“It” could be anything. Once upon a time the phone rang here and it was two fellows with no mechanical experience, asking if I would be willing to answer their questions by phone as they undertook to change the crank in their RD350 Yamaha. Since I’m a strong believer in diving in and learning skills, I said yes.

The process took two weeks and it was rewarding. A lot of the fear in such work is unfamiliarity, so I tried to map out in words what they were about to encounter at each stage. They did the job and we were all pleased.

My maternal uncle had showed me how we could disassemble the lawnmower engine, fit new rings to its piston, break the glaze on the cylinder wall, and re-seat the intake and exhaust valves using Permatex valve-grinding compound. We removed and replaced old gaskets, cleaned up all parts, pre-oiled moving parts, and reassembled. The engine ran normally.

My dad at various time would ask me, “What makes you think that after all this scrambling of parts and all the complexity, this thing can ever run again?”

I thought for just a moment, then said, “If it has air, fuel, compression, and timed spark it has to run.”

There was a time in this country when millions of men and women worked in factories and were therefore acquainted with the fundamentals of machinery and, in general, physical reality. There were also plenty of those masters of improvisation, farmers. That in turn assured that when a Sergeant called out to the assembled company, “All RIGHT – which one of you sad-ass bastards can weld? (repair radios, time a magneto, &) two or three hands would go up and the job would get done.



My middle son’s experience in Helmand Province, Afghanistan, was that one could get in big trouble for attempting to repair or adjust equipment. Only an accredited rep of the manufacturer was authorized. Is that because everything’s now such high-tech? The device in question was a big, crude mine roller. There were six on the paperwork, none usable. And in vehicle “dead parks” there were acres of outright blown-up or merely damaged vehicles. It was forbidden to take usable parts from any of these hulks to repair active equipment. As he finished the repair, an officer walked up, ready to write him. Fortunately the officer who needed a working roller (yes, you can “detect and detonate” mines by walking or driving vehicles over them, but there are better ways) was of higher rank. He expressed delight at now having one working mine roller.

I began learning to rebuild pressed-together two-stroke crankshafts by saying “Yes” to someone with a rattled-out OSSA crank in one hand, who asked me, “Do you know how to rebuild these things?”




How hard could it be? It was a single-cylinder crank, consisting of two flywheels, each forged in one piece with its mainshaft, joined together by a pressed-in-place crankpin. Slid onto the pin would be the one-piece connecting-rod (not split-and-bolted) with a caged needle roller assembly that ran against the pin and the hardened ID of the rod big-end, with a brass side-washer on either side.

Once it was pressed together with a new rod, pin, bearing and washers, it had to be “trued” – aligned by a process of checking its alignment with a dial gage, then using a soft copper hammer and some judgment to tap (yes, it’s a euphemism) in the right place and with the right vigor to “jar” the parts toward alignment. This took an afternoon in a student machine shop.

Frustration is possible. For example, a frequent result was tapping harder and harder to correct a .004” error, only to find that, after hitting hard enough to create movement, the crank was now .004” out in the opposite direction. So you try different things, all the while accumulating little useful bits of experience. Improvisation. Discarding ideas that failed, keeping those that worked.

I rebuilt a lot of cranks after that – at first for street stuff at the Yamaha dealer, and later many more for Yamaha’s TD and TZ production road race engines.

Thousands of others learned this work in dealerships or machine shops all over the place, showing that anyone with reasonable sense and persistence can learn it.

This is why I confidently suggest to people, “Become your own expert. Dive in and teach yourself.”

When a late-model 600 engine was needed for a video, someone went to the junk yard and bought an engine out of an insurance write-off for $150. We took it all apart on camera and showed how the innards looked and functioned, and then someone on the video crew offered $150 for the parts – for his own education.

Learn new stuff, get your hands on the real thing, and have fun at the same time.