engine cleaning

If the engine does not need disassembly because of a close encounter with the flying field/unplanned landing, I typically use brake cleaning spray that is sold in auto parts stores. It effectively blows the dirt from the engine, dilutes castor and leaves the surface clean.

If disassembly for a more thorough cleaning is needed, or to degrease the cylinder inside before e.g. devarnishing, I usually snatch the nail polish remover bottle from the toiletries of my wife, and put a few drops of acetone-based fluid on an earbud to access and clean the cylinder and other engine parts.

Then a few drops of Bernie's after run oil will suffice for corrosion protection and lubrication until the next start-up.

Anything is better than nothing.

WD40 is , as said previously (and everything that has been said is correct), primarily a water dispersant

A lot depends on how long and engine will remain unused.

With diesel engines that simply love castor oil - I run through a fuel mix with synthetic oil for a couple of minutes. This removes the remnants of castor oil without devarnishing. Longer runs will devarnish (if thought necessary) but care needs to be taken not to let the engine overheat. That is followed by a couple of drops of after run oil although I have used fine oils like sewing machine oil and gun oil.

I do the same with glow engines but I mix my own fuels and have quite a variety.

Typically fresh castor fuel (without starting the engine) is a good solvent for medium term storage (Do not do this with a diesel - it will fire up as you turn over the engine!)

However, there is an issue with glow fuels that affects 4 stroke engines noticeably. Glow fuel is quite good at absorbing water and during the combustion process can form nitric acid, nitric acid and aluminium don't get on with each other. WD40 will rid this and as an expedient is perfectly fine but not for long term storage.

Quite a few engines pass my way and I have to say that I have only seen a handful that have shown signs of acid attack. These engines have been otherwise pristine - they hadn't been run long enough for castor fuel to protect them or they had been run only with synthetic oil and then left.

Where castor oil has been involved - a couple of drops of after run oil works well. A few years storage and the engine will gum up.

Over cleaning, particularly on steel/cast iron cylinders/liners can be a bad idea removing all the varnish.

I do recommend though - regular oiling and turning the engines over but not with new ABC type piston/liners. Don't go over compression on these.

I have after run oil that I am happy with. I am asking about cleaning the outside of the engine after running it to lean off all the oil, but also to protect from oxidation. My engine crankcases are getting darker in color as time goes by and I wondered if the WD40 was causing it. Some of my engines are almost black.

Be careful with using isopropyl alcohol to clean any engine with ball bearings !!
The 91% isopropyl has 9% purified water as its inactive ingredient to make a 100% liquid.
The cheaper 70% alcohol has 30% water, etc....
WATER AND BALL BEARINGS DO NOT MIX WELL !!
I personally use carb cleaner to clean all engines with no plastic components since it is made for aluminum/zinc/pot metal.
It's stronger and more toxic than break cleaner but proper care and eye protection are mandatory for any chemicals.
As noted earlier, Marvel Mystery Air Tool is, IMO, the best after run and storage oil since it has rust inhibitors and WD40 water displacement additives. Some swear by ATF also since neither have solids in suspension that gum up over time...

YMMV....Steve...