welding question

[HoSS]

Where's the welding stig?

I have an exhaust manifold on an astra with a nice crack around it.

These things are cast iron right? Can it be MIG welded with steel wire?

Thanks, Hoss

[Troddenmasses]

It's do-able, but isn't pretty or very strong

Welding link

It would probably be better to bite the bullet and buy a new one.

[Mark]

I believe it can be welded, but usually usung a stick welder, and the correct cast iron welding rods. Not sure how successful MiG welding would be.

[T1G UP]

Cast needs pre heating to weld it,grind the crack right out them fill with mma cast rods.

In other words get a new one!

[Tonk]

wouldn't bother with mig,

u can braze a repair though, groove your crack out first though

[HoSS]

I have brazing kit too, could do that.

Do we think that's going to last, or should i find a unit from a scrappy? (the cost new is horrendous).

Cheers

[Tonk]

i brazed a repair to an exhaust manifold, was still fine when i sold it 7 years later

if u've got the kit then theres nothing to lose.......

[Kim Horsevad]

Where's the welding stig?

I have an exhaust manifold on an astra with a nice crack around it.

These things are cast iron right? Can it be MIG welded with steel wire?

Thanks, Hoss

It can be welded using ordinary MIG/MAG

First you identify and mark the ends of each crack. Inspect with at magnifying glass - some of the cracks are probably only hairline.

Then you drill through the material in each of the spots you have marked. This is to stop the crack from going further.

Then you heat the workpiece up. It should glow red. Use oxy-acetylene, oxy-propane or even an propane blowtorch (slow...)

When heated to red hot the welding can begin. Turn the power up - you need lots of energy as the melting point for cast iron is considerably higher than mild steel.

Do the weld as continous beads, but move the tip in small circles as you move down the weld. As the weld cools the welded area contracs. Plan your welding such as to induce minimum stress on the other components of the workpiece.

As the weld cools, tap very lightly with a hammer on the welding area, in an effort to minimise stress buildup.

You can get special electrodes for cast iron welding. They are preferred to mig/mag welding, but they do not produce miracles. For cast iron welding you really need to be able to heat the iron up to glowing red.

[HoSS]

Actually i'm not entirly sure if the manifold is cast iron.

The top part looks cast (similar to a LR part) but it is welded to a cylindrical expansion chamber which looks more like sheet steel fab, before passing to the exhaust joint.

Is it possible the whole thing is steel? Any easy way to tell?

[bishbosh]

Grinder

Steel = lots of red sparks

Cast Iron = no sparks / very few.

[roguevogue]

Grinder

Steel = lots of red sparks

Cast Iron = no sparks / very few.

Close, steel will give lots of bright orange sparks.

Hardened steel will give brighter almost white sparks which split before they go out.

Cast iron will give dark red sparks, it is quite distinctive.(Particularly low grades of cast will barely spark at all.)

[kiall]

Actually i'm not entirly sure if the manifold is cast iron.

The top part looks cast (similar to a LR part) but it is welded to a cylindrical expansion chamber which looks more like sheet steel fab, before passing to the exhaust joint.

Is it possible the whole thing is steel? Any easy way to tell?

it should be cast around piston 1 is it cracked ? if so the stud will problarly sheer taking it out i hade to do the same on my cavy as mentioned i also drilled a hole at the end of each crack

[Ally V8]

I Tig welded a couple of Vauxhall OHC manifolds a few years back,using a stick welding rod for cast iron with all the flux taken off.They weld beautifully with a bit of pre and post heat.