Unleaded fuel valve wear theory

[Truckedup]

Vintage bike guys have been saying this lately,

Microwelding of the exhaust valve and valve seat is now thought to have occurred due to the increase of flame front speed when the switch to unleaded came about. The increased combustion pressures caused 'micro welding' in older style motors that had the valve seats machined into the cast iron head. Retarding the timing of the engines reduced the combustion pressures and proved to be an effective short term measure in the switch to unleaded fuel. The long term solution was hardened steel valve seats

Some also say that E10 fuel is more abrasive than non ethanol fuel and it causes valve stem wear...
What do you think about these statements?

[user-30257]

How did the alcohol guys do it in the 60s-70s then.

[Dave Koehler]

Not so much the ethanol as the lead that got removed decades ago.
Heard all the horror stories back then and expected to be overrun and get rich fixing all the heads.
Funny thing happened. Not that many heads had the seat wear problem due to the lead removal. Never did figure that one out.

[tresi]

The few things I seen made it sound like it depended on how hard the engine was ran. Getting groceries or going to grandma's not too bad. Pulling your racecar or camper different story.

[allencr267]

a lotta people liked this stuff for a long time & I don't recall any complaints about valve damage/recession.

[PRH]

The few things I seen made it sound like it depended on how hard the engine was ran. Getting groceries or going to grandma's not too bad. Pulling your racecar or camper different story.

That......... and also hot rodded street motors with aftermarket cams that have faster closing ramps than oe, running higher spring loads, loose converters and lower rear gears(making for higher cruise rpms).

Until the cheap aftermarket heads really took off, when a fairly large chunk of the work coming in the door were oe heads......... I used to install tons of exhaust seats.
Many times the valves receded enough to where the hyd lifters were bottomed out.

Aaahh..... the good ole days.

[MadBill]

Vintage bike guys have been saying this lately,

Microwelding of the exhaust valve and valve seat is now thought to have occurred due to the increase of flame front speed when the switch to unleaded came about. The increased combustion pressures caused 'micro welding' in older style motors that had the valve seats machined into the cast iron head. Retarding the timing of the engines reduced the combustion pressures and proved to be an effective short term measure in the switch to unleaded fuel. The long term solution was hardened steel valve seats

Some also say that E10 fuel is more abrasive than non ethanol fuel and it causes valve stem wear...
What do you think about these statements?

Total bunk.
o (Turbulent) flame front speed in a given running engine is essential the same for any conventional fuel; otherwise big changes in spark advance would be needed.
0 For any substantial fuel-induced combustion pressure increase, a matching power gain should result. Short of significant nitro content it doesn't happen.

It's the lack of the lubricating effect of the lead that causes problems, but very much load-related. The unhardened seats in an early SBC running unleaded fuel may last 150,000 miles in an inner city taxi but less that 5,000 in a cube van continuously running near-WOT in highway service.

[pamotorman]

a lotta people liked this stuff for a long time & I don't recall any complaints about valve damage/recession.

I remember my dad calling that white gas. he burned it in his blow torch and gasoline lantern.

[engineguyBill]

The lead in leaded gasoline acts like a lubricant, therefore engines running leaded gasoline could use valve seats ground directly into the cast iron head with no problems. Unleaded fuels necessitated the use of induction hardened seats or proper seats installed into the heads as a production process. Due to the heat of combustion, exhaust seats were more of a problem than the intake seats. Installed thousands of replacement seats in all makes of OE heads in the 70's and 80's.

[engineguyBill]

"White gas" ius a very low octane gasoline that was often marketed by cut-rate gas stations back in the day. Very cheap and just abount any engine would ping when it was used. White gas was also marketed by Coleman as a fuel for their gas lanterns, camp stoves, etc.

[modok]

If the seats wear out, install seats.
how to tell? Check valve lash

Another reason to install seatrings is to prevent the exhaust seat cracking and extending too far to fix with a seat-ring, happens ALL THE TIME

[Truckedup]

The lead in leaded gasoline acts like a lubricant, therefore engines running leaded gasoline could use valve seats ground directly into the cast iron head with no problems. Unleaded fuels necessitated the use of induction hardened seats or proper seats installed into the heads as a production process. Due to the heat of combustion, exhaust seats were more of a problem than the intake seats. Installed thousands of replacement seats in all makes of OE heads in the 70's and 80's.

Is the heat of combustion hotter with unleaded gas as compared to leaded gas in the same same engine?

[engineguyBill]

Is the heat of combustion hotter with unleaded gas as compared to leaded gas in the same same engine?
[/quote]

I don't think there is a significant difference between the combustion temperatures created by unleaded fuel, as compared to leaded fuel. The seat/valve damage/wear issue is pretty much attributed to the lack of lubrication which the lead provided. Most emissions-era engines do however run at higher engine temperatures (192-195 degree thermostat) as opposed to vintage engines, which typically ran 180 degree thermostat.

This said, engine temperature does not have a significant affect on combustion temperature, however combustion temperature can have an affect on engine temperature. Remember, most of the combustion temperature is absorbed by the piston crown and transferred to the cylinder wall/cooling system via the compression rings and the valve/valve seat interaction to the cylinder head cooling system.

[Schurkey]

Consider a valve seat, having run for thousands of miles on "lubricated" leaded gasoline, then switches over to unleaded gasoline. Service life on unleaded may be satisfactory--assuming fairly light load.

The seat was work-hardened as the engine ran, and the lead "lube" slowed seat recession. Then when the lead is eliminated from the fuel, the seat has hardened enough to survive better than a "fresh" seat that cuts into the softer parent metal and then run on unleaded fuel.

I have the sense that lead in gasoline is comparable to "zinc" in motor oil. Both deposit a layer of protecting film on the associated parts, and normal engine operation tends to scrub-off that protective layer--but better to scrub off the protective film than to scrub off or erode the base metal below.

[piston guy]

My experience mirrors Schurkey's. "Old" iron heads that ran on leaded gas have "work hardened" seats. In '72 or so when the unleaded was being introduced , "new production" heads did not have hardened seats and seat recession was rampant on "new cars" until manufacturers went to induction hardened seats. The problem had "the masses" thinking ALL heads had to be converted to hardened ( replacement ) seats to survive. Not every person did so and I see heads all the time that have NO seat recession and NO hardened seats. If they haven't sunk by now I see no reason to cut them for hard seats. Maybe I'm wrong.