The International CBX Owners Association

I’ve just bought number 12 cbx1000 prototype. A friend of mine owns a foundry and seems to think the head is Sandcast as well as the block. Is there any way of me identifying this, the bike’s had quite a lot written about it in the past but I can’t find anything to confirm it has a cast head.

Number 12 Protoype was a complete bike located in Belgium at one point. There are people who claim that early pre-production/prototype bikes had sand-cast heads and engines. If that is true and at what point (number) Honda changed to die-cast is unknown/undocumented. Having extensive experience with aluminum castings from my former job, I could tell if the head and engine are sandcast if I see it in person or maybe a high resolution picture. Usually the surface is quite a bit "rougher", almost like "petrified" sand. At this point, it doesn't really matter. No 12 is rare enough as it is, sandcast or not shouldn't make a difference. Congratulations! Mel Watkins will be jealous!

All the heads were cast before machining, its just a question of how.

NobleHops wrote: ↑

Sun Oct 30, 2022 9:32 pm

All the heads were cast before machining, its just a question of how.

That’s a good point! I think sometimes people confuse Sand Casting with Gravity Die casting, the later a process the Japanese used long after most other countries had moved onto Pressure Die casting.

Congrats on the acquisition of #12! You are indeed in rare air. Some detailed pics would be great if you can swing it. It would be a chance for many here that do not know how different the pre-production bikes were to learn about them.

Dave

What does machining have to do with it? The head is only machined on the combustion chamber side and in the cam journals and bolt seats. The fins are raw casting surface. There are a variety of aluminum casting processes commonly in use. Sand casting is a "lost form" process with a sand core, then there is gravity die casting, where the molten alloy is poured through gravity into the die. The die is being re-used. Pressure die casting is a slightly more precise process with the vessel that contains the molten alloy is being pressurized and the medium is "shot" into the metal die. Finally, there is vacuum or squeeze casting, where the die is evacuated or pressurized to help the molten alloy fill small and tiny cavities for the final form. Depending on the amount of parts required and the precision of the casting needed, a process is selected. Almost all production motorcycle engine cases and heads are gravity die casting, using a multiple use die. Shot number is about 30-50K. With a nest of 4 dies, this will produce 120-200K parts before re-tooling is needed. The die for pressure die casting and squeeze casting is made out of metal and provides 100K shots. Used for higher volume requirements and more precise shapes. Biggest drawback of squeeze casting is the longer time it takes to produce a part. It does eliminate the downside of gravity and pressure die casting which is porosity of the final part which can cause "seeping" through the walls if used in a pressurized part (hydraulic pumps). A couple of varieties, like investment die casting, exist.
Years ago, there was a member here from NJ who was heavily involved in the CB750K. I met him once at Mid-Ohio and he had a CB750K motor in his truck that he had medium blasted on the outside to resemble sand-casting. We all know what the significance of a sand-cast motor in the CB750K is. Of course, the serial number what tell the true story.
I have evidence of CBX No 37 still being sand-cast, so No 12 sure is also. Here are a couple of pictures of CBX No 12