Caring for engines

Castor oil is a fantastic lubricant but after running it dries out and eventually gets to the point where the balls in the bearings don't roll but skid, the bearings will fail and when a bearing fails in use it can often result in grave damage to the rest of the engine.
Cleaning is often not successful as it is very difficult to wash out once the oil has dried.
After every days flying they should get a spray with WD40 or similar and then be lubricated with after run oil, there are many good oils suitable for this purpose, automotive automatic transmission fluid has been found suitable.
Some down the venturi, in the exhaust and around the prop driver. Put in a few drops and flip it over, a few more and flip it over, don't over do it and if you do and it locks as you try to turn it over simply allow the excess to drain out the exhaust.
Under normal circumstances it would most likely be fine for a week or 2 without doing this, but often a week turns into 2 then 3 and so on, and before you know it there is a problem which could so easily have been avoided.
For long storage ( more than a few weeks ) I recommend that the engine is removed from the model, spray inside and out with WD40 or similar, then lubricate with after run oil.
Wrap the engine in a rag and as long as you are sure there is no moisture present you can also pop it in a plastic bag and store it in a dry place.
If the engine is expected to be stored for only a few weeks then by all means leave it in the model but give it the oil.
Before starting for the first time flush it through with some fuel to wash the oil out.
With this treatment I have engines which have been used for years without a bearing change, and on the other hand seen too many with only a couple of hours running ruined through neglect.