Welding steel tube inside cast aluminium

[paul_f]

I am doing a throttle body conversion, where the original manifold ends are steel tubes with cast aluminium on them (ally is about 5mm thick)

So that the throttle bodies line up correctly(the bore centres are about 10mm off) and I have smooth ports I need to build up the inside of the tubes so that when the ally flange is welded (will get that done with a TIG) there will be a smooth transition.

However I am concerned that if I try and weld a bead onto the steel tube the ally will melt? Am I correct in thinking this?

They look like this

Cheers
Paul

 

[Shox Dr]

There is a very high probability of the alloy melting. Alloy Castings tend to have a lower melting point, of other alloys because of the addition of other metals (Zinc etc) to aid casting.

That and Steel has a highter melting piont to ali, but you knew that

 

[paul_f]

Thanks for the reply. I guess my other option would be to grind away the steel tube and then have the ally casting build up with the tig welder?

 

[paul_f]

I was wondering whether I could possibly mig braze this? Would that be at a low enough temperature?

Cheers
Paul

 

[madkayaker]

might melt the ali

 

[hotrodder]

While the melting point of Al is considerably lower than for steel it's a much better conductor of heat- typically need more amps to weld aluminium than steel, at least until the part is heat soaked.

If the Al casting has a wall of around 5mm it's going to take some heat input to melt. With a bit of care (plenty of tea/beer/cider breaks etc) to keep the temperature sensible you should be okay. Personally i'd be more concerned about the different rates of expansion between the two metals but i suspect that as long as you don't let the thing get too hot you should be okay. However...

Might got have got the wrong end of the stick but from the pic posted wouldn't it be easier to correct the bore centres by cutting and shutting the flange?

 

[paul_f]

Thanks for your reply. I can't correct the bore centres that way as this is the manifold end piece that bolts to the head. I am having flanges welded to these to bolt the throttle bodies onto the engine.

Cheers
Paul

 

[hotrodder]

What i mean is a small pie cut to the flange (at the head end) to angle the manifold runners (exaggerated lots in pic) slightly around their existing bore centres



Might have the piecut round the wrong way (depends whether the bore centres need moving apart or closer together) but what i'm thinking is split the head flange and pivot the runners to correct the bore spacing at the other end. Depends on the length of the manifold as to whether it's going to workable or more trouble than it's worth regarding the corrections that'll be necessary to mounting holes. Might still have this very wrong as i've only seen part of the manifold though

I'm thinking it'll be a lot easier and faster to weld up, redrill a few mounting holes and linish the flange than to build up the ID of the runners and spend ages with a die grinder blending it all in