I've Mig and Tig welded cast iron. Sometimes it works, sometimes it doesn't. The good news is that it usually works on barrel fins and with fins it really doesn't have to be phenomenally strong...preheat also helps.
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Re: Broken cast iron barrel fin fix?
#424381 03/15/1210:17 pm03/15/1210:17 pm
I've seen fins attached with a mig welder thT looked pretty good (probably stainless wire,I only saw this in a video)preheat is the way to go , aas well as post heat .The trickk I have heard is to place the pieces in an old charcoal grill buried in the coals . By the time the coals are glowing the pieces should be evenly and slowly heated . attach the fin and place back in the coals for a more controllled slow cooldown.This is to prevent a rapid heating/cooling that tends to crack along the joint.I've never tried this .
It can be braze-welded with a little prep. Bevel the surfaces and apply a 'tinning' pass of brass rod with an oxy-acetelyne torchh with the flame set to 'carburizing'. Thin fins should respond well to a pre-heating from the torch. Then you can easily pass a smoth bead of pooled brass to quickly fill the gap. Pre-heating helps to prevent shrinkage problems with the joined surfaces.
I've used MIG on cast iron several times, engine blocks, carb flanges etc. Lay a little puddle(till it just wets out) and get out. Let it cool completely and hit it again. I believe that preheat on small pieces sets up stresses. Veed out and surgically clean is the key, as small a vee as you can possibly get away with. IMO nickel stick and braze imparts way to much heat.
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i would braze a reinforcing bracket perpendicular to the break tha bridges the gap to the next fin.just sort of a small shelf or stud to reinforce,but not stop heat from escaping.then braze the break and paint the braze black.
If it's not a show bike, why not just locate and (3/32") pilot-match drill the broken and 2nd fin approx. 3" or so apart, tap the 2nd fin for 2pcs #8 or #10 s/h flat-head screws (drill and countersink the broken one out to fit the screw) and just screw the top one down tight, using a few washers as spacers. Out of sight...out of mind.
I wonder how well that torch would work on frame tube? I've welded a cast iron water jacket on my 1937 John Deere with nickel rod but can't remember the alloy as it was in the late eighties. It can be done.
Last edited by revnosebone; 05/01/128:26 pm.
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for what its worth, cast iron cracks on cooling. to re-attach the fin bevel one end of the broken piece lightly then cold weld to the barrel. a couple of small tacks the lightly peen the tacks with a hammer to help against shrinkage,let cool till you can keep your hand on it then repeat the process as needed. done a lot of cast this way without problems.PATIENCE IS THE KEY.