Welding a broken cast iron manifold

[Jonny69]

Somehow I managed to shear the end off my exhaust manifold where the pipe attaches on the way to the NSRA Supernats. Irritatingly I threw my spare one away thinking I'd never need it so I upgraded to a tuned tubular jobbie, only now I'm "untuning" the engine so it lives a bit longer and I want to go back to the stock inlet and exhaust. I could either look for another manifold for a pittance or try and fix my broken one. I like fixing things and I'm a tight fisted miser so lets get on with it...

These are the two bits that need sticking back together:





I've cleaned them up as best I could and ground a shamfer on the edges so the weld has somewhere to go:



Cast iron is brittle and welding a cold manifold will probably crack it so I'm going to preheat it and weld it hot. She's out in case anyone is wondering. I wouldn't normally get away with this:



Gas mark 7 for 30 minutes, that's 220 degrees in new money. 'Scuse the state of the oven, I know I really should clean it...



While the manifold was in the oven I had a quick practice laying down some short beads on some scrap thick steel. Welder up on full:



When it came to the real thing I was expecting to use full power but the iron on the manifold is very poor and was just blowing away. I knocked the power back a notch to get a few weak tacks in place then basically worked my way round using the tacks as a starting point to melt in a small pool to fuse the two parts together. There was no way a continuous weld was going to work so it's not pretty but it's fixed:



In hindsight I think next time I have to repair something like this I'll gas weld it because it'll give me more control over what melts where and it'll result in a much neater join with better penetration. The amount of muck in the iron wasn't helping at all and made a lot of mess with the MIG.

[LeperousDust]

Looks a damn sight better than i could ever do. You always surprise me with your bodgings Jonny, its a pleasure to read what you're upto as always

[Desmo]

Aye. I don't have a clue what most of it is, but find it strangely interesting

[Jonny69]

Heheheh

[Feek]

Originally Posted by Desmo

Aye. I don't have a clue what most of it is, but find it strangely interesting

As do I, it's fascinating

[Garp]

Originally Posted by Feek

As do I, it's fascinating

Me three.. I'd love to be able to weld, but then I don't have anything to actually use it on or any actual need to!

[Jonny69]

Neither did I until I got a welder

[phykell]

Don't be tempted to grind down the weld, even if it doesn't look the grinding has weakened the weld, it will have done.

The only problem you now have is that if you managed to shear the thing off in the first place, the weld is going to be under some stress. I don't know the engine but the chances are that either the downpipe, and perhaps the rest of the exhaust, could do with refitting - loosen everything off on the downpipe, etc. when you refit the manifold. Another possibility is the engine mountings. Replace the rubbers as a matter of course.

Nice job btw

[Jonny69]

Not sure what caused it to happen in the first place but my guess is because it's a stainless aftermarket exhaust from the owners' club there's less give in it and it's loading the manifold up or something. General thought is it isn't going to last long anyway because welding to cast doesn't work too well, it's just got to last long enough to find another manifold locally which will set me back all of a tenner I expect.

[phykell]

That sort of thing is due usually to flexing - cast iron is extremely strong so it's unlikely to break just because of extra weight but add the extra weight to some flexing...

As I say, check your engine mounts - is the engine transverse mounting or inline? If it's transverse, *definitely* check the mounts. I recall from my Mini (A series engine) days that there was a device which would bolt to the bulkhead to augment the inadequate (having tuned the engine at all) engine mounts. Perhaps there's something like that for yours or you could fabricate something. I also recall that you can buy hard (nylon) bushes for the engine mounts which, also they transmit noise, are far better at holding a tuned engine in place than the standard rubber bushes.