Topic: How Long Did Honda Sandcast the 750 Heads?

[Mikey G.]

I've been doing a bit of poking around for the answer myself, but I was curious if anyone knew if Honda sandcast the heads for the CB750 for a while after they stopped sandcasting the rest of the engine?  I've got a "vaguely-early-70s-ish" engine I'm rebuilding, and while the original top end came off a...

Well, the bike originally was a period chopper, titled as a '73 with a '72 frame, but K0 carburetors.  Engine was stamped as a '72, and the head has a number of features that peg it later than '69s for sure, but earlier than say a '74/'75.  Thing is, certain parts on that head look REAL sandcast to me.  Is there a good way to tell a sandcast head vs a die-cast one?

It's not really a question of value (my 750 is a hodge-podge of parts, and always will be), just a bit of a curiosity I had.  Thanks for indulging me!

[BenelliSEI]

If it’s a really early head, it will not have oil restrictors, but alloy plugs in the oil hole that feeds the cam box. They have a small hole drilled in them and are not easy to remove. Expand this photo and you will see what I mean.

[MauiK3]

Every time I think about the orifices I get the urge to go change oil…….again

[HondaMan]

The sandcast heads have no center-front 6mm bolt holding them to the cylinders. This changed at about engine #1007808, but some sandcast heads AND cylinders appeared on the early K0 bikes. These were recycled refugees in the Old Factory's scheme of doing things. Thus, NOT having that bolt doesn't positively ID it as a sandcast engine, just as a sandcast-era top-end part. I've seen both later heads on top of sandcast cylinders (with the bolt hole there in the head, not in the cylinders) and vice-versa, although I admit it's been more years ago than many members here have been riding...

[PeWe]

Heads were sandcasted a little longer, right? The production method.
With all holes and removeable oil orifice.

[HondaMan]

Yes, the top ends were cast in sand molds until the K4, which had the first of the injection-molded tops (the K2 got the first injection-molded bottom-end parts). The difference is instantly recognizable as the injection-molded versions have flatted edges on the fins. The sandcast molded versions used lost-wax casting techniques to flow the metal into their shapes. These wax models were made in molds of their own, into which molten wax was poured. We used to call this method "lost-wax casting", but it is almost nonexistant today.

[Mikey G.]

Okay, that makes sense.  My head it definitely not K0 early (in that it does have that front bolt hole), but the rough casting surfaces on the inside (under the cam towers, etc.) surprised me.  I guess I was under the impression that once the rest of the engine went to die-cast the heads did too, and since my "bike" (if you can call it that) has always been a revolving door of parts from various sources, I was curious if it had somehow snagged an early head somewhere along the way.  Still, it fits with the rough area that most of my parts fit in, sorta '71-'73 at the latest.

Thanks!