Unleaded Fuel Recessing Valves is a Myth???

[HotRodPC]

Had anyone ever head that unleaded fuel in non hardened seats tearing up older leaded heads is a myth???

I know it's not a myth and have known for a fact since about 89 it wasn't a myth. I found that pic of my head I took off of one of my trucks.

Just saying, believe it, it's true. Unleaded fuel DOES require hardened exhaust valve seats.

 

[HotRodPC]

Left alone, these exhaust valves could have recessed enough and possibly dropped the valve keepers off the tops of the springs then allowed the valves to drop in the cylinders trashing the motor for good, and scoring the cylinder walls bad enough it probably wouldn't even be a rebuildable block afterwards. Keep in mind, you ALWAYS need hardened exhaust seats in older heads.

 

[lusktommy]

Had anyone ever head that unleaded fuel in non hardened seats tearing up older leaded heads is a myth???

I know it's not a myth and have known for a fact since about 89 it wasn't a myth. I found that pic of my head I took off of one of my trucks.

Just saying, believe it, it's true. Unleaded fuel DOES require hardened exhaust valve seats.

Oh yes its a fact i agree, ive always heard that growing up and ive never heard anyone call it a myth until now i thought everyone knew that...lol

 

[HotRodPC]

Some of the Olds and Pontiac gurus call it a myth. It could be that Olds and Pontiac had hardened seats before the time is all, but I do know SBC heads need hardened seats. I think these were 71 heads and they recessed. I'm not even sure I can use them now if I had hardened seats put in them. Doesn't matter much though, there are much better options today, like Vortec heads. But, a Vortec heads need machined in the spring area if you're going to run over a .480 lift cam or even less if using 1:6 or 1:7 to 1 ratio rockers.

 

[bucket]

I've never heard it was a myth, although an older fella did recently tell me that the lead additive is not needed on an original untouched motor. He said there is enough lead buildup over the years to protect the valve seats.

 

[austinado16]

I see it on the British engines I've worked on. The cast iron seats get all pocketed and rounded, and that rounded shape starts making the seat surface on the valve head do the same. Does make for a big fat seating surface though!

 

[Christian Nelson]

Engine machinist told me the real deal on this, since I've seen plenty of old engines running for many years running unleaded with no problems.

He agreed, they are fine until someone cuts the valve surface and then uses unleaded.

The leaded gas cushions the valve seats until they get work/case hardened by running the engine. After this has happened, they are fine, absolutely fine. IN fact, this same guy said if you use lead additive until the engine is fully broken in, it should be fine to not use it after that.

The key is the fact that if you run it with lead for a while (I think he said the modern lead replacement did not work the same as using actual leaded gasoline- which can still be gotten) it will harden, and not sink.

Makes sense to me, since I have seen plenty of older engines run for a LONG time with no ill effects on unleaded, but they weren't rebuilt, no one did a valve job on them, so they were fine. Look at all the old tractors for example, farmall, case, etc, running unleaded for over 30 years now. My father in law has several 40's and 50's vintage tractors which he still uses working on his farm. Never a rebuild, no problems on unleaded gas. His dad used these tractors, he bought them from his dad, and he continued to use them.

Now, if someone lapped a new set of valves in there, they'd better put a hardened seat, or run real unleaded gas on the break in period.

 

[HotRodPC]

I just think it's cheap insurance to have hardened seats put in on your exhaust valves when you have a valve job done and then you odn't have to worry about it. Or use late model Vortec heads and be done. You might spend a bit more for Vortecs, but by the time you spend $25 X 8, there you've spent $200 more for old school heads and could've had Vortecs anyway. Sometimes, money is better spent elsewhere and punt the dinosaurs.

 

[SAATR]

For what you can get a set of used aftermarket or Vortec heads for, it's hardly worth fooling with a lot of the old school castings. The technology and performance difference alone is worth a few hundred dollars, at least to me.

 

[HotRodPC]

For what you can get a set of used aftermarket or Vortec heads for, it's hardly worth fooling with a lot of the old school castings. The technology and performance difference alone is worth a few hundred dollars, at least to me.

Exactly the point I was making above.