SOHC.co.uk Forums > CB750
Petrol tank chrome strip .
MCTID:
Well I certainly don't profess to be an expert or even that experienced in the various casting techniques, but I have worked with a variety of cast products in my past and I do recall that when Pressure Die Casting was introduced to the motor (motorcycle) industry, it offered many improvements over Sandcast products.
The much higher costs associated with Die Casting Tooling was recouped when high volume production runs were envisaged and it's likely that in the early days of the CB750, the need to get the model into production (to be the first high volume Manufacturer to bring a 4 cylinder bike at an affordable price into a highly competitive market) and to keep unit costs down, was probably why Honda initially used the Sandcasting process. No doubt, Honda also expected that once the model was in production, minor changes to the crankcases (and the moulds) would be needed to improve the design, make the quality of the castings better and to ensure they could be accurately repeated with minimal scrap. Once production runs start, the Foundry often asks for modifications to be made by the Designer to assist the Casting process, improve repeatability or to reduce the scrappage rate. Some Designs are great on paper, but cannot be achieved cost effectively using a particular Casting process.
Once the CB750 was released and Honda was assured of high volume sales, the enormous set up costs of Die Casting moulds could then be justified and that's the way they went from then on.
One of the main difficulties with Sandcasting is getting the molten material to flow and to cool uniformly - especially where cross sections change and sharp corners exist......and the CB750 has plenty of those to contend with. I'm not sure what the reject rate would be at that time, but it can be a major problem when you have completed most of the expensive machining only to discover that your casting has air pockets, voids where the metal hasn't formed properly or has trapped sand inclusions and has to be scrapped. If Honda subcontracted the casting process to others, their dilemma would be that Honda would only pay for 'good' castings with scrap being returned to the Foundry for a FOC replacement - not a good way to make a profit.
The huge costs of manufacturing Die Casting Moulds and the associated equipment is often offset with a deal struck between the Foundry and the Client with one party 'owning' it and the other paying for each casting produced, or amortizing the costs over the life of the tooling with lump sums paid at agreed milestones. I would imagine that Honda probably owned or bought the tooling to maintain control and they would most likely have had a number of moulds in use at any given time, and therefore be able to switch production to different Foundries as they chose. These same principles would apply if Honda kept the whole process 'in house' as each department would be treated as a business which needed to show a profit at the end of the day.
Although Sand Casting equipment is much cheaper to make (and easy to modify) the casting which is produced will invariably suffer from porosity and differences in wall thickness, and often such defects will not be apparent until it fails in service - at great cost to Honda (reputation as well as financial) so there is little doubt that as soon as Honda had settled on a Design and a manufacturing process, Die Casting would have been an ideal method to consistently give them the high quality and cost effective components which they built their business on. I have just had my K4 engine in pieces and I have to say that the quality of the complex crankcases some 40 years later is astonishingly good and makes my other bikes (Triumph) of the same era look almost 'agricultural'.
royhall:
You didn't mention labour costs Alan. Once the die casting tools are made, the labour costs per casting plummet.
That's why I could never understand why the British bike industry never got past Sandcasting when they made virtually the same product for several thousand years.
Porosity can be a factor in Sandcasting as found by the Brit bikes and is well documented. Some still leak no matter how well they are built.
AshimotoK0:
--- Quote from: Oddjob on March 30, 2016, 01:24:31 AM ---Yes Ash please stop vomiting all this 750 info, it's boring the pants off us 500 fellas :) :) :)
On another note, stopped at my local Honda dealers today and was speaking to my mate who is still in the trade, used to work with him at Queenies. He said something that TBH surprised me but may not you. I mentioned the DS video on facebook? and the hysteria around 750 sandcasts which TBH I can never understand and he said the sandcasts suffer with porous crankcases and was one of the reasons that Honda went to die cast cases. Never heard that before (but then never was interested in the 750s enough to discuss them) any idea if that's true or just one of those urban myths.
--- End quote ---
Honda coated those sandcast cases inside with some kind of sealant I think. Should have asked that guy from Queenies if the new out of the crate from an auction CB500/4 in Manchester that turned up in York was from there ... instead of discussing sandcasts yaaaaaaaawn Ken ;D ;D BTW I am a 500 fella myself now!
Good job they removed that black stripe on the K0 anyway to allow us restorers to use good old BL Mini trim ;)
MrDavo:
While we are on the subject (ish) has anyone got a new or vgc left hand K1 strip for sale? Will pay cash or swap for a pair of VGC K0 ones.
I could mask and paint black stripes on mine, OK until the paint starts to chip or flake around the edges. ???
atlsec:
Hi Guys ,
This is all interesting stuff and I`m sure most of it is correct but on the cover of The Motor Cyclist April 1969 it shows a sandcast which they road tested and that has the black stripe strip on it .I cannot see that that magazine would get a prototype model for testing . Also someone said that Honda did not sell complete engines ,Why not .And due to the fact that a lot were destroyed in the early days of production I do not believe they were rebuilt .I believe they got new engines from Honda . I would not trust many people to rebuild an engine ,especially main dealers .
Cheers , Alan .
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