Not for the weak minded.

John Deere 3hp, Episode 5: Epic Welding

December 5th, 2007 Josh

As I got to the point where I decided to start reassembling the engine, I discovered the worst broken part of the entire build. The left side flywheel was bent and 3 of the spokes were cracked all the way through.


This repair took about 6 months to complete, and involved about 9 different attempts to weld the spokes back together. The reason it took so long is simply the time involved in welding the cast iron. The best way to weld cast iron is to heat the piece to within a few hundred degrees of the melting point of the braze, then braze the piece with any method that is most comfortable (Stick, MIG, torch), then put the piece back in the heat and slowly cool it back down. Unfortunately, I had no way to do that with the size of the flywheels. So I had to resort to the slow method: quick weld, followed by lots of peening, and waiting for the piece to cool back down to touchable temperature. This process took about 3-4 separate visits to the shop (at 1-2 visits/week) for just one complete weld on the 3 spokes. The process also proved very touchy. Letting the piece get too hot, welding too cold, not peening enough, or getting too much flux inclusion can all lead to a crack in the finished product.


After about 6 months of attempting to weld the spokes, I successfully welded 2 of them, and then finally the last one. I used bondo-glass to fill in the aesthetic details. I used a rotary file to contour the bondo’d areas and cut or sanded the flat areas. The holes had to be drilled out as well, and for that job I started with a small hand drill for the first pilot holes, then moved up to a 1/2″ chuck drill, but the chuck wouldn’t keep a good grip on the bit, so I had to break out Thor.

IMG_p980.JPGThor is a beast of a 1/2″ drill, it has an on/off trigger, full cast aluminum case, handle, and trigger. This drill is made by a company called Industrial Pneumatics Inc, is about 60+ years old and is the toughest drill I have ever used. It powered through the tough welding that intruded into the holes without breaking a sweat.

After the holes were drilled out I put a few coats of paint on and it was finished. It’s pretty amazing how long it took to do, but how short it took to write about. Check out galleries one, two, and three for all the flywheel repair pictures.