1930-ish Austin Seven half size engine

Discussion in 'Metal casting projects' started by Lee in Cornwall, Sep 1, 2021.

  1. I am hoping to post some pictures of my project soon. I am in the process of buiding a half size working model of an Austin 7 engine. I have cast two small parts for the engine and they have come out reasonably well. But I always turn to the big parts and wonder how to cast them. The A7 engine has a separate block and crankcase. The block is cast iron, the crankcase aluminium. I am going to use aluminium for the block and head because I don't have the ability to melt iron. The block will require cast iron cylinder liners. I have 3D printed the block so I would have a physical object to examine. There are so many areas that should have draft that I thought it would be almost impossible to do at home. But, thanks to watching many youtubers videos I have a cunning plan. I will produce a new 3D print with no draft and take a rubber mould from it. I will then use the rubber mould to either produce a wax pattern or an easy to melt metal (pewter?) pattern. This pattern will then have some kind of investment shell and when fully set, the pattern can be melted out. I can then use the shell to produce an aluminium casting with no draft. I hope to learn more from this site to see if I am on the right track. I will try casting the cylinder head using greensand, but there is no draft on the pattern so it might not pull from the mould cleanly. Both the head and block also have a water core.
  2. dtsh

    dtsh Silver

    I haven't tried it myself, but some have had luck using thin walled prints and using them instead of foam for shell casting, might be something to consider.
    There's even a filament designed for the purpose, Polycast.
  3. Jason

    Jason Gold

    Hell, I had an austin 1098cc with a pair of su's, fully rebuilt and was gorgeous I gave away! Where were you 22years ago?
    It even had the gearbox on it.

    I would like to see your little creation. These engines were bulletproof.
  4. ESC

    ESC Silver Banner Member

    Lee, this is what it took for the V8. With your 3D modeling the core boxes would be a piece of cake. This was also a wet sleeve cylinder, but full water jacket head. Was the 7 and overhead valve, or flat head?

  5. Jason

    Jason Gold

  6. ESC

    ESC Silver Banner Member

    Gotcha. It would still need a water jacket although quite a bit simpler.
    In half scale, that would be a neat little runner.
  7. I did consider that possibility, but with the number of pours that can go wrong I didn't want to keep remaking the pattern. Aspecially if I make more than one engine.
  8. I can't even imagine the work in making a V8. When I first started this project I decide on 1/4 scale. When I looked at my drawings for 1/4 scale I realized it was beyond me, so I then went for 1/3 scale. That was set aside in favour of 1/2 scale. I think I can manage that. I do get sidetracked sometimes though. Back in the 50s you could buy an aftermarket overhead valve cylinder head. Backburner, backburner.
  9. Hi Jason. I have owned A7s for nearly 50 years, I have rebuilt and worked on many cars. I have numerous books on the 7. And your photo of an A7 block is the first time I realised that the 7 might have come with a painted block and head! Because I will be making my block and head in aluminium instead of cast iron, I have been racking whats left of my brains to come up with a way to paint the aluminium to make it look like cast iron. If they were painted in the first place my problem is solved. I feel a bit of research coming on. Thanks and thanks again!
    Jason likes this.
  10. oldironfarmer

    oldironfarmer Silver Banner Member

    Looks like a great project. I have some spray can paint which replicates cast iron pretty well, an engine paint. I'll try to get a picture.
  11. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    If you already have CAD models and ability to 3D print, I'd think you'd have to have a go at investment casting. The challenge will be keeping intricate core work in tact during burn out, the pour, and getting the mold free of debris afterward. Also removing investment from the core work may be tedious if you get there. I've had a number of people contact me about using lost foam method for blocks and cylinder heads. Would have to see the water jacket but the block looks like a relatively easy lost foam casting. Do you have a cnc router?

  12. Jason

    Jason Gold

    I dont know what you plan on doing with this little motor after you are done with it, but seems me the British Motor Heritage trust would have an interest in it and your project.
  13. I have watched several of your videos and lost foam is an option I am looking into. I had thought of using silicone rubber to make the mould and then pouring a two part foam into it. I have seen this done on youtube by a company called brick in the yard. The detail reproduced with the foam is impressive, and as you have shown, foam takes a ceramic coating. It's something worth exploring as the silicone rubber doesn't need to be heat resistant.
  14. To be honest I had never got past pressing the starter button stage! I would like to keep the first engine, but I have been asked by others if I intend making more than one.
  15. rocco

    rocco Silver

    Those two part foams are usually a polyurethane foam and its burn out characteristics are not suitable for lost foam casting.
  16. Thanks for that! I could have wasted time and money trying this out. That's another one ticked off the list.
  17. Peedee

    Peedee Silver

    Has anyone tried those spray foams in a burn out - investment process? I know they won't take to direct pour lost foam.

    Perhaps nothing to be gained over wax invested.
  18. I've just watched a youtube video with that process. Lots of fire and smoke and the finished part had lost some detail. I think wax may be the way to go.

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