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Bajaj breakdown part 2
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You may recall the story of my Bajaj Breakdown. Basically I just lost power and coasted to the side of the road. It was still running, just not producing power with revs. Good fuel, spark and air, just no power and a horrible noise with throttle.
The answer was simpler than what I feared. I thought that the crank bearing was failing, but I could not find any problem with the easily accessible things: the oil and filter were clean of metal, the valves were good and on spec, and the engine would start. I pulled the flywheel and it was apparent that I had experienced a common problem with these wonderful single cylinder motors - both Vespa 2-stroke and Bajaj and other 4-strokes that all use a "Woodruff Key". A Woodruff Key is a tiny half-moon-shaped piece of metal that is supposed to be softer than both the flywheel and the crankshaft of these motors. It is designed to break away in order to help minimize the damage to the rest of the engine internals, and would basically serve to kill the ignition of the motor when some event causes the relationship of the piston and the flywheel It's a complex relationship! And it's exactly what must have happened to the Bajaj. Perhaps I ran lean for a minute or two and the piston experienced more friction in the cylinder, causing heating and slowing the piston. Maybe it was the nut holding the flywheel on, backing off slightly, perhaps it was both. Whatever it was, the key melted and I lost proper engine timing. So it was time for a fix! The bad news is that my stock Bajaj Woodruff key not only broke/melted away, it also heated up the crankshaft enough to remove some metal from the key holder "slot". The right way to fix this problem is to replace the crank. An engine-out replacement of the crank will take hours or weeks for me to do, and the parts are expensive. That coupled with impending winter means that a engine rebuild is not likely. Welding metal into the ruined slot is the next recommended repair. I might get around to that as a next step, but I really wanted to get the scoot back on the road before winter.
As I was pondering these fixes, I remembered that the Woodruff Key is specifically designed to only locate the flywheel on the shaft, i.e. it doesn't "hold" anything on, that the nut's job. Enter a high-tech epoxy called "Quick Steel". I've used Quick Steel around the house and garage for years, and it's a true miracle in a tube. It's easy to use, very strong and workable so that I could essentially use it to place the key in the slot and file it away to make a perfect fit.
What's next: The conclusion of the Bajaj breakdown
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