
 
My machinist told me years ago that the valve seats were induction hardened and that the hardness only went a few thousandths deep into the metal. A basic valve job would cut through that quickly. He always recommended the installation of hardened seats for exhaust valves only.
 
1729502004857.jpeg


400 in a 78 Dodge D100. Less than 200 k miles. Truck was NOT worked hard often.
 
I have had the exhaust valves done but i had bigger valves fitted at the same time, the shop seemed very keen to relive me of my money and at the time i was not in a position to argue the toss.


if you fit stainless valves, the chances of them micro welding repeatedly to the seats in a cast iron head are greatly reduced

its the micro welding together due to heat in the seat and spring pressure, then pulling away at the surface of the seat as they open that causes the recession.
what is pulled away is burnt off the valve and the process repeats.

like crazy gluing you thumb to your finger. pull em apart and one is the winner and one is the looser when it comes to the top surface of skin....

if you can avoid that microweld due to a good choice of valve material the action of the valve hitting the seat does a very good job of work hardening the the seat anyway further reducing the possibility.

originally the valve head and the valve seat were made of materials that were too alike, and they needed leaded petrol or alternative additives to avoid this microwelding.

id spend my money on new guides, cut for modern seals, narrower stem valves, or headers and a cam.

Dave
 
Hardened seats if you want it to last forever or you use it under harsh conditions. Otherwise, if you just grind the valves, you won't put enough miles on your old car for it to be an issue.
 
From what I’ve read over the years, it depends. Light car, light load, good fuel/air mix and good cooling system, it would be fine for a long, long time. Heavily loaded truck running lean, bad timing and/or cooling system, it could look like the pic above. If I was planning on driving cross country, I’d do hardened seats.
 
I will tell you what the machine shop guy told me when I sent some J heads in. He said "if you are daily driving it yes install the seats if you are car show cruising it they should last as long as you cruise the car" the as long as may be a reference to my age I'm in my 50s...Im not arguing whether the guy is right or wrong but I agreed and didnt have the seats installed. . A car show cruiser for me may see 1500 miles a year, and Ill throw the lead additive top cylinder additive in for good measure...also doing everything 100% just makes it better for the next guy who low balls you at sale time I like to leave some of the fun for them...:)
 
People don't realize what the main cause is for sunken valves due to beat out seats. It's running a dirty air filter for extended periods. The dirt, dust and grit grinds exhaust seats to pieces. Valve seat recession. Dust and dirt in the incoming air fuel mixture is the #1 cause. What do you think a machinist is going to tell you? That's like asking a hooker if you need her for a night.
 
Ok. This is all some good info.

A lot to digest. Now that I have a visual of what a valve seat failure looks like, my 68 slant head is definitely a good head. So I think I'll just mill it and use it.

Milling a head these days is a couple hundred bucks so I just wanted to be sure.

I do plan to daily drive the car but if it's made it this far, 56 years later, surely it will take more than me to kill it.
 
Princess Valiant said:
Ok. This is all some good info.

A lot to digest. Now that I have a visual of what a valve seat failure looks like, my 68 slant head is definitely a good head. So I think I'll just mill it and use it.

Milling a head these days is a couple hundred bucks so I just wanted to be sure.

I do plan to daily drive the car but if it's made it this far, 56 years later, surely it will take more than me to kill it.
Click to expand...
If the seats look good, I would lap the valves in. That way, you'll still be using the induction hardened seats and you'll assure a good seal.
 
I think it comes down to what you want to spend. I had 2 sets of J heads and i think I mentioned this in another thread but, I sent the 1.88 set out in 2013 it cost high 400 and some change may as well say $500 dollars because I think it was 496 or something plus add the cost of the cores. Cant sell em for that, then this year I sent a 2.02 set of js out and that set needed more so it was high $600 and some change may as well say $700. I'm definitely not breaking even on that set but. They are good to go on an engine that will be low mileage cruised. Id take the chance ifand did to save some money also Id run some lead additive top cylinder lubricant etc. Maybe not every fill up but every other month or so. I think if it is a 70s truck or van id put the seats in but a 70s truck or van should already have them no?
 
I had an owner of a '71 440HP tell me that for his use, hardened seats weren't warranted. He doesn't run it hard at all, mostly driving to/from swap meets. Imagine his surprise when he finally cracked open the engine to find all eight exhaust valves recessed nearly .100" into the heads. If the head's off, I'm putting hardened seats in it regardless.
 
NoCar340 said:
I had an owner of a '71 440HP tell me that for his use, hardened seats weren't warranted. He doesn't run it hard at all, mostly driving to/from swap meets. Imagine his surprise when he finally cracked open the engine to find all eight exhaust valves recessed nearly .100" into the heads. If the head's off, I'm putting hardened seats in it regardless.
Click to expand...
Well aren't you special...:lol:
 
Princess Valiant said:
So i am about to invest a couple hundred bucks and mill a slant six head .100

However I remember in auto school being told that the 73 and up heads have hardened valve seats to run better on the then new unleaded fuel.

I can say I have never run a lead additive on the 73 and older heads and I've never had any issues.

Before I put money into machine work on a head like that, should I try to find a 73 or later head to mill, or just mill my 68 head and don't worry about it?
Click to expand...
For me it would be determined if you were having a valve job done. If so, then I would install them, they are already machining. I you just planned to lap them, then I wouldn't worry about it. Paying for milling - Don't you have a mill? C'mon girl. You have high temps and elevation by you, make sure you are running rich enough.
 
I asked the local small time machine shop about milling me some slant heads .1 He quickly said NO WAY!!!! Guess he did not want to wear out his machine!!
 
You must log in or register to reply here.
-

Back
Top