After about 2 weeks of a aluminum welding fiasco, we cast another head and are back on the assembly and trial phase.
The casting came off significantly better then our last casting - still had a few gas voids but nothing like the first, the process has improved greatly.
Couple of photos from the casting - primarily difference was two fold - first we used a lot more vents for the foam gassing. The only gas voids we did get were from flat areas where the geometry trapped the gas from venting. Every top suface must be vented. The second improvement was to use some green sand for the interior fins to better combat gravity of the sand wanting to drop out prior to pour.
Here in the first photo we have the model coated and vented - using the drywall slury, you can't see them all but there are 5 vents in addition to the sprue on the top side of the model (this is the orientation of the model during the pour)
The next photo is our casting set up - yes it cold out in Michigan in January - Looks a little redneck, but no problem doing a 40 lb pour with this setup. Foundry is in the foreground and casting pit in the back ground - a wash tub does the trick here - with the model coated we use primarily play sand for fill. We did use some green sand for the interior fin slots but not much.
Here is the part right out of the sand, looks a little rough but not bad. The snow did add a bit of mystery to pour - misting looks like the gates of hell.
Here you can see a comparison of our first head pour and then the current part. Big difference - on the first part we spent at least 8 hours of machining time - figuring out the best way to clean up the interior fins. On this last part, total machining time was about 2 hrs -
Back to engine assembly - more updates to follow.