I ran across a web site a couple years ago. The guy fed the steam through a home made check valve, mounted in the spark plug hole. The valve was made of standard fittings & pipe with a spring & ball bearing inside. Then drilled and tapped a hole in the piston to mount a bolt, that would open the valve when the piston got close to TDC. Timing would be ajusted by either the bolt length or moving the valve in or out.

I don't remember what he did with the regular valve timing. But I would think you would have to rework the cam to get it to turn 1:1 with the crank shaft.

For one, the original camshaft would have to be removed and replaced with a custom desinged and fabricated one.

Remember, on a gasoline engine there are four distinct strokes, spread out over two revolutions of the crankshaft : Intake, Compression, Power, Exhaust.  Or for those that have had military training on the subject : Suck, Squeeze, Bang, Blow.

With steam, it is a two stroke system : Inject steam on power stroke, exhaust spent steam on the upstroke.

So to make a gasoline engine work on steam, the intake valve would no longer be used at all and the exhaust valve would have to be rigged to open on every upstroke.  I guess you could then use the exhaust lobe at a different time to activate the steam injection....

One other thing to consider is that most gasoline engines are used to having petroleum products spewing through them.  You start putting hot water through them and you're going to develop SEVERE rust fairly quickly.  You're also going to get miniscule amounts of blowby on the piston rings which will then mix with the oil.  And if you've ever had a blown head gasket, you know what happens when oil and water mix in a closed loop lubrication system!!

The best engine for conversion to steam is the Wankel rotary found in Mazda RX-7's.  You run the steam into the intake port, remove the first spark and use that as an exhaust port, then use a timing system to inject steam into the second sparkplug hole and the exhaust becomes the other exhaust port.  Then just duplicate the setup for the other rotor.  Viole'.  A double-acting, self starting, twin chambered steam turbine.  And since the rotary engine has no direct linkage between the combustion and lubrication, you don't have that worry.  And since they already use an oil injection system, lubrication of the steam areas is already supplied as well!!

Also I am geussing steam would be a smoother less violient power than exploding gas would be, less shock.
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nothing to lose