Another thing I was anxious about was whether the heat exchanger, which is leaking, could be repaired. The leakage only occurs when the heat exchanger gets hot, and because of the construction it is unfortunately impossible to find the leakage, and a repair just as impossible. So I need a new one - what a bummer!
The cylinder head is now removed and everything looks very nice. There is no edge in the cylinders, however, there are clear traces of honing. So the pistons have been out of the engine not so long ago, as the very low oil consumption (nothing) and the fine oil pressure also indicate, so the engine has probably been rebuilt at some point.
Now that the cylinder head has been removed, I have the opportunity to take a closer look at the plate that was placed under the cylinder head, and I came to wonder if the engine was actually designed like this from the factory. And yes, it's a BB43F (F for fotogen, which is the Swedish name for kerosene). The engine type was made for both petrol and kerosene, with the BB43B gasoline engine having a compression ratio of 7.5: 1 and 40 hp, the BB43F kerosene engine having a compression ratio of 5: 1 and 25 hp. To convert the engine to the gasoline version, the copper plate will not be mounted again and the cylinder head studs and pushrods will have to be replaced with shorter versions from a gasoline engine.
Some may think it is a bit brutal to expose an old engine to such an increase in power, but I'm pretty sure it won't do any damage considering the good condition of the bearings, and the extra power will be nice to have, just as the gasoline economy probably will be improved. 40 hp is not much for a 1.4 liter petrol engine, and it will never do any hard work.
The removal of rust and old paint is fast moving forward. I now have only the cylinder head and seawater pump left to clean. I also renovated the carburetor and made it look nice - it is a cast iron carburetor, so it had to be painted as well. New seals and float valve are installed, and everything has been looked after and cleaned.