Unbendable casting!

[AJWParticipant @ajw]

[AJWParticipant @ajw]

Cracking on with my Centaur build I have now got to the cast gunmetal head casting.
I noticed one of the rocker lugs was out of line and would not be recovered in machining.
So I had a bright idea of heating the affected area with my propane/oxygen torch so I could ‘bend it straight’
It just cracked and broke off! Well happy.
I take it cast gunmetal is quite hard and in annealable?
You live and learn.

Alan

[Michael GilliganParticipant @michaelgilligan61133]

Condolences, Alan

My guess is that you de-zincified it by using the torch.

MichaelG.

.

https://en.m.wikipedia.org/wiki/Gunmetal

http://www.airproducts.com/Industries/Metals/ask-the-experts-metals/heat-treating/dezincificatiion-apply-thermal-processing-brass.aspx

Edited By Michael Gilligan on 30/11/2018 21:56:07

Edited By Michael Gilligan on 30/11/2018 21:59:16

[JasonBModerator @jasonb]

I find GM castings are very soft and easily bent if you are careless with your clamping or have a major tool dig in. Probably would have been better to tweak it cold. Only last week I had some GM bearing s that had cupped a bit and just gave then a good squeeze in teh vice to flatten them out before starting to machine, these were 1" x 1/2" section.

On the bright side it is easier to silver solder the offending part back on than it would be with an iron casting.

[MichaelRParticipant @michaelr]

Sorry to hear that, I had the same problem on my Centaur cylinder head I got it back inline by bending cold, as Jason says you should be able to silver solder the arm back on.

[AJWParticipant @ajw]

In hindsight I should have checked it over better upon receipt when I would have spotted it and had a word with the supplier or sent it back!
I get the feeling that the bend was caused as it came out of the mould, dropped?
I’m not sure about silver soldering it back, there is a crack further down the arm meaning I would have to remove it first, meaning 2 breaks in the same section. On top of this the arm, which is webbed, still has a bend in it!

Alan

[Former MemberParticipant @formermember19781]

[This posting has been removed]

[Nigel BennettParticipant @nigelbennett69913]

Many copper alloys are known as "hot short". This means that they don't take kindly to being battered when hot. I found this out myself once when trying to form a head on a piece of bronze bar. It simply turned to mush under my hammer! Hence forming copper alloys is generally best when they're cold.

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