Cycle World Readers Are Knowledgeable, Smart, Imaginative

[Hugh Janus]

Kevin Cameron has been writing about motorcycles for nearly 50 years, first for <em>Cycle magazine</em> and, since 1992, for <em>Cycle World</em>. (Robert Martin/)

One of the great pleasures of walking around bike-racing paddocks is the opportunity to meet and talk with a surprising number of engineers and scientists. Many of their careers began with curiosity about that available, invitingly complex, and in-human-scale technology we know so well—the motorcycle. The same applies to many of Cycle World’s readers, whose comments appear on the CW website. A few who stand out: the inventor of the Gunn diode (microwave source on a chip); a neurosurgeon; a man who worked on the creation of NASA’s large vacuum rocket engine test chamber at Tullahoma, Tennessee; another who designed large magnet assemblies for high energy physics; a retired Israeli automatic weapons designer; and a Corvette suspension engineer. All had much to say.

Are Two-Strokes Emissions Disasters?

This variety and the number of comments on my recent piece concerning two-strokes suggest that reader ctromley’s efforts to save our souls—urging us to “let it go” because the simple two-strokes of the 1970s were emissions disasters—fail to consider that world trade is propelled by huge two-stroke marine diesel engines delivering a remarkable efficiency of just above 50 percent. Even if that weren’t so, many people remain fascinated by two-strokes, to the degree that several direct fuel injection and transfer injection two-strokes not only exist but meet present-day emissions standards.

Yes, those simple 1970s two-strokes did waste 30 percent of their fuel, a steep price to pay for their simplicity. Yet aren’t four-strokes also wasteful in their own right? Instead of efficiently delivering their charge air by means of a small rotary blower, as two-stroke marine diesels do, the four-strokes require their massively strong power pistons to waste half their time acting as low-pressure gas exchange pumps during their intake and exhaust strokes. This “half-timing” is what made early 1970s four-stroke GP bikes (mainly MVs) so vulnerable: once two-stroke breathing reached a serious level, a four-stroke had to rev twice as high to make equal power. Honda put huge effort and millions of dollars into its oval-piston NR500, aiming for 23,000 rpm. Despite a series of redesigns innovations like slipper clutches to soften engine-braking, the NR never won a single GP point.

Scholarly reader Basil traces the opposed-piston two-stroke diesel from the German Junkers aircraft onward through time to tank engines of the present era, complete with references. Perhaps he will throw light on this one: In World War II it was the “backward” Russians who gave their T-34 tank a V-12 diesel engine, while Germany, the mother country of compression ignition, continued to fuel their armor with gasoline, despite the greater risk of fire. Why?

The Issue of Two-Stroke Run-on

Another reader, ccRoselle, speaks of two-stroke engines operating despite “random spark.” I wonder if this refers to the ability of two-strokes to “run on,” even with their ignition switched off and plug leads pulled. This used to happen frequently in our dealership—coming from the shop we’d hear an engine’s sound rise as it revved off its tach—the mechanics knew the only thing they could do was close the tank petcock and wait. Because two-strokes all naturally retain some exhaust gas cycle-to-cycle, this run-on is just an accidental version of what is now hailed as “HCCI” or homogeneous charge compression ignition. The retained exhaust gas adds heat and active chemical species to the fresh charge, and the extra heating that occurs in compression leads to auto-ignition. Read about Mazda’s Skyactiv HCCI developments.

Those who were driving cars during the stutter-and-stall era of emissions controls (around 1977, when carburetors were enveloped in Medusa-like masses of black hoses) will remember that great big V-8s, when being switched off, would sometimes continue to run spasmodically (often backward!) before finally heaving a great shudder and stopping. It was the same basic cause: Intake air leakage, hot exhaust gas, and active chemical fragments retained from cycle-to-cycle, all acting as an ignition source as the piston neared TDC on its compression stroke.

Another scholarly observation comes from motojournalist Michael Esdaile, writing about the origins of the tuned exhaust pipe (aka expansion chamber) that enabled simple crankcase-scavenged two-strokes to dominate all GP roadrace classes by 1975.

Rolf Eriksson reminds us that if a fuel lacks natural volatility, preheating it can help. Some snowmobile carburetors were cored for engine coolant to assist in fuel vaporization in severe cold. And during Formula One’s 1980s turbo era of anti-knock toluene-based fuel, Honda preheated that fuel in a heat exchanger on its way to the injectors.

In a related comment, kjell describes Yamaha’s dual-fuel commercial outboard motors. One of two tanks contained volatile gasoline, the other much less volatile but cheaper kerosene. Operators would start the cold engine and warm it up on gasoline, then switch to kero once it was hot enough to vaporize that heavier fuel. American farmers in the Great Depression of 1929 resorted to the same concept, but improvised. Italians generally recognize that the best engineers come from farm country: Farmers, having no money, have always had to think up ways to make do, substituting understanding for new parts.

Gary Mathers, the former head of American Honda racing, once offered up this parable: The hay is tall, dark clouds are coming, and the baler is broken. Who can fix it? Do you call an engineer? No, because engineers study the problem for six months and then write a report. You call a farmer, because a farmer has to have that hay in the barn before the rain spoils it.

Brien Smith described his idea of two sandwiched rotary disc intake valves, by which intake duration could be varied with rpm. There is at least one “down-under” engineer of the Let’s-Do-It-Today! variety who has built and tested exactly that.

I am delighted that Cycle World has such a group of knowledgeable, imaginative readers. It’s like walking through the paddock again.

Source

[Buckster]

What you say @Tym?

[XTreme]

No mention of Julian or Eddie?

[Tym]

What would Hacksaw do?

[XTreme]

2 hours ago, Tym said:

What would Hacksaw do?

Or that loony Steve with the 919?

[Tym]

50 minutes ago, XTreme said:

Or that loony Steve with the 919?

That episode in internet history was freaking funny. You couldnt make that chit up. 

[XTreme]

54 minutes ago, Tym said:

That episode in internet history was freaking funny. You couldnt make that chit up. 

All the crazy twats in the world thrown into one place!

Then I turned up and brought another bunch with me.