[basjoos]

One of the main problems in converting an internal combustion engine to steam is the totally opposite approaches that steam and IC engines take toward heat loss from the cylinders. In a IC engine combustion is taking place in the cylinders, so they are designed to extract heat from the cylinder walls to keep the cylinders from overheating. But with a steam engine, combustion takes place away from the cylinders and, since any heat loss from the cylinder wall reduces engine efficiency, they are designed to minimize heat loss from the cylinder walls. So as as a minimum, you are going to need to get rid of the air cooled engine's cooling fins and insulate the cylinders to hold in the steam's heat as it enters and is expanded in the cylinders.

Its hard to build a very efficient steam engine from an IC engine because of this excessive heat loss and the single cylinder size makes it difficult to impliment the multiple (douple, triple, or quadruple) expansion cylinder sequence that is needed to produce an efficient steam engine. Each subsequent expansion step needs a piston of larger surface area to utilize the lowered steam pressure of each steam expansion.