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Gipsy manifold material

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David K19/01/2020 15:32:27
211 forum posts
152 photos

According to my plans the inlet manifold should be made of mild steel.

looking at a couple of completed engines on the internet I notice one has used brass and another has used a mixture of brass and steel as the one pictured below.

Is there any reason for using brass , as in the bottom plate on this one,

gyp11.jpg

old mart19/01/2020 15:34:58
1085 forum posts
113 photos

It looks pretty.

JasonB19/01/2020 16:05:52
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And it does not show the silver solder joint

Steviegtr19/01/2020 16:13:46
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469 forum posts
126 photos

WOW. Very nice.

David K19/01/2020 19:25:39
211 forum posts
152 photos

Stainless it is then.

JasonB19/01/2020 19:33:44
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I think if I were doing it I would machine some stock down to 0.475" and then mill out the recess from below to 0.425" deep and then recess the bottom plate into the 3/8" wide passage so no joints are visible unless you are looking from underneath.

Andrew Johnston19/01/2020 19:41:42
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Depends on which engine, but on the Gipsy Major the inlet manifold was steel. It has two half pressings with a welded seam and individual steel plates welded on that bolted to the cylinder heads.

Andrew

Tim Stevens20/01/2020 18:19:24
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1123 forum posts

Brass has an expansion coefficient very close to that for Al alloys. The value for Steel is rather less. I suspect this might have been one factor in the mind of the bloke what made it.

Cheers, Tim

Paul Kemp21/01/2020 00:45:41
376 forum posts
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Posted by Tim Stevens on 20/01/2020 18:19:24:

Brass has an expansion coefficient very close to that for Al alloys. The value for Steel is rather less. I suspect this might have been one factor in the mind of the bloke what made it.

Cheers, Tim

Not sure I follow your thinking there? Steel top, brass bottom, sounds like a recipe for a banana to me? As it's the inlet manifold would it actually get hot enough over its length to make any appreciable difference? If it were the exhaust a different story maybe. If you are suggesting coef of ex to match the aluminium crankcase then that only holds good if the whole thing is brass?

Paul.

JasonB21/01/2020 07:14:01
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The lower tapered part down to the carb is aluminium but at such a small size I doubt expansion would be an issue and the suggested Araldite to join it would have enough flex to compensate.

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