Well, the title says it all, can a broken and missing fin be repaired? I always thought cast iron couldn't be welded but then again I thought marriage was a good idea too.

Hi Samuel.
Cast iron can be welded with an arc welder with electrodes that have a nickel iron core.

http://www.ebay.com.au/itm/Welding-Rods-2-5mm-3-2mm-Cast-Iron-Stick-Electrodes-/140498181464?pt=AU_Welding&hash=item20b6581d58&_uhb=1#ht_2156wt_1163

A good measure is to wrap them in a blanket after welding, to cool down slowly, say over night.

Did this to a few fins on my cylinder nearly 25 years ago and haven't lost one yet.

email (option): spacemonkeym@gmail.com

I've had lots repaired over the years. I leave it to the professionals. One bloke brazes new fins on and others have used TIG welders. One bloke even built up a fin with TIG that was impossible to get at for a normal repair. Dave Plumb is good at all this stuff and not expensive........It's the postage that can be the killer! Ron

email (option): ronpier@talk21.com

Samuel, do you have a mig welder with normal steel wire? If you do, grind the metal clean on the broken fin and place a small blob of weld on it and leave for a minute or so, then do the same again and so on until you've built it back up. It will probably take all day as when you weld it, it should never get hot at all it's very time consuming, but main thing is that the cylinder should never get hot or even warm in the slightest, if it does you are doing it too fast and it will crack when it cools. Basically you should be able to touch the blob of weld with an ungloved hand after a few seconds of welding it. I've done a few like this and it does work well, just remember it isn't a race and I'd plan for it take nearly all day. the idea of welding it like this is to allow the iron's particles to re-arrange themselves slowly, if you do it too fast the particles pull against themselves and will cause a crack, as you know iron is no good under tension! Try to build the weld to overhang the original fin so that when you dress it back up are able to grind it flat without there being pits from the seperate blobs of weld.
If it is a top fin, don't try to weld a piece in there as it seems that any fin that has a curve in it (or has broken to an angle of more than 180 degrees) will definately crack if you try to weld a piece in there) If the break is less than 180 degrees it may weld ok with donor broken fin from another barrel, but the problem then is that you can never get to the underside of the fin and you can still tell that it has been broken.

email (option): davmax@ntlworld.com

The guy that does my welding will weld on top or bottom fins that are broken..I buy damaged barrels at the jumbles so that I always have a source of fin 'pieces' which I shape up and then he welds them...This generally works fine, though the comments about slowing down the cooling are relevant here...For fins that are broken part way down a barrel or head it is impossible to get at them to weld a piece on. In that case I shape up a piece which is then tack welded in place at the ends and then brazed. The braze flows along the joint and makes a good repair. This can also be done after an exposed fin is welded on to give the 'back' of the weld, which can't be accessed, a good appearance..I haven't done it but I imagine a silver soldered repair could be successful as well as it is quite a strong material....Ian

email (option): ian@wright52.plus.com

Thanks guys, Dave, I wish I could have you do it for me but I think it would be cheaper to fly you over here than ship the cylinder to you. I guess the trick is to find someone who I can trust enough to do it as you say without rushing it. Unfortunately, soldering copper pipe is the extent of my ability so I'll have to leave it to someone else. Doner cylinders are non existant, so the whole thing will have to be built up. You use just regular steel wire??

Hi Samuel...Head for your local scrap yard if you have one...I bet you will find some 'donor' material there. You can use cylinder fins but I have also used the cast iron vanes from compressors and pieces of mild steel shaped to the correct tapered profile by hand...Ian

email (option): ian@wright52.plus.com

I just use mild steel with brazing.

Never thought of that Ian, my father -in- Law's compressor might be missing a fin next weekend!!

Yes, you can just use steel wire if you use the method above, if you weld a piece of broken fin on you would have to use a dissimilar metal such as nickel or stainless

email (option): davmax@ntlworld.com