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Lost Foam Casting: a Crankcase in Zinc Alloy

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vtsteam:
Since I got my Popular Mechanics boiler steaming I really wanted to make a new small steam engine to go with it. I especially like twins, and have a couple Westinghouse style versions. I was just thinking of a V-twin this time, instead of an inline,  and with OKTomT doing a really nice full size IC V twin motor bicycle engine, I wondered if I could use a similar crankcase on a steam design. So I started in on what I hope will be a lost foam casting.

I say hope because this one really may not work out well. One reason is, it's very thin walled and it's going to be tough to get full penetration of the metal. The other is, I'm going to try lost foam with zinc diecast metal instead of aluminum, which I've used before. The lower pour temperature of this metal (by nearly a third )may not burn out the foam. So all in all, my hopes aren't great for this working out. Still, you never know until you try, and it's definitely something I wanted to satisfy my curiosity about. If it doesn't work, I can always try a hotter metal.

Here is the foam crankcase as of yesterday:

vtsteam:
I added bearing bosses and sprues today, and then plastered the patterns. Here's how it looks tonight:

Manxmodder:
Hi Steve, this looks like it will be an interesting experiment.
Just to add something I have been thinking for a while,if the foam is a polystyrene type then the majority of it could be dissolved out of the mold by introducing cellulose thinner to the foam core.

Then apply some heat to drive out the solvent residue. How do reckon that would work?....OZ.

vtsteam:
It's been done that way Oz. But it would need a thicker more supportive investment, and maybe heat, etc. to drive off the moisture, solvent and residues. It gets to be more like lost wax casting -- quite intensive

This way is, I believe quicker and simpler (well only if it works!). I hope to cast tomorrow, and we'll know pretty quickly!

I've cast this way before with aluminum and a larger thicker walled casting:

Manxmodder:
Very impressive Steve,that has replicated the detail very well.I'm taking notes on this one...OZ.

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