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Old 05-17-2013, 07:25 PM
st3gamefarm st3gamefarm is offline
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Originally Posted by Dave57210 View Post
One of the "everyone knows that" areas of "common knowledge' (which means "usually wrong") is that the lead was the lubricant for the exhaust valve. (oil would be burned off due to the temps of the valve) so only lead would do the job to provide a "babbit bearing" sorta lube for the valve stem and for the actual valve as it rises out of and sets back into the seat.

Tetraethyl lead was a main component in raising the octane of gas from the abysmal levels of pre-WWII to the stuff that hi-po engines could actually use.

When lead was abolished from gas in the 70's, many engines experienced valve recession and some also had greatly increased wear on valve stem guides and so the "common knowledge" came about.

I assume this is a Lycoming IO-360? (The one I owned for a while in a PA-28 was the 150 hp version and only needed 80/87 fuel) As I recall, the 100LL usually lead-fouled the plugs something fierce, but was a compromise fuel supposedly better than the (then common) 100/140
O-360, not IO-360. (not fuel injected) The 150 hp in your Cherokee would have been an O-320. Actually, had this engine been an I0, the valve probably would not have been sticking as much. Due to better fuel metering.
The point that I was trying to make is to not fall into the OWT of lead in your fuel being beneficial to your engine. It is not, and never will be.
They quit makin' 80 octane avgas back in the very early '70s. An I haven't seen th' green stuff in as many years. so 100LL is all ya get, Some places offer mogas, but it's not legal to run it without the STc, and not all engines can get it, and in some cases, while you can get the STC, compliance is cost prohibitive. In some cases the STC is a simple matter of buying the paperwork, and a logbook entry. In other cases, it's all that plus extra fuel pumps, and different hoses, etc. And in other cases, it's not even available.
Nowadays, it's a moot point due to the alcohol in car gas. Which is a huge no-no in aircraft.
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