[Public-List] Old gas engines

[Daniel Michaels]

It is not the high octane that you are looking for in 100LL it is the fact that it lasts for years without going bad. mix it in with regular fuel and you can let it sit for months without worry. Run your A-4 with some old rancid fuel that is all gummed up and see if it runs as well as on fresh fuel. Give and take, if you run your engine less than once a week or worse less than once a month the trade off is well worth it. I have been running 100LL mixed in my Taylorcraft 65 hp low compression engine and it starts every time on the first pull even after sitting for a month or over the winter for many months. My small engines at home however if not started and run frequently rarely start and run fine without some kind of tuneup.

Dan

--- On Tue, 8/31/10, Stephen Gwyn <gwyn at beluga.phys.uvic.ca> wrote:

From: Stephen Gwyn <gwyn at beluga.phys.uvic.ca>
Subject: [Public-List] Old gas engines
To: public-list at lists.alberg30.org
Date: Tuesday, August 31, 2010, 2:05 PM


Hi,

Just a quick note to remind people that for gasoline
"high octane" = "less flamable" not "high power".

The point of high octane fuels (running from higher octane automotive fuels or aviation fuels like 100LL to jet fuel and highest octane of all, diesel) is not that they burn hotter, it is that they don't ignite prematurely in high compression engines.

In such engines, the increase in temperature of the fuel-air mix as it is being squeezed on the compression stroke can ignite low octane fuels before the spark plug fires, causing knocking. Tetra-ethyl lead was used as an anti-knock compound, decreasing the spontaneous ignition temperature of fuel. It is amazingly poisonous, (you know, lead poisoning, except now it's in the air you breathe) so it has been taken off the market except for limited amounts in aviation fuel (LL in 100LL stands for Low Lead).

The Atomic 4 is not a high compression engine, and older (is there any other kind) engines in particular usually have fairly low compression. If you want your A-4 to run well, use low octane fuel. If you use high octane fuel, it will burn poorly since it won't be at its correct temperature when the spark goes off, causing decreased performance and increased fouling to due incomplete burning.

If you want high octane fuel, you can always use diesel,
which has a very high octane rating.

Stephen
#495 Quasar
(with a smooth running Atomic 4)





Still scraping by with the A4, while rebuilding the carb on the dock I met a lot of other people having engine troubles recently. I had a friend who is also a mechanic helping me.  He suggested the reason so many people are and will have trouble with older gas engines is the gas itself. These engines were built to run on leaded gas, the lead in the gas acts like a lubricant. The low grade gas at most fuel docks also has ethanol in it which would do just the opposite. You can purchase a lead additive from most automotive supply stores and if you can't bring in your own high octane fuel there is another additive to deal with the ethanol. Can't remember the name - it's blue.  These changes made an improvement in my engines performance. Thought I would share incase others are/were in the dark about this.



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