"Live Steam" magazine published by village press is a good source if information, but it is about 80% park scale steam trains, 10% boats, 10% stationary scale engines, and maybe 1% "working" engines. Most of the articles are in many parts, sometimes over years. HOWEVER, they also publish complete articles in book form, and that is probably the best way to get the info. The series on the Barrett steam car (VW conversion) was probably the best they have published with regard to making a steam engine do useful work in the modern world. Some of the larger model kits might make a HP or two and run a small genny, but small steam engines are not efficient due to heat loss.
Converting a gas engine to a steam engine that will keep itself turning isn't so hard, but making a _good_ steam engine (durable with reasonable efficiency and power) out if one is so hard you'd be better off starting from scratch. Just for starters:
-Gasoline engines need to shed heat, so have fins and such. In a steam engine, heat loss is power loss, so the cylinders are insulated (lagging) to keep the heat in.
-Gasoline engines have a problem with the head getting too hot, so it is a good idea to have a good heat path from the head toward the crankcase. Steam engines have a problem with heat leaking from the intake to the exhaust, so it is a good idea to put the intake in the head, and exhaust ports at the bottom of the cylinder (uniflow) and make the cylinder out of low thermal conductivity material like stainless steel.
-The poppet intake valves on a gas engine are arraigned to keep high pressure in the cylinder. The intake valve on a steam engin needs to be reversed so that it keeps the high pressure steam OUT of the cylinder. Reversing the intake valve basically requires a from-scratch new head. The high pressure supply steam will be very hard on the intake valve and seat. These parts are best made from inconel or similar alloy.
-The exhaust valve is the right way round, or you can cut 2-stroke style exhaust ports, like your OP suggested, making what is known as a uniflow steam engine. You have to make sure the rings don't catch in the port, so they need to be pinned so they stay in the correct orientation (see any ringed two stroke engine for example) It is best if you can exhaust a uniflow engine into a condenser (vacuum) so you are not fighting compression on the upstroke. Condensing engines are more efficient but bring along a whole host of other issues. So many that there were no successful reciprocating, condensing locomotives in spite of the fact that it would have solved the water supply issue which was a major problem for railroads. (there were some successful condensing steam turbine locomotives)
-Either you have to change the cam gears to 1:1 or make a second lobe on each cam, or your engine only makes half power. Some elect to allow the piston to operate the intake valve...works on a model engine, but is not a durable arraignment, and the resulting advance means the idle speed has to be kept pretty high so the piston can go over-center whilst fighting the inlet pressure. That also puts the valve spring right where the inlet steam corrodes it and takes the temper out of it. Best leave that scheme for model engines running on compressed air.
-High pressure steam will erode aluminum. Aluminum pistons need a stainless cap.
-An enclosed crankcase on a steam engine will end up with lots of water in it from blow-by. An open crankcase requires frequent oiling.
-etc. etc.
THEN, as if the engine were not hard enough, making a safe, efficient, high pressure boiler is nearly as difficult (if not more so) as the engine itself. Failure of the boiler can have horrific consequences, so most jurisdictions have stringent codes regulating the design, testing, inspection, and operation of steam boilers, and it would be prudent to observe such precautions even if not a legal requirement. You will either need to operate a condenser, or have other arraignments for water that will not foul or corrode your boiler. You may find a used engine to restore, but safely restoring a steam boiler is a major undertaking. Usually the original is scrapped and used as a pattern for a replacement. It is HAS been done, so is within the realm of an amateur constructor, but serious dedication is a must.
And of course there is the joy of making a burner that works efficiently, stays lit, doesn't coke up the flues, etc.
Steam engines seem simple, but when you actually start dealing with everything it takes to make one work internal combustion starts to look a lot more attractive. So much so that you can have a diesel engine burning oil that costs more than coal, running a generator which runs motors which turn the wheels and the railroads find the cost of operation much lower than steam engines.
But please take all of this as a challenge, do it, and take lots of video for me to drool over!
