Is it possible to mig weld a gearbox mounting lug back on?

You don't say if it's steel or alloy?

Steel will be fine, as long as you've got quite a powerful MIG

An Engine block won't be Steel.

It will be Cast Iron which is very different.

You may make it stick together with a MIG welder but it will not be strong.

The problem happens because Iron castings have minute pockets of Graphite in the metal matrix and these bits of Graphite will contaminate the weld and it will not be very strong.

Cast Iron can be welded but you need an expert or specialist.

Have a read of this page; Lincoln Electric

I believe that cast iron can be bronze-brazed, but I don't know about its strength. Mind you, Caterham chassis used to be (may still be) bronze brazed.

its a zetec silvertop engine block, so cast iron. its been running with the lug broken off (but still in place as a snug fit) for some time. As im taking the engine out tomorrow was looking to try weld it back on if possible

http://www.mig-welding.co.uk/cast-iron.htm

Have a read

Can stick weld back on with cast iron rods, but you will need to get a grinder in because it wont be neat

I had the clutch cable lug snap on my type 9 and welded it back on by heating both parts up with the blow torch and using the mig. I then gently heated them less and less until they were lukewarm.

No sure if that is a proven method but it lasted a few years until the gearbox broke internally!

get some cast rods and stickweld it on then tidy up afterwards with grinder

I had a pair of steering arms on a car that had been lifted and someone had cut the ends of forming a fork rather than an eye which MOT tester pointed out wasn’t the safest way of arranging things
A local blacksmith fixed them using the pre heating technique, excellent result and not expensive
Good luck

What gearbox is it. If you can get it to me i will do it for you.

quote:

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Originally posted by madteg
What gearbox is it. If you can get it to me i will do it for you.

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I have had good success with welding cast iron exhaust manifolds with stainless MIG wire, but the only way it ever works for me is to get the casting as hot as possible prior to welding and let it cool very slowly. If you don't you can hear the cracks forming in the iron as it cools and the resulting join is very weak.

Then again that's fairly easy to do with an exhaust manifold, but quite a problem for an engine block.