Exhaust seats and leaded/unleaded fuel

[Bolted to Floor]

OK guys, I need more of an education. Dealing with the exhaust seats before and after the switch from leaded to unleaded fuel. Somewhere along the way, the fuel changed. New cars after this point got different exhaust seats. No way all of the older cars got upgraded.

My 69 F250 with a 360-2V never had the exhaust seats changed. I bought it from my grandparents with 145K in 89. Rebuilt the motor at 150 and drove it more than 60K miles through the late 90’s. I never noticed any difference. May have not been smart enough to notice either!!

With unleaded fuel, why are the different exhaust seats required, or is it more like a recommendation?   

I ask because I want to make use of some C6AE R heads that I have. I already have the FPA's with the CJ flange and should seal with these heads. I don't want to spend a lot of money on them, porting and CJ size valves are out also. My other head options are D2's and the 390 GT's. Somewhere in the distant future, I will upgrade to aluminum heads, just not sure when.
Thanks in advance for the answers.

[fe66comet]

You have to go pretty far back to find a head without hardened valve seats. By the late 1950s most everything had replaceable hardened seats due to increased compression and unleaded fuels.

[HiPower]

Unleaded fuel dates to the mid - late '70's, not the fifties.  Any domestic gasoline before this change had pretty high levels of tetraethyl lead in it, which also drove the high octane ratings of gasoline from that era.  Any domestic vehicles made before this had unhardened exhaust valve seats.  As the lead in fuel promoted cooling of these seats, it's not uncommon for these older engines to burn exhaust valve seats when using unleaded.  The cure was switching to a hardened seat, typically done with a Stellite coating on the seat/valve, which better resists the high temps.

[RJP]

Unleaded fuel dates to the mid - late '70's, not the fifties.  Any domestic gasoline before this change had pretty high levels of tetraethyl lead in it, which also drove the high octane ratings of gasoline from that era.  Any domestic vehicles made before this had unhardened exhaust valve seats.  As the lead in fuel promoted cooling of these seats, it's not uncommon for these older engines to burn exhaust valve seats when using unleaded.  The cure was switching to a hardened seat, typically done with a Stellite coating on the seat/valve, which better resists the high temps.

One correction about lead, it does not cool the valve, it lubricates the valve and seat preventing the transfer, on a microscopic level, of metal from seat to valve face. It is also not uncommon for a much cooler running intake seat to "sink" as does the exhaust seat from lack of lead as a lubricant.  Burnt valves are not a direct result of unleaded fuel but may burn as they are no longer in firm contact with the seat and can't cool properly.

[427Fastback]

I pulled a 69 390 truck engine apart last year that had spent its life up here in Canada.The exhaust seats were gone....as in destroyed..
I pulled the iron heads apart that were on my 427.They had about 17,000 miles on them.They also were destroyed...No damage to the valves but the seats are history...
I then yanked the heads (67 289) back off my 289 roller engine in my 67 but they were fine.Its a very low mileage engine but I cant put seats in it as its got 1.9 and 1.6 valves and there is just no room left..

I have aluminum heads for the 427 and I will just have to use additive in the 289 for now...

My opinion and general understanding of the damage unleaded fuel can do has been severely updated....

Cory

[fe66comet]

The only engines I have ever had an issue with is late 50s down. Running an engine lean and advanced for power will smoke seats, but even my old tractors from the 30s, 40s and 50s have no issues. Valve rotators help a lot with wear also.

[427Fastback]

None of the engines are run lean or are over advanced...My flat head Dodge tolerated the un leaded much better than the FE's did...

As far as I know the only FE head with any thing close to a good exhaust seat are the D2 heads...

[fe66comet]

Man I have run FE engines for 200,000 miles in service trucks with no big issues, wonder why? They smoked some but did not rattle or buck under load, which was constant with a ton of pipe and threding equipment in the tool boxes.

[bn69stang]

It s my understanding that hardened seats started in production about 1972 , and up and the leaded fuel lubricated valves and seats . And by the way leaded regular gas stayed at the pump til 1988 .. Bud

[Bullitt]

It s my understanding that hardened seats started in production about 1972 , and up and the leaded fuel lubricated valves and seats . And by the way leaded regular gas stayed at the pump til 1988 .. Bud

We had a form of leaded gasoline in Colorado until 1994.

Josh

[Richard F]

I believe lugging an engine affects it more than the lack of lead; I have seen many heads that are fine without hardened seats, mine and others.  Truck engines seemed to be hit the hardest as they would be loaded worse than car engines.  If I were to run old heads, if they had good seats I wouldn't change them...just my opinion and experience.

[drdano]

When I got my '62 Galaxie back in 2005 or so, it had what I was told was an original motor in it.  Later down the line I pieced together it was a '64 era dealer replacement shortblock with OEM '62 top end on it...anyway, never had hardened seats in what I'm pretty sure were OEM '62 factory heads.  There was a jug of lead additive in the spare tire well and the prior owner told me to use it religiously, to which I immediatley forgot.  I had a valve job done shortly thereafter and the machine shop asked if I wanted hardened seats installed.  I forgot about the jug of lead additive and figured, "hell, if they aint sunk already, I'm good!" and didn't have the hardened seats installed.  About 10k miles later, the motor started feeling pretty tired.  It had 90k on the odometer.  When I tore it down, it was pretty worn and ready for a refreshening.  Oh, and half the valves were sunk into the heads...some worse than others.  I'd have the hardened seats installed in whatever heads you choose to run.

[Bolted to Floor]

Thanks for the information and the education. I went Googling to forums far away and found pretty much the same results as here. Some have had issues and others have not. Several mentioned the use of a lead additive, but it could separate in the gas take if it sets a while. I will look into the cost of adding the hardened exhaust seats to the price of a valve job and just see where the pricing goes.

All of this hinges on if the guides can get away with knurling or need to be replaced. If the heads need too much work, then the whole idea may get scraped anyway. 

[RJP]

A couple of comments on exhaust seats, seat recession and the need for hard seats. First: some heads under certain conditions will "work harden" on their own and is usually related to use. Around town at low rpm, low load and low heat in the exhaust will not usually need hard seats. The seats will surface harden similar to "case harden" pieces done by a heat treating company. High speed highway driving for long periods of time and/or heavy loads where exhaust temps are high valves will almost always sink into the heads. I have done heads where both intake and exhaust were sunk and both sets of seats needed replacement and I have done other sets of heads [EDCs-C1s-C4s-C6s-C8s] where the exhaust seats acted like they were induction harden similar to what the factory does for use with unleaded gas but not as deep.  D2 heads, from early 72 and later used factory induction hardened seats.  FWIW, Every set of heads I do gets hard seats, not worth the worry of sinking valves, loss of compression and having to do the job again. 

[427Fastback]

Interesting....the 390 heads that I had with the sunk valves were the factory heads on a 69 F-250 4x4..Truck was from Alberta and I don't know its story..

My 427 Heads were C8's with CJ valves.90% of the miles on them were Mountain hwy's,climbing mountains and any other long winding hill I could find.Engine lives at 3000-4500 rpm.Even if I was city driving I didn't lope around....
I will put seats in the heads and use them on another project..We have had unleaded here since the mid 80's.....Cory