Graeme
The info you need to know is this:-
Sentinel Crankcase Oil is designed for use where there is a likelyhood that the oil in the crankcase comes into contact with steam and consequently water.
The crankcase oil is developed so that if left standing the oil and water easily seperate and the water can be drained off, leaving the oil fit for use again, and minimise the corrosion of the internal parts
The S type Sentinel engine is single acting and it is therefore basically the mechanical fit of the pistons, rings and bores that prevent steam going into the crankcase, in reality an S type needs this type of oil.
The earlier double acting Sentinel engines - i.e the Standard, Super and DG are double acting, and have glands on the piston rod that should prevent oil contamination. In reality it doesn't, but the problem is far less than with an S type.
Then in the UK we have the condensation problem, our toys are not in continuous use, and given the moist aura surrounding a steam engine, and large masses of metal condensation within the crankcase can cause a significant amount of water in the crankcase. We are obviously talking full size here.
I think in practice it is common over here for Sentinel Owners to use 'Crankcase Oil' in all types.
Now, in your model application, some details of the engine construction may be usefull, I have noticed that wagon 'models' tend to bear only a passing resemblance to the full size prototype and therefore it is difficult to comment.
However some of my thoughts.
- Your engine is likely to be small, and the oil contained in the crankcase small, it may be simpler to use normal bearing oil and simply change it regularly. I guess it will only hold a pint or so in anycase?.
- As nature does not scale, I am not sure how much water will enter your crankcase (nor am I sure of the mechanical arrangements in any case), is it really plausible that in a pint or so of crankcase oil that you can expect to successfully drain an eggcup full (or so) of water?,
- Is the crankcase arranged so the internal surfaces will fire the water to a low point where there is a suitable drain?