TOP HEAD MOLD

If you have dial up let me apologize up front for the image heavy page! 

Although it would have been much easier to sand cast this part I chose to do it the hard way once again. At least this way every part will be the same and it will save me a lot of machining. For instance, the combustion chamber presents something dreadful to make repetitively on my non-CNC equipment. The fins which follow the contour of the combustion chamber would have been an equal pain not to mention the cost of buying a few tapered end mills. (For this much work I'd surely break a few)

My goal is to have at least fourteen sets of heads made up so that spares won't be an issue for a while.

Not counting my time this mold cost roughly $50.00 including grinding wheels, etc. After making the sub head mold and having learned from several bad castings I took the experience and applied it to this mold. The first casting didn't go well because I didn't melt enough metal. There was no mold preheat on this pour so the fins were chilling shut before they filled.  The second casting was a bit shy of having as much aluminum as the mold could hold but due to preheating the mold and a lot of acetylene soot on the mold it went very well.  Something tells me that the third pour will be a winner.

The most surprising difference noted on this mold was how well the fins dropped out of the casting. After letting the casting set for 4-5 minutes I removed it from the mold and everything fell out/off of it.

In synopsis, the things that make using a permanent mold easier are...

1.Mold preheat

2.Mold release (acetylene soot)

3.A choke in the gating

4.Decent sized risers/feeders

5.Polished surfaces with at least a 2.5 degree draft (taper)

6.Removal of mold components while the casting is hot hot hot. (With good gloves and protection of course)

Here's the mold prior to the first pour.

Making the combustion chamber was pretty easy... Much easier than machining it every in every top head blank.

Above is a picture of a fin having a taper machined on it. Note the 1/16" welding rod used to prop it up for the face mill. Actually the bar shown was long enough to make two fins. This went much easier than grinding a taper in. A 1/8 diameter rod was used when it was flipped.

The fins then had the contours of the combustion chamber cut out of them. Each fin was then stamped with a number. The bolt pattern matches the final bolt pattern but the real reason for having the holes was for ejection from the mold. Fortunately everything falls out of the mold.

The fins are completely separate and are spaced with 1/4" key stock. Six 1/4-20 bolts keep them in position. This makes removal of the casting much easier should something get "hung up".