Chapter 4 “Does he really need all this equipment”
While all the packaging work was being done, I was also refining the cylinder head. Once I had got to the point where I knew that the design of the head would package and work within the Mini engine bay it was time to make the big decision:
Do I turn the intellectual exercise into a reality? Or leave it there. I know this may sound like there’s a lot of work to this point, why would I do this if I wasn’t planning to go all the way. Well the simple answer is that up until now I had not put a lot of cash into the project, to go to casting meant a commitment in money, with a chance of wasting a lot of cash that could be spent getting the 5 port going. But to be honest I had actually gone too far to back out and spend the rest of my life wondering…
During all the design process I had been planning how the head would be cast, there would be inlet and exhaust and water jacket cores. The outer mould would be made in three parts, a top, bottom and front piece. As I described earlier, I had modelled a machined head, now I had to re-model it with casting allowances included, as well as the feeder and vents. Casting allowance is 5 mm for all machined surfaces from this I could then model the cores and moulds directly.
That’s right I would model the moulds, no patterns would be made, yes you read that right I did not make patterns. Instead I had the moulds 3D printed in sand… This is one of the ways I kept costs reasonable and kept the pace up. There are a number of advantages to using this technique:
• It’s quick
• It’s very accurate
• Very reasonable price for one off and small volumes
• You don’t have to worry about draft angles and over hangs (indeed the water jacket would be very impossible to make in a single core box)
• It’s seriously cool!
Before I committed to this, I did 3D print a 40% model which I took to the foundry to discuss with the casting gurus there. This was very fortunate as I found that I couldn’t assemble the exhaust core through the water jacket core as I had thought I could. Result was I had to cut the water jacket into 2 pieces. Doh! Has to be said the foundry guys were awesome, spending time to help me and show me around, there wasn’t any issues with helping one dude with a single casting. And their Guru had been casting longer than I have been alive (and I’m 51).
Once I had the OK from them, I went to CSIRO in East Melbourne and they printed my first set of moulds. Again they couldn’t have been more helpful.
To explain these images, the head is cast upside down, however the mould is also assembled upside down… Normally the foundry wouldn’t do this as they don’t like to turn finished moulds over but as this was only a small one they were OK with it (They showed me a flywheel they had just cast at over a tonne, so an 18Kg casting is tiny!)
Attachment:
Mould Slide1.JPG
Attachment:
Mould Slide2.JPG
I haven’t got any images of the thermostat housing or inlet manifold moulds, they were simple 2 piece moulds, with one core…
Once printed I took them to the foundry who cast them:
Attachment:
Head Slide1.JPG
Attachment:
Head Slide2.JPG
Attachment:
Ally Slide1.JPG
Attachment:
Ally Slide2.JPG
If you look at the top (bottom) face of the head casting you can see it’s a bit rough, this was the only area of concern, the rest of the casting was perfect. I can tell you this was a tense time for me, once I had the casting though I was on a bit of a high for a few days. I wanted to have 2 initial heads cast so after the first success I added an extra 3 mm. of allowance onto the top of the casting due to the rough surface being a bit of a worry and had a second mould made.
This casting blew big time, I ended up with a huge hole in the middle. This was probably the lowest time during the whole thing, and I nearly threw the towel in. However I cut it up with an angle grinder and found an issue… When I added the 3mm of extra allowance I had to update the water jacket design to match… I had the wrong water jacket! This meant that it was not touching the top of the mould so couldn’t vent properly, I now knew why the casting had blown! The printers printed me a new set of moulds and the foundry made the casting, as slowly as possible to aid venting. This third casting looks perfect, I havn’t had any machining done on it yet though…
It’s off to machining now, but that’s another Chapter!
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