So i had a customer walk in the shop with 2 broken exhaust manifolds from a boats inboard motor. They hadn't been flushed with antifreeze before winter and cracked open.
This one had a fully broken off chunk which made it an easier repair, grind the edges & weld.
The other one was still in one piece & the guy had tried to fix it with JB Weld... ffs people... stuffing epoxy in a cracked cast iron manifold.
So first I dug into it with a die grinder to bevel both edges. Then I had to find out exactly where the crack ended on both sides to drill a hole & stop the cracking, skip this step & the repair will be useless because it will reappear over time.
I used a penetrating dye system to expose the ends of the crack. First I sprayed the dye & let it seep in for 10 minutes.
So I switched my attention to the other manifold and started beveling the edges.
Then I sprayed the developer on the first manifold to make the dye come up out of the crack. After a few moments I could see where the crack was headed.
So I drilled the ends When i finished digging at it with the die grinder, I found that the crack had a split in it so I drilled a second hole.
I cleaned out the remaining epoxy with a wire brush & it was ready to pre-heat.
I clamped it down to close the gap as much as possible.then I wrapped it in fiberglass tarps & started heating it up to 200°C. Then I tacked it to remove the clamps.
Then it was time to start welding it. Welding cast iron is a lengthy process, with this rod the interpass temperature can't exceed 300°C or go below 250°C, the welds have to be peened to prevent cracking when it cools down. Peening means hammering the surface with a chipping hammer after every pass, which shouldn't exceed 3/4" in a single run, also to prevent cracking. Cast iron parts don't like rapid expansion followed by a rapid contraction.
Once it was done i put it in a bucket lined with vermiculite & filled it up then covered it to then let it cool down overnight.
Next I got to welding the 2nd manifold. Preheated it and then welded the easy part while flat on the table. Did the rest with the manifold standing up, then i wrapped it in tarps & moving blankets because i didn't have enough vermiculite left to fill a second bucket.
The next day I did a few touch ups on the first one, very short passes without preheating but loads of peening. Then i started grinding the bolt holes clear & then a quick surface grinding to remove the lumps from doing short overlapping passes.
Then a quick paint job before calling the customer & giving him the bill.
I used 8 rods at 10$ each (cast iron is expensive to weld) and added 10$ for abrasives & paint. So I spent a total of 6 hours on this job at 60$ an hour for a grand total of 450$.
I don't know what engine they came from but apparently they are hard to find so it was worth it to save these water cooled inboard motor exhaust manifolds. The customer was very happy to have a weekend project of putting it back together & trying it out on the water.