Sandcast engine casting process - permanent mold casting or cast in sand?

[markb]

I searched because I thought the answer should be here somewhere but I couldn't find anything.  There is a discussion going on the SOHC4 site.  I said (and I may be wrong) that the process was permanent mold casting but there are some postings with sources that contradict that.  Anyone have a definitive source? 

[Steve Swan]

Good question.  i've not ever heard a definite answer.  permanent mold would be expensive, a metal case and sand cores would be involved and expensive to produce; as i understand permanent molds, not used for limited production runs.  Sand molded casting requiring a pattern, would not be as expensive and used for limited production runs.  Perhaps Vic World would know.

[kenhan]

According to John Wyatts book Original Honda cb750, he says at page 26 : " The first 7114 engines built had crankcases that were gravity die-cast, as opposed to pressure die-casting of all later sohc variants".
I don´t know what gravity die-cast means or how it´s differ from permanent mold casting, but thats my contribution to the "debate".
/Ken

[Steve Swan]

Would be good if John Wyatt had substantiated where he obtained information about casting technique.  Beautiful book, good resource overview for general vin details 69-78, not exhaustive nor completely accurate in terms of 1-7414 distinctions nor mention of the French sandcasts.  I'm not sure he ever intended his fine book to be a complete work of all things unique to the sandcast.   We have learned much since his book came out in 1998 and are still learning much.  Doubt we'll ever learn it all in our lifetime !

[kp]

My thoughts are that the term gravity die casting is probably incorrect as sand casting does not utilise a die rather the shape is achieved using a sand box mould. I suspect the answer can be easily googled but I lived in a place that had a foundry and did get to see how traditional sand casting is done The process involves packing sand around a pair of pre made moulds which are housed in boxes. In the case of an engine case you have an outer box mould and an inner box mould. Once the casting sand is loaded the mould is removed from both boxes and what you are left with is the outer and inner shape of the engine case formed in the sand. The boxes are clamped together ready for the molten alloy to be poured through a purpose designed orafice. Once cooled the two boxes are separated and the sand removed by vibration leaving a raw casting which is then ready for machining. The process is fairly simple and is still the preferred casting process for low production runs or where complex shapes are to be cast. A brass water tap is generally cast using this sand process. Sand is used as it can be easily removed from the raw casting. Specific types of sand are used and when mixed with other binding agents creates a durable and robust mould. The alloy used in sand casting is generally the purest form of aluminium whereas die casting alloy is mixed with zinc and other metals to aid in flow and part removal from the die etc etc etc. die cast parts are bitches to weld and in some case defy welding at all
Interestingly there are many Honda sandcast engine cases Early CBX, early CB1100R to name a few.
Hope this adds some info to the topic and welcome further posts on the subject

[kmb69]

This is a copy of a post I made on the SOHC Forum.

Quote from: Ujeni on December 18, 2013, 05:15:25 PM

http://www.sohc4.net/cb750-sandcast/
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Quote from: Powderman on December 18, 2013, 07:49:01 PM

I think the provided links have  made it clear they were never cast in sand molds.
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I respectfully disagree.

There are multiple incorrect declarations made in this reference such as, "The clutch cover is held on with 10 screws – the diecast engines have 11."
The Sandcast has 9 where the diecast/permanent mold has 10. Also not too sure about "The first thousand bikes were hand built, mostly in California..."
Never heard that before and believe it to be wrong. I am old, worked as a mechanic at Pasadena Honda when the very first ones arrived in crates from Japan.
While I do not consider myself an expert on the matter and am learning new stuff daily, I currently own 20 Sandcast 750's with VIN's ranging from 33 to 7083.
VIN 7083 was manufactured in Japan in 9/69 so certainly would NOT "...have been registered prior to August 1969."

I think Vic's article is more right than wrong and the SOHC article is more wrong than right. Many of the early engine parts, head, cylinders, and cases, are sandcast.
SAND CORES were used even with some of the permanent mold / diecast parts. Use a borescope to peer in the cavities under where the cam towers sit on a '78 K or F.
Got any ideas how they would get a "permanent / diecast mold" out of there?

Many of the early smaller parts were permanent mold and/or diecast from day 1, for example most of the engine covers. Others were sandcast such as oil pump bodies.

Maserati and Ferrari use the sandcasting method today on some of their blocks and cylinder heads. The molds are meticulously prepared with multiple patterns using robots!

My 2 cents. 

[kmb69]

This is a copy of the second post I made on the SOHC Forum.

Quote from: Ujeni on Today at 09:54:05 AM
....Hope you will chime in over at SOOC!
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I am on the SOOC, same handle. I had responded here before I read Mark's post on SOOC.

There are several reasons why I believe the Sandcasts were cast in sand molds. In 1970-1973, we were racing a laydown dragbike with a Sandcast motor. As we were machining the cases and cylinders for big sleeves, we found a few inclusions in the castings that contained sand. It is possible that it came from a sand core commonly used in permanent molds that was disturbed during the pour. But, I have just seen enough variation in the cases to make me believe they were cast in sand. If you look closely at early cylinders and heads, you will see differences in the mold parting lines where they were subsequently hand ground to get a reasonable match. There is quite a difference in surface finishes on the cases that I don't believe you would get from permanent molds. But to one of Mark's points, 7,500 is a good estimate for the life of a permanent mold today. Sandcast molds and permanent molds are both typically "gravity fed" so that doesn't really distinguish anything. I think permanent molds were used for some of the early engine covers because you can see a sanded brush finish on them under the clear coat as compared to today's diecast covers that are only machined on mating surfaces and holes and are very smooth. Compare the inside surface finish of the early covers to the surface finish on cases, cylinders, and heads. I think that demonstrates the difference you get in surface finish between permanent and sand molds.

Honda was not the company in 1968 that it is now and producing the CB750 was a pretty big risk from a business standpoint. They had to minimize cost until it was clear they had a winner. 7,414 bikes represents approximately $11+ million in sales at retail. I don't know what the dealer cost was but something less. Permanent molds would have represented a big investment in time and money as tooling was mostly manufactured on manual machines at the time.

Obviously, I was not a witness at the foundries but there is enough residual evidence to make me believe they were actually cast in sand molds.

[markb]

I figured if anyone would know it would be Vic World so I sent him a note.  Here's his reply.

Hi Mark,
 
I am not on the Forum, but you can add this if you like:
(Thanks, Vic)
 
There was a large coffee table book that came out  in the 1980s, that was all about GP race bikes from the early 1960s (no, I don't have a copy).....
In it were several pages full of photographs of exactly how molds (and especially cores) were made to produce those "one off" engines that Honda employed to dominate the GP races back then.
(at the time, Honda used 4 cylinder, 5 cylinder, and of course the famous 6 cylinder (RC166) engines to achieve their desired result...winning).
 
As those race engines were typically only campaigned for one year (sometimes two), not many engines had to be produced for the entire race season, so...they were sandcast (yes in sand "boxes").
 
But there was much more to it than that. What that book showed, was that in order to produce one engine, there needed to be some 20 (or more) individual sand "cores" made. These cores are "simply" blocks of sand (held together with a binding "glue") that are in the reverse shape of fins, (and the reverse of course) shape of other intricate components that it took to cast an engine case/cylinder...and head.
 
In fact, many of Honda's GP race engines actually employed casting the cylinder section all as one piece with the engine case! (this helped insure that those 18,000 RPM motors would have the crankshaft, rods, and pistons all running in exactly the same direction).
So for example, the cylinder head would require 3 or 4 fin cores (sliced vertically) to complete the left side of the head, and of course the same qty. cores for the right side...and then several more cores for the front and back. It's quite something to see a block of sand the size of your hand with 12 or 15 perfectly shaped fins.
 
(By the way, the 750 Honda achieved those finned combustion chamber domes Inside each cast head (directly under the cam towers), simply by using these same type sand cores).
 
Then of course all these cores were placed in the "sand boxes", the 2 halves were (carefully) put together, some sprues and breathers cored, and then the aluminum was poured.
When cooled, they simply broke out all the sand (including those intricate fin cores they just made!)..
 
So, some 7 or 8 years later when it came time to produce the 750 Honda, sandcasting the cases, heads, and cylinders was by then a walk in the park!
 
And yes, the valve cover, transmission cover, clutch cover, and alternator cover were all diecast (or sometimes called "permanent mold") from the start!
 
Hope this helps!
 
Thanks much for listening,
 
Vic

I'm a believer.  I'm going with sandcast.