Two Barrel Carburetor

Discussion in 'Lost foam casting' started by Al2O3, Dec 28, 2019.

  1. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    The great thing about finishing up a project is getting to start another one……though sometimes I don’t let finishing the previous project get in the way of starting a new one!:D

    Well it’s really half of an Inline Carb 4 barrel like this one

    1 Inilne Carb.JPG

    When I got this one it had already been cut in half. Here are the castings from half an original carb.

    1.1 Castings.JPG 2 castings.JPG

    It makes for a big 2Brl at 2.25 bore. The Inline Carbs are collector’s items and too valuable to cut up so I figure I’ll just make the castings because I’ve already reproduced just about every other part for them. This will be part of a bigger project that will include an intake manifold casting project too. More on that later. On to tooling up the carby castings. I’m planning to make a dozen sets.

    So my usual pin router patterns. So far I’ve made the Throttle Body and Main Well. I took some liberties, simplified features and added stock for castability and machine stock.

    3 Templates.JPG

    Here’s how the Throttle Body turned out….

    5 With Casting.JPG 6 WithCasting.JPG 7 Foam TBody.JPG 8 Foam TBody.JPG

    ……and the Main Well.

    9 MW Casting.JPG 10 MW Casting.JPG 11 MW Casting.JPG 12 Main Well.JPG 13 Main Well.JPG 14 Main Well.JPG

    I still have the Air Horn template to make…….the Main Well was the most complex and the Throttle Body the easiest. The Air Horn will be a tweener.

    More to come.

    Tobho Mott likes this.
  2. What do you do for a challenge Kelly?... an 8 speed automatic transmission? :cool:

  3. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    ;) It can seem a bit unnatural to see some of the shapes in foam......but also satisfying and even more so when they become useful metal parts. It's just great to be able to train metal into place. As far as challenge, an acquaintance of mine who asked for 6 of these carbs, built a V12 Ford small block from two V8s and has stuffed it into a GT40 chassis. Now if he can do that, I figure what's a few carbys?.......BTW, he's signed up to machine all the castings with additional sets due to me in exchange for the castings.

    Those automatic transmission circuits are sort of the ultimate in a hydraulic manifold. I've always been more of a manual tranny guy but admittedly, the dual clutch trannys with flipper shifting are fun. With a good scan and a CNC router, that could be done practically as a one-off in foam. On the other hand, if you could do all that, why not machine directly from plate........unless you are making many 1000s.

    Last edited: Dec 31, 2019
  4. Tobho Mott

    Tobho Mott Silver Banner Member

    MUST you always make it look so easy!?


    J/K, great work!

  5. Peedee

    Peedee Silver

    I was just going to like that comment Jeff, but I'm going all out and saying my apron is well and truly hung up as I haven't a hope of doing what kelly does with this stuff!
  6. ESC

    ESC Silver Banner Member

    Way to go Kelly. What is the plan for material? The originals were probably die cast. I wonder if the pouring temps would be high enough to completely fill the mold?
  7. DavidF

    DavidF Administrator Staff Member Banner Member

    I was wondering how long it would be before you attempted the carbs....
    Are you making the float "Ears" (where the floats pivot pin goes) a bolt in ??
  8. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I didn’t manage to get out in the shop until early afternoon today but got the Air Horn most of the way there.

    Air Horn Templates made.

    15 AHorn Templates.JPG

    I’ll need to make a fixture to center the booster and leg when I glue them in place…..I’ve got a plan…… but here’s the Air Horn so far:

    16 Horn Casting.JPG 17 Horn Casting.JPG 18 Air Horn.JPG 19 Air Horn.JPG

    ….and the three together:

    20 Three Patterns.JPG 21 Assembled.JPG 22 Assembled.JPG

    -Getting there.

  9. rocco

    rocco Silver

    Stunning! I never would have believed that level of repeatable precision would be possible without CNC. We've seen you use your overarm router in several videos, I hope some day you'll find the time to make a detailed video about the router itself.
  10. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Thanks fellas. I did blow up a pattern and had to fix a couple small boo-boos bugging out the templates but they seem to do the job.

    I built in shrink for aluminum but I also have some Zamak 3 and the parts are small enough I doubt the shrink difference would matter. Don't want to jinx myself but feel pretty good about them. The originals were gravity fed permanent mold (Tippers) and were actually aluminum. Not sure what alloy but it welds very nicely......I've repaired many of them. There's some period production line photos here:

    The typical wall is 3/16" thick (the originals were 1/8") but there are some massive sections where I intend to gate into. I think I'll get them to fill. If not I'm sure vacuum assist will get me there but don't think I'll need it.

    Good eye David. I'm going to glue those on. The finished main wells are just under 2" tall and to include them, and since I only have 2" thick foam board, I would have had to machine through a glue joint which usually doesn't go well so I just decided to glue the ears on. The inward surfaces of the ears will be as cast and outer get machined as the ears tuck up into the air horn casting. I added material such that all the original parts and gaskets will interchange but they'll be a little heavier and a reasonable facsimile of the originals but no attempt at exact copy.

  11. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Thanks rocco. I have a small confession.....I've used the DRO on my mill to do the lay out work....any where you see a dowel pin, that was done with NC accuracy as are some of the critical features.......but cutting the foam patterns on the pin router is quite repeatable. I only just started using my DRO to do lay out work. Up until this project it's all been pencil and ruler.

    Well it's not a video but I did do a write up on it over at AA and since I uploaded the pictures to AA, it still lives.

    I stopped going into much detail about my pin router because I didn't think anyone really cared and all in good fun proceed to take the piss out of me for not building a CNC router.....which I want but until then I'm getting by.

  12. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Finished up the Air Horn this afternoon. I started with the booster body. The booster OD is 1” which conveniently is the size of my largest plug cutter. I bored a one inch hole in a chunk of wood, slit it, centered it under the Forstener bit, clamped the jig to the drill press table, clamped the foam plug in the jig, and drilled it with a smaller Forstener bit.

    23 Booster Jig.JPG

    I tried both ¾” and 5/8” for 1/8 and 3/16” wall respectively. I was pleasantly surprised with how well it worked.

    24 Boosters.JPG

    I was eyeing them up and thought the thicker walled booster would be much more likely to fill, and I’m probably inviting a fail, but decided to run both thin walled boosters. They are actually only .100” wall. Probably should have used one of each on this first test piece.

    25 Booster Wall.JPG

    So I made myself an assembly fixture and bored the holes for locating posts that position the booster bodies, and made discs to center the Air Horn. I tuned up the post diameters with one layer of aluminum tape for a nice fit.

    26 Milling Assy Jig.JPG

    The three spokes on each booster are additional supports and perhaps gates that will be machined off. The fourth contoured piece is the down leg that mounts and feeds the booster fuel.

    27 Jig.JPG 28 Jig.JPG

    Finished it up with a little wax filleting around the boost leg and bosses.

    29 Detailed.JPG 30 Detailed.JPG

    Sprued/gated into the most massive part which also happens to be adjacent to the booster down leg so at least that booster should see some hot metal.

    31 Sprued.JPG

    Dipped it. I’ll let it dry over night and with any luck have at it tomorrow. I think to have any chance I’ll have to use vacuum. We’ll see.

    32 Dipped.JPG

    Tobho Mott and Mark's castings like this.
  13. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Poured the Air Horn this morning.

    Here’s the coated and dried pattern ready for the mold.

    33 dried AHorn.JPG

    Here it is straight out of the sand and quenching bucket. It must have had a sufficient level of pre-pour doubt because it's a complete casting including the thin walled boosters!

    34 As Cast.JPG

    I did use vacuum assist…….about 7”Hg so in addition to the head from sprue height, the vacuum added an additional ~3.5psi of head pressure. When I use vacuum with one thin coat of refractory coating, I often get these metal penetration flaws where the molten metal penetrates the coating and infiltrates the coarse sand mold media. I think I may be able to prevent this by applying a second dip coating of refractory. Having poured this, I'm also much more optimistic about casting the part just as gravity fed without vacuum.

    35 Boogers.JPG 36 Boogers.JPG

    The strange thing is, there is still a thin refractory coating between the casting and the flaw at the pattern boundary, and if I slip a sharp wood chisel under the edge of penetration booger, they pop right off. Here is the same casting after 2-3 minutes of hand work.

    37 DeBoogered.JPG 38 DeBoogered.JPG

    …..and here it is a few minutes later after a brief visit to the media blasting cabinet. I left the booster supports in place to keep the booster stable later during machining.

    39 Cleaned Up.JPG 40 Cleaned up.JPG 41Cleaned UP.JPG

    Well that was so fun I figured I may as well get the Throttle Body and Main Well ready to pour.

    42 Throttlebody Sprued.JPG 43 Main WellSprued.JPG 44 Both Dipped.JPG

    I think I’m going to ring in the New Year tomorrow with two more new castings!!

    Mark's castings and Tobho Mott like this.
  14. That's very impressive, I have almost a mental block about copying detailed diecast objects but such a complex shape is an ideal use for the lost foam technique. Is there some coating you could paint the polystyrene with to level the surface?. Almost anything that is solvent thinnable is going to dissolve the polystyrene so some of the waxes I use that can be thinned with petroleum spirits are out of the question. I wonder if linseed oil would coat it and then burn out on contact with hot metal?.
  15. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Thanks Mark. A self leveling dip that burned out ultraclean and didn't attack Polystyrene would be quite the trick. As near as I can tell it would need to be something soluble in water or Alcohol (or?). I've used shellac for glue but it doesn't burn out clean. Ever look up what shellac actually is? It's surprising.

    I wipe Carnuba wax (good ole paste wax) on PS foam molds for release agent all the time and it doesn't seem to attack the foam at all. I think with many coats and cloth buffing you could build up a luster but not practical for complex shapes and surfaces......I'd be open to suggestions.

    It needs to be something in suspension that dries or reacts because temperature curing is basically out with PS.

  16. Shellac?, the excretions of the Lac beetle. I'm using some old lens blocking wax (to mask aluminium for etching) which is used to mount plastic lens blanks to aluminium bases before they get machined, ground and polished. I'm not sure of the composition but I suspect it's low melting point polystyrene "wax", at any rate it's expensive stuff. The blue lens wax melts at 95 deg F and may be too thick, also further down the page is a water soluble wax product.
  17. rocco

    rocco Silver

    I wonder how PVA mold release would work? I've used on foam before although not for casting. It doesn't affect foam at all, it's readily available, it's fairly cheap, it's easy to spray on in a thin even layer, it dries quickly to form a thin film, if it burns out well, it might fit the bill.
  18. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    .....and I have a gallon! That's brilliant Rocco. It's commonly used as a barrier coating for release agents so you might be able to dip or spray PVA and then apply something else that has solvent like paraffin's. The only potential is rapidly reduced by water so no water based top coats without another layer of water barrier.

    Might have to experiment a little with that.

  19. rocco

    rocco Silver

    A little off topic but, I've used PVA over foam then glassed over the foam with polyester resin normally,polyester resin on foam would be a recipe for disaster but a couple coats of PVA provided adequate protection for foam. I used that method to make this air filter housing, you might call this lost foam of a different sort.

    Air filter housing.jpg
    Last edited: Dec 31, 2019
  20. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Poured the Throttle Body and Main Well today.

    Here they are ready to go.

    45 Dried.JPG

    The Main Well came out great.

    47 MainWell.JPG 48 Main Well.jpg 49 Main WellClean.JPG

    The Throttle Body poured short….way short…..:mad::(

    50 TBody Short.JPG

    First fail I’ve had in a long time. I poured both from the same heat and the TBody was the second. It was cold outside and am sure I lost some heat, but with the combination of the very long gate and short sprue/low head pressure it wasn’t even close. Funny because I thought the TBody was the easiest of the three. Mercifully, it’s certainly the easiest pattern to make of the three.

    So I did what any self-respecting caster would do, marched straight to my pin router and made another pattern.

    51 New TBody.JPG

    Lengthened the sprue, shortened the gate, and contacted more centrally.

    52 New TBody Sprue.JPG

    and dipped it

    53 New TBody Dip.JPG

    We shall try again....Happy New Year all.


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