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.
« Last Edit: December 20, 2013, 04:55:05 pm by markb »
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