Hardened Valve Seats or Not?

-
!340cuda!

!340cuda!

Well-Known Member
Joined
Apr 3, 2015
Messages
113
Reaction score
29
Location
kansas
Built my 340 25 years ago and have not been able to finish build until now. Problem is that back then I had heads rebuilt but failed to have hardened valve seats installed. Now I am going to finish car and need to decide if hardened seats are important enough to pull heads off and have done.

I plan to drive car around town, to local and distant shows. I don't plan to push the car too hard, but will punch it from time to time.

Should I do the hardened seats, use a lead additive with unleaded fuel or are there other options to consider?

Thanks for your thoughts.......
 
IMO, in a LIGHT street car like an A body, they are not needed. If you were putting the engine in say a truck to haul heavy loads, I would say do it. That's my opinion. I am sure others will vary.
 
In the short term you will be fine. In the long run you will beat the exhaust seats out of it and will have to pull the heads off and have them done. I would say if you have the funds and time , do it now.
 
I ran a unmodified '70 383 Road Runner for 50K (or more) miles exclusively on Amoco Super-Premium no-lead gas back in the '70s and the guy that bought it from insisted upon doing a compression test before he bought it. As I recall it was nearly perfect. This was a daily driver, never modified and never really beat on. So it all depends... There were a lot of cars running on Amoco Amoco Super-Premium no-lead back then.
 
69_340_GTS said:
I ran a unmodified '70 383 Road Runner for 50K (or more) miles exclusively on Amoco Super-Premium no-lead gas back in the '70s and the guy that bought it from insisted upon doing a compression test before he bought it. As I recall it was nearly perfect. This was a daily driver, never modified and never really beat on. So it all depends... There were a lot of cars running on Amoco Amoco Super-Premium no-lead back then.
Click to expand...

Do the math you spent over $2500.00 over 87 octane during that 50,000 miles. Cheaper and the correct way for the OP to have the harden seats added now.
 
How about thoughts on using a lead additive. Does it make any sense to use it?
 
Hi,

Back in the mid 70's when they started to reduce lead content and when it finally went away my 71 Charger 383 lost 3 exhaust valves after several 6 hour highway trips. Fortunately, B block engines were still in production in the late 70's and I was able to swap on a set of later heads with hardened seats.

The valve seats in these engines were only surface induction hardened and depended on the lead for lubrication and heat transfer from the valve surface. I have to agree with SGBARRACUDA it's only a matter of time before the valves burn. If it were mine I would do the hardened seats now. I had hardened seats installed on my 69 Barracuda 318 when the heads were redone.

By the way, I pretty sure that old time Amoco unleaded was loaded with phosphorus which did the same things as lead in terms of the valves.
 
I have come across many articles over the years, that insisted that the 71-up heads had the hardened seats. I cant speak to the truth about it.
It "seems to me" that if you had 71 heads,and with youre limited useage, it would be a non-issue for many years to come.
With pre 71 heads? Hmmmmm. I think I would patiently look for and freshen up a set of later heads, or magnums, and put them on the shelf, at the ready. See how many years the current heads go, and then report back.
Kansas winters arent so short that you cant find the time to swap heads at a later date; say 2025?
And maybe in a year or two the bug bites, and youll be contemplating some performance heads, and kicking yourself for the money you spent on the hardened seats, today.
JMO
 
SGBARRACUDA said:
Do the math you spent over $2500.00 over 87 octane during that 50,000 miles. Cheaper and the correct way for the OP to have the harden seats added now.
Click to expand...

The Road Runner 383 had around 10:1 compression ratio, and iron heads. You had to run at least 93 octane in it. I think the Amoco Super-Premium was even higher than that. Perhaps you missed the point of my post: I ran unleaded gas in a high performance engine without hardened valve seats for over 50K miles with no apparent damage.
 
69_340_GTS said:
The Road Runner 383 had around 10:1 compression ratio, and iron heads. You had to run at least 93 octane in it. I think the Amoco Super-Premium was even higher than that. Perhaps you missed the point of my post: I ran unleaded gas in a high performance engine without hardened valve seats for over 50K miles with no apparent damage.
Click to expand...

No I understand your point. I was referring to the OP situation, If he installs the hardened seats now, he won't have to run Lead additive or special fuels.
 
stainless valves are a non-issue, its the seats that get worn. I say run it until you start getting some issues, then rebuild them, check that..REPLACE them with some post leaded gas heads. Installing hard seats in early heads is more expensive than just buying some hardened 302 pulls. Youll see the effects much sooner with mechanical rockers as you can gauge the valve sink over the preload.
 
Let me think about this a second. As the seats go away the valve lash tightens. Correct?
 
I put hardened seat in my 67 slant 6 because even using lead replacement additive I still had seat erosion. way back when, it was not that expensive, and it was exhaust valves only.

If you do it now you won't have to worry. I don't remember when lead free gas came into to usage. but I think if heads were made prior to lead free gas it would be prudent and one more thing to not worry about.

Omar
 
Busted.But observable non-the-less
I think they started phasing unleaded in around 72, up here. And I had heard that Chrysler was expecting it earlier, hence the rumor of hardened seats coming on line in 71. Heresay at best.
 
toolmanmike said:
Let me think about this a second. As the seats go away the valve lash tightens. Correct?
Click to expand...
yup, the stems rise in the head. and it starts a self destructive cycle of shortening the valve to seat time (valve clearance) and thats what cools the valve, hence burned valves too.
 
x2 on that Pishta. This becomes more pronounced as valve seat pressure increases.

69_340_GTS: IIRC the Amoco Super Unleaded ran 100-102 octane at the pump.
 
pishta said:
yup, the stems rise in the head. and it starts a self destructive cycle of shortening the valve to seat time (valve clearance) and thats what cools the valve, hence burned valves too.
Click to expand...

I better run my valves this spring. I didn't do it last year. Just a couple thousand miles though. tmm
 
If you had not done the heads already i would say add the hardened exh seats.
My 340 ran 12 years on non hardened seats with out a problem. It got a gal of leaded racing fuel every time i raced it. which was a couple times a mouth in the summer, unleaded all the rest of the time.

I replaced my 360 heads for a set of X heads and had them install hardened seats in it.

I have been told (don't know how true it is but.....) the first 1000 miles is the most crucial time for the lead treatment, that the lead don't go a way and is really not necessary after that except in extream condition such as a motor home or truck trailer combo.

street car, drag racing, don't put enough heat/time on the valve to cause the erosion.
 
No Model T ever had hardened seats. The last Model Ts were rolling off the assembly line right when tetraethyl lead was being introduced in gasoline, so all they had was unleaded fuel and they lasted a long time. I know a gentleman in fact with an original Model T in this county still running and the engine has never been into. He drives it a pretty good bit.

The main cause for valve seat recession is running with no or a dirty air filter. Dirt particles find their way into the engine and get between the valve and seat. Grinds seats to pieces.

Another less popular cause is when stellate faced valves are inadvertently put into heads with non hardened seats. Those valves are much harder than the seats and will ruin them in short order. The valves and seats must be of a similar material in order to last like they should.

Also, if the application is to be heavy duty such as a truck, hardened seats were installed. I have a 1956 331 Hemi on the stand and it came from the factory with hardened seat inserts installed because it was in a 56 Dodge D500 dump truck. Chrysler knew the rigors those motors were going to go through.

Extra resistance on an engine such as heavy vehicle weight or pulling loads makes exhaust temps go up. This is easily proven looking at an exhaust temp gauge on a diesel truck. Stand on the gas and watch the exhaust temp go up.

In applications like ours, light A bodies, hardened seats are just not necessary. Hot rods generally run cooler because their owners don't want them running hot. So they routinely have extra capacity radiators, high flow water pumps and thermostats and high performance fans to help keep temperatures down. This also has a drastic effect on exhaust temps.

Plus, you will always have the grim possibility of a seat working loose and letting go. With no seat insert, that is not a possibility.

Keep your air cleaner element changed regularly, keep your temps down and you will never have a problem with running non hardened seats.

It's just another stupid passed down myth just like the 3000 mile oil change.

Believe what you want. That's the truth.
 
I once had a valve job done to a 340 and didn't get hardened seats. In less than 10,000 miles the engine was running rough, and when I took the rocker arms off, some of the valve seats were so beat to ****... The #7 exhaust valve was sticking up 1/4" taller than the rest. And a few others were also, but not as bad as #7....

Now I always get hardened seats on the exhaust valves....
 
You must log in or register to reply here.
-

Back
Top