Hi M,
That is a wonderful engine you have created there, something you should really be very proud of.
After many years of playing about with and making steam engines, I have come to the opinion that easiest is usually the best.
To put it bluntly, if an engine is running at all different speeds, then lubrication needs to be controlled to match that requirement. Even ambient air temperature will affect how steam oil flows, so you should always err on the side of over lubrication rather than trying to get it perfect for all conditions.
Unfortunately you can be chasing your own a**e trying to get a perfect system, so the easiest way is to use a system that although not perfect, will give the engine protection from the lowest to highest oil demand.
That way can be easily achieved with a single non adjustable hole to allow oil in. For an engine of your size, I would use a fixed hole size of either 0.8mm or 0.9mm (that would be based on a boiler pressure of between 35 to 45 PSI). For one of lower pressure, say a Mamod type, a hole of 1mm to 1.2mm would be required. These sizes are not written down anywhere, but based on my personal findings.
You could go over the top and use an oil feed pump as they use on model locos, which admits oil based on the engine speed.
You have a choice, either you use the engine to play about with, or use it for what it is intended for. The first one can have a play with adjustable system, for the second, I would go with a fixed hole size.
You have to be very careful when putting steam engines into models. For say in a model boat, as you propose, you can spend more time fiddling at the lakeside than actually sailing.
What isn't there, can't go wrong.
Hope this helps (or maybe confuses even further)
Bogs
