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Welding a crankshaft?
Canuck750:
Has anyone have experience welding up the end of a crankshaft? A Benelli single motor I recently picked up has a damaged threaded tip on the shaft end that secures a magneto. Looks like someone tried to get a very seized magneto off the taper and whatever puller was used damaged the shaft. About a 1/2 inch of the shaft is missing.
This crank is a spare but I would like to save it if I can
My thoughts are to use a 4 jaw independent Chuck and true it in the lathe, shave off the damage and using MIG weld it back up then turn the tip back to dimension and thread it in the lathe.
It’s not a load bearing part other than it holds the big nut that compresses the magneto onto the shaft.
Thoughts?
To get this magneto off I ended up grinding the brass magneto body off the steel center section so as to get oxy/acet onto the magneto sleeve, red hot, then a big bearing puller. A typical rotor extractor did nothing but damage the crank tip even more.
nc43bsa:
With that much damage, I think you would be better off finding find someone who could make a new crank half.
<edit> Is the main shaft pressed into the crank cheek?
nc43bsa:
OR . . .
You could have the threaded portion cut off the main shaft, drill and tap the shaft, and fabricate a threaded piece to replace the damaged portion.
Triumph twins retained the alternator rotor with a threaded stud and nut for decades.
Canuck750:
--- Quote from: nc43bsa on December 04, 2022, 09:44:30 PM ---OR . . .
You could have the threaded portion cut off the main shaft, drill and tap the shaft, and fabricate a threaded piece to replace the damaged portion.
Triumph twins retained the alternator rotor with a threaded stud and nut for decades.
--- End quote ---
Now that’s an idea I hadn’t thought of, interesting.
The shaft and flywheel are one piece.
nc43bsa:
--- Quote from: Canuck750 on December 04, 2022, 10:02:04 PM ---Now that’s an idea I hadn’t thought of, interesting.
The shaft and flywheel are one piece.
--- End quote ---
If you go that route, I'd red loctite the new piece into the crank. If you ever need to remove it, you can heat it with a Mapp gas torch.
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