do you have to install harden seats on 906 heads

[BigBlockSam]

i was always led to believe that you have to install harden seats on 906 heads or they will burn out thevalves . because of the unleaded gas. my friend is a machinist and builds heads every day of his life. he says in all the years that he's been doing it he's only run across a couple of burnt valves in 440 motors. now i don't know what to believe.  I've always done both intake  and exhaust. or is it OK to only do the exhaust. Rene

[Blown70]

CudaKen would tell you that you do not have to.  I am up in the air.  But if I was doing some heads I would pry do it.


Tom

[Just 6T9 CHGR]

My 915's dont have them......I do run a lead additive/octane booster though

[694spdRT]

Since Chris admitted it I will too. 

My 906's don't have hardened seat either. I run a lead additive and don't put a ton of miles on either.

[dodge freak]

I hear its high rpms and high heat thats does them in. Drag racing, thats what some call it.

[is_it_EVER_done?]

There are really two factors that would determine if it was necessary. The first is how many miles do you actually drive your car? The second is how bad are the existing seats (40 year old heads)?

Unfortunately the two are not separable, since if you put 10,000 miles or more on your car each year, hardend seats will be necessary in order to not have to do the valves every couple of years, and if the heads are allready worn out from decades of use, it would be silly to put non hardend seats in them. On the other hand, if you only put a couple hundred miles on your car each year, and you're not trying to get your dragstrip ET down to it's lowest possible level, a simple valve job is all that's necessary.

The biggest problem is not burning valves, it's seat recession. As the valves sink into the worn (non hardend) seats, and valves rock in worn valve guides, port flow suffers exponentially. However the absence of lead in gas can/does cause the valves and seats to burn, which requires a new valve job and valve (which further sinks the valve). In addition, depending on the quality of the machinist/equipment that installs hardend seats, you run the risk of a seat dropping out and destroying your engine -- as seat replacement becomes less and less common, the seat dropout becomes more common, as some machinists have never done a seat replacement, and therefore have no experience with it.

Your best bet is to either use a set of 452 heads as they already have hardend seats and flow better than 906's, or If you are going to have a set of heads completely rebuilt, you will be much better off going to new Edelbrocks (which have hardend seats and larger exhaust valves), as it's all to easy to sink half (or more) of the cost of new E-heads into rebuilding stock heads, and the E-heads are pretty much guaranteed to give you a 35-50 HP gain over the stockers with absolutely no other changes.

[deathcharger71]

i just rebuilt my first engine and i put hardened seats on the exhaust valves. when i took the heads apart the exhaust seats were pitted to hell and i imagine leeked a large amount, which would be the reason why i lost so much power over the last few years. but the intakes wernt pitted at all so i just gave them a 3 angle valve job. with the right machines its actually very easy as long as you take your time, i wonder how much money i saved by putting in new valve guides, hardened seats and 3 angle valve job myself...

[BigBlockSam]

i didn't know that the 452 heads flow better than the 906. i have several sets around here some were.
the last set of heads that my friend did for me come out outstanding. they are  906 heads , oversized stainless valves, new guilds, comp cam springs and molly retainers. i put harden seats on both intake and exhaust. ported and polished. there on the 440  sixpack motor that I've built for the daytona. my friend runs the shop and does it on his own time for me for half price. it takes a long time  but i don't care. i just gave him a set of 906's to build for me . milder ones. stock valves and only harden seats on the exhaust side. one hand washers the other, I'm building a bass guitar for his son.
  as for the Eddy heads, i don't like to put aluminum heads on big block mopar that i use mostly for street use. they like to run hot and traffic is a killer around here. the two differant metals cool at differant rates. i don't want any problems in the future. Rene

[dodge freak]

On those eddys heads I agree, no aluminum heads for me also. Thats another thing that stinks about these new cars. Intakes thats ok but heads no way. Feel sorry for these kids today, theres no way they are going to get these new motors the factory is making today to run great -if they run at all 30-40 years from now. Well I be dead so why should I care. Maybe you won't even have gas stations by then but then maybe so. I bet some of our cars will still be kicking some butt 40 years from now, if you still can get gas.

[RallyeMike]

2nd on the set recession problem. I had a piar of 906's that I ported and ran on a street car since they did away with leaded (20 years?). I never used additives. 30,000 miles later the valve seats on the exhaust side were recessed to point that this year when I removed them, the machine shop said they were unusable.

[TylerCharger69]

It's simple.....if the car originally ran on regular gas,  not unleaded..then the answer is yes....you need to incorporate hardened seats.  Unless of course you run some sort of additive to provide that "cushion"  Whetever the heads are  906s  or...whatever...if they ran regular gas originally...then yes....have hardened seats put in.   Nothing worse than a sunk in valve  rendering a perfectly good set of heads useless......just my 

[tan top]

There are really two factors that would determine if it was necessary. The first is how many miles do you actually drive your car? The second is how bad are the existing seats (40 year old heads)?

Unfortunately the two are not separable, since if you put 10,000 miles or more on your car each year, hardend seats will be necessary in order to not have to do the valves every couple of years, and if the heads are allready worn out from decades of use, it would be silly to put non hardend seats in them. On the other hand, if you only put a couple hundred miles on your car each year, and you're not trying to get your dragstrip ET down to it's lowest possible level, a simple valve job is all that's necessary.

The biggest problem is not burning valves, it's seat recession. As the valves sink into the worn (non hardend) seats, and valves rock in worn valve guides, port flow suffers exponentially. However the absence of lead in gas can/does cause the valves and seats to burn, which requires a new valve job and valve (which further sinks the valve). In addition, depending on the quality of the machinist/equipment that installs hardend seats, you run the risk of a seat dropping out and destroying your engine -- as seat replacement becomes less and less common, the seat dropout becomes more common, as some machinists have never done a seat replacement, and therefore have no experience with it.

Your best bet is to either use a set of 452 heads as they already have hardend seats and flow better than 906's, or If you are going to have a set of heads completely rebuilt, you will be much better off going to new Edelbrocks (which have hardend seats and larger exhaust valves), as it's all to easy to sink half (or more) of the cost of new E-heads into rebuilding stock heads, and the E-heads are pretty much guaranteed to give you a 35-50 HP gain over the stockers with absolutely no other changes.

           





there is a bit of a gray area on this subject . true   906 heads need hardend seats put in them to run unleaded gas , as the seats will be worn away under extended wide open throttle runs in a few thousand miles or less depends how much you stand on the motor , alternatively just  granny shifting  wile going to the grocery store they might last 20 30 40 thousand before the need a valve job or need to be junked .  452 heads already have hardend seat , that is the quickest easiest swap . buy memory they flow almost or as good as 906 head in stock form any way.

[deputycrawford]

I used lead additive and my valves sunk so bad I tore the egine down and had it all done at once. Do it once.

[Chryco Psycho]

I always install hard seats but exhaust seats only

[skibuff]

I've been running my 440 on unleaded fuel since 1990 and I have not yet had any problems with burnt valves.  It's a street car and I run it hard whenever the urge occurs.  The car runs very strong.  I have been told, and my results verify it, that you only need to run hardened valve seats if you are regularly running the car hard at high rpm. 

However, I am plannning on tearing down the engine in the near future and hardened valve seats are on the agenda.

Skibuff

[dodge freak]

When you do let us now how the heads look like, if you find any sunk valves or if they all are fine.

[Crazy440]

This all brings a question to mind.  What year did Ma Mopar start using hardened seat in 440s?

Crazy

[Chryco Psycho]

452 castings are the Only 440 head with hard seats & they are only induction hardened so it is a very shallow hardening with a valve job the hardening can be cut through
it is very unusual for the intake seat to erode as the intake valve is cooled by incoming air while open , the exhuast seat on the other hand is red hot when open & tends to weld itself to the seat when it closes & cools , the exhaust seat can erode quickly with heat as stated above 

[andyf]

The 906 heads on my 1970 383 powered pickup truck had the valves sunk in a ton when I tore it down.  I was able to save the heads by putting in larger valves and hard seats.  The engine seem to run okay but the several of the valves were sunk down quite a bit when we tore it down.  So people who say that their engine runs fine without hard seats might not know how things actually look inside the engine.  I know I didn't.

[TylerCharger69]

Not only  does  the temperature have affects on the seats...but  also   when cars ran on regular leaded fuels......the lead provided a cushion between the valve  and the seats....a form of lubrication...which was taken away  when unleaded gas came into play.    That's why many...including myself  use an additive  (Marvel Mystery Oil)  even though I have hardened seats installed....Once I month I mix  some VP fuel with some unleaded with the additive together.  But...shhhhhhhh.     lol