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My Radial Engine Experience.

Radial engines are mostly 9 cylinder (radials must be an odd number or multiples of odd numbers e.g. twin row). The cylinders are steel and the heads are aluminium and screwed to the cylinders. Very occasionally, following overhaul, some leakage between cylinder and head would occur.
A Pratt and Whitney 1340 cubic inch radial powered the first Airtractor I bought. In a short period some 5 cylinders leaked at the joint. The Australian dealer insisted they be replaced. Because they didn’t wish their products’ integrity to be questioned they said it was of my doing for I was a hard man on aeroplanes.
An aerial application operator who owned some 52 DeHaviland Beavers had their engine overhaul workshop based in Melbourne, only 200 miles from me. I later consulted them and they said this leakage sometimes occurs. They advised me to simply clean the cylinder at the joint and change it only if it continues after having flown 100 hours. I have had 15 or 16 engine changes during my time of radial ownership and never had reason to change another cylinder for that reason.

My first aeroplanes had 6 cylinder, horizontally opposed engines. The fuel consumption was between 50 and 65 litres per hour depending on the horsepower they delivered. Now my new aeroplane was powered by a R1340 and had a fuel consumption of 140 litres per hour. This volume made me somewhat nervous. So to reduce my cost I operated on low power. The oil consumption did not settle below 10 litres and hour and that too made me nervous. The alternative was gas turbines (jet) and cost some $300,000 each which I couldn’t afford. That is about half of what they cost today.

This engine and subsequently other R1340's I subsequently installed were overhauled in Los Angles by Aero Engines Inc. At this time an engineer from that company, a gentleman by the name of Vern Truman was in Australia and came to see me. He set me straight on the use on power setting; use more. I subsequently observed that production was proportional to fuel burn. Burn more, produce more. Simple. To clean the cylinders induce a Mercury outboard product called ‘quicksilver cleaner” through the engine manifold pressure gauge with the engine running about 700rpm. That was when the manifold pressure was low and the vacuum would suck it through. The super charger would distribute it to the cylinders. Do this then follow it with inducing Marvel Mistry Oil about once each 100 hours when finished for the day and the cylinder trash would be blown out the exhaust in the morning.
I operated the R1340 in an Airtractor for 5 years then traded it for an Agcat powered by R985 which I mostly had overhauled in Melbourne. I operated 3 Agcats; they were productive and easy to fly.
I bought a gas turbine Airtractor in 1994 and the fuel consumption averaged 170 litres an hour. 240 on takeoff. The production did head skyward and the cost of Jet fuel was only 35 cents per litre. I used to purchase it by the tanker load. Aeroplane operators today would be envious because my fuel cost was only 15 percent of my gross income. One should not fly these radial engines at night because one sees a blue flame flowing about 3 foot out the exhaust. One knows this is fuel burned after being exhausted and this too did initially created some anxiety. You may by now think I am a nervous person.

I have never known the composition of Marvel Mystery Oil so I looked it up, and here it is. I have seen it written about in this forum.

Marvel Mystery Oil is an automotive product of the American Marvel Oil Company,[1] founded by Burt Pierce in 1923.[2] It is used as a fuel additive, oil additive, corrosion inhibitor, penetrating oil, and transmission leak stopper and seal relubricator.
It is composed primarily of petroleum distillates, including mineral oil (60–100%), mineral spirits (10–30%), tricresyl phosphate (an antiwear and extreme pressure additive in lubricants, 0.1–1.0%), ortho-dichlorobenzene (a softening and removing agent for carbon-based contamination on metal surfaces, 0.1–1.0%), and para-dichlorobenzene (a precursor used in the production of chemically and thermally resistant polymers, <0.1%).