The $5000 general purpose motorcycle

gungasnake (51)in #manufacturing • 5 days ago

The $5,000 American Motorcycle: An Exercise in Simplicity

I got to thinking recently about motorcycles and American manufacturing.

Suppose, for the sake of argument, that I were Elon Musk—or somebody with considerably less money but enough capital to start a serious manufacturing operation—and wanted to build a motorcycle that could be sold in large quantities for something around $5,000.

The objective would not be to build the world's fastest motorcycle.

It would be to build a reasonably fast, sporty, exceptionally durable motorcycle that was gigantically simple and functional.

I think the United States needs to be able to manufacture things like this again. And motorcycles may represent a much easier entry point into vehicle manufacturing than automobiles.

What Would the Motorcycle Look Like?

My starting specification would be something like this:

Approximately 600 cc
Inline three-cylinder engine
About 200 cc per cylinder
Short-stroke design
Two valves per cylinder
Pushrod valve operation rather than overhead cams
Hydraulic lifters—no periodic valve adjustment
Electronic fuel injection
Air/oil cooling
Spin-on automotive-type oil filter
Five-speed transmission
Modern toothed belt final drive
Cast aluminum wheels—no spokes
ABS disc brakes
Simple steel-tube frame
Approximately 55–65 horsepower
Approximately 350 pounds
Comfortable sustained operation at 75–85 mph
Price target around $5,000

The idea is not primitive technology. It is modern technology used selectively.

Put sophistication where sophistication accomplishes something useful. Eliminate it where it merely adds cost, maintenance and failure modes.

Why Three Cylinders?

I would be reluctant to abandon the three-cylinder engine simply to save development money by buying somebody else's existing parallel twin.

Three cylinders seem almost ideal for a 600 cc motorcycle.

A 600 cc twin has fairly large 300 cc cylinders. A four has four little 150 cc cylinders and all of the additional pistons, rods, valves, injectors and associated hardware.

A triple gives you three very manageable 200 cc cylinders.

A conventional four-stroke inline triple with a 120-degree crankshaft also has a distinctive smoothness and exhaust note. It provides much of the refinement of a four while retaining some of the mechanical simplicity of a twin.

There is also historical precedent for small three-cylinder engines.

As a teenager, I owned a DKW automobile built by Auto Union, the company lineage which eventually became today's Audi. DKW and other European manufacturers produced numerous small three-cylinder two-stroke engines.

My father thought the DKW was unsafe and made me get rid of it. Knowing what I know now, and with my present attitudes, I think I'd have kept it.

Our hypothetical motorcycle would obviously be a modern four-stroke rather than a smoky old two-stroke, but the underlying idea remains attractive: small displacement, low weight and intelligent engineering rather than brute force.

Short Stroke and Pushrods

The pushrod engine deserves some explanation because contemporary motorcycle buyers have been trained to regard overhead cams as inherently superior.

They aren't inherently superior for every purpose.

Overhead cams become particularly advantageous when an engine is expected to operate at extremely high RPM. A pushrod valve train contains more moving mass—the lifter, pushrod and rocker all have to accelerate and decelerate along with the valve.

But why does our motorcycle need to turn 14,000 RPM?

It doesn't.

A short-stroke engine substantially reduces mean piston speed at a given RPM. Something around a 72 mm bore and 49 mm stroke would produce almost exactly 600 cc in a three-cylinder engine.

At 8,000 RPM, mean piston speed would remain quite conservative.

Design the engine to make perhaps 55–60 horsepower at 7,000–8,000 RPM, rather than trying to extract 120 horsepower at astronomical engine speeds.

Then use modern lightweight pushrods, hydraulic roller lifters, good rockers and sensible valve springs.

The result should be an engine that provides all the power a road motorcycle actually needs while eliminating periodic valve-clearance adjustment.

How Much Horsepower Do We Actually Need?

My brother once owned a Honda CB750 K1.

That motorcycle could achieve speeds somewhere in the 120-plus-mph neighborhood with only about 67 advertised horsepower.

Once, simply to find out what it felt like, I opened that Honda up to roughly 130 mph for perhaps half a mile.

That was enough.

Despite having accumulated a very large amount of motorcycle mileage, mostly commuting in and around the Washington, D.C. region, I don't recall ordinarily doing much more than about 80 mph.

That raises an obvious question.

What practical purpose is served by a street motorcycle producing 150 or 200 horsepower?

There are people who genuinely use extraordinary motorcycle performance on racetracks. Fine.

But I suspect an enormous number of modern motorcycles are purchased partly for a macho image and for performance capabilities their owners will never actually use.

Our $5,000 motorcycle doesn't need to win a specification-sheet contest.

It needs enough power to accelerate hard, merge into freeway traffic, pass a truck quickly and cruise all afternoon at 80 mph without caring.

In a 350-pound motorcycle, 55–60 horsepower should accomplish that very nicely.

Design It for 80 MPH, Not 180 MPH

I would make 80-mph durability a much more important engineering specification than maximum speed.

Can the motorcycle run 80 mph for three hours through Texas in August?

Can it sit in stop-and-go Houston traffic without overheating?

Can somebody commute on it five days a week for ten years?

Those questions matter more to me than whether a magazine test rider can make it go 147 mph.

The engine should be deliberately understressed.

Instead of designing a 600 cc engine to produce 120 horsepower and hoping it survives, design one to produce 60 horsepower and try to make it last 150,000 miles without being opened up.

Air/Oil Cooling

Pure air cooling would be attractive because it eliminates the radiator, water pump, coolant, thermostat and hoses.

The difficulty with an inline triple is cooling the center cylinder.

The solution might be air/oil cooling.

Use generous cylinder and head fins, piston-cooling oil jets, a small oil cooler and perhaps a thermostatically controlled electric cooling fan for prolonged operation in traffic.

That retains most of the mechanical simplicity of an air-cooled engine while giving additional thermal control when it is actually needed.

Use an Automotive Oil Filter

I would deliberately design the lubrication system around one of the world's most common spin-on automotive oil filters.

Pick a thread and gasket configuration used on millions of small cars and industrial engines.

Then the owner can buy a Fram, Wix, Purolator, Bosch or whatever equivalent brand is available locally.

This principle should extend throughout the motorcycle.

Wherever possible use:

Standard industrial bearings
Standard metric fasteners
Common automotive relays
Ordinary blade fuses
Common spark-plug dimensions
Standardized fuel injectors
Standard electrical connectors
Easily available batteries

The parts catalog should contain as few strange proprietary parts as possible.

A motorcycle sold throughout the world shouldn't become unusable because somebody can't obtain a $37 proprietary relay.

Belt Drive Instead of Chain

I would definitely use a modern toothed belt for the final drive.

Modern synchronous belts using extremely strong tensile cords can handle far more power and torque than our relatively modest 600 cc engine would produce.

The belt should deliberately be overengineered.

If calculations indicate that a 25 mm belt is sufficient, perhaps use 30 or 32 mm. Use reasonably large pulleys so that the belt isn't continually bending around unnecessarily small radii. Protect it against stones and road debris.

Then put the manufacturer's money behind it.

I'd like to see something like:

FINAL DRIVE WARRANTY: 6 YEARS / 60,000 MILES

The normal maintenance schedule could almost be amusing:

Every 5,000 miles: Inspect drive belt.
Lubrication: Never.
Adjustment: Only when required.

No chain oil.

No chain cleaning.

No lubricant thrown onto the rear wheel.

No routine chain-and-sprocket replacement.

If endurance testing demonstrated that the belts routinely survived 100,000 miles, perhaps specify preventive replacement somewhere around 75,000–100,000 miles.

Keep the Transmission Simple

Does this motorcycle really need six gears?

Probably not.

With a reasonably torquey 600 cc triple, I'd seriously consider a five-speed constant-mesh transmission, conventional wet multiplate clutch and a fairly tall fifth gear for highway cruising.

I'd probably use a cable-operated clutch rather than hydraulic operation.

Again, the question for every component should be:

What is the simplest thing that performs the required function reliably?

Forget the Carbon-Fiber Frame

My original thought was a very lightweight carbon-fiber frame made from standardized tubes bonded together.

That is technically possible, but it probably violates the economic philosophy of the project.

Carbon fiber introduces material expense, manufacturing-process controls, inspection problems and difficult crash-damage assessment.

A simple high-strength welded steel-tube frame makes more sense.

Perhaps it weighs eight or ten pounds more.

Who cares?

Anybody from Texas to Thailand can understand it, inspect it and weld it.

Use the engine as a stressed or semi-stressed structural member and there shouldn't need to be very much frame in the first place.

Don't Build Six Motorcycles

Build one motorcycle platform.

Then bolt different things onto it.

A small windshield and bags produce a touring version.

Different bars and seat produce a standard.

A small fairing produces a sport version.

Longer suspension and different tires produce a scrambler.

Keep the engine, transmission, ECU, electrical system, brakes, wheels and most of the chassis identical.

And make a promise that seems almost revolutionary today:

We intend to manufacture this basic engine and drivetrain for twenty years.

That means suppliers can justify tooling.

Independent mechanics learn one engine.

Parts remain available.

Owners don't discover that their seven-year-old motorcycle has become an orphan.

The Japanese Example

There is some historical precedent for this entire philosophy.

Postwar Japanese motorcycles became an extraordinary training ground for manufacturing expertise.

Honda in particular spent the 1950s learning how to manufacture small, light, reliable, sophisticated engines cheaply and in enormous quantities before becoming a major automobile manufacturer.

Suzuki similarly moved from weaving machinery into motorized bicycles and motorcycles before becoming an automobile producer.

Toyota and Nissan had different histories, so it would be wrong to claim that the entire Japanese automobile industry originated with motorcycles.

But motorcycles provided an important industrial school.

A motorcycle requires an engine, clutch, transmission, brakes, suspension, electrical system, bearings, controls and precision manufacturing—many of the same disciplines required for automobiles—but requires vastly less material and capital.

That raises another possibility.

Rebuilding American Manufacturing from the Motorcycle Up

I believe the United States needs to retain—or rebuild—the ability to manufacture motorcycles.

I don't see the existing American motorcycle industry necessarily supplying the inexpensive, practical, mass-market machine I'm describing.

But perhaps that creates an opportunity.

Starting a motorcycle manufacturer should be vastly less expensive than starting another Ford, Toyota or Tesla.

And the company wouldn't initially need to manufacture everything.

Purchase excellent brakes from a specialist.

Purchase ABS components.

Purchase injectors.

Purchase tires, bearings, electrical components, suspension components and sensors.

Concentrate the company's engineering resources on the engine, drivetrain, chassis and integration of the complete machine.

The initial factory could largely be an engine-assembly and motorcycle-assembly operation, with specialized components produced by suppliers.

And Now There Is AI

This equation may have changed considerably in the last few years.

Traditionally, a clean-sheet engine and motorcycle required substantial engineering organizations.

Engine designers, transmission engineers, draftsmen, CAD operators, analysts, documentation people, manufacturing engineers and many others spent years generating calculations, drawings, tolerance analyses, revisions and reports.

Modern CAD/CAM/CAE had already reduced that labor dramatically.

AI could reduce it further.

A very small engineering organization can now explore bore-and-stroke combinations, compression ratios, piston speeds, valve areas, injector sizes, bearing loads, cooling requirements, gear ratios and hundreds of other design decisions extraordinarily rapidly.

Change the stroke from 49 to 52 mm?

The consequences throughout the design can be recalculated almost immediately.

Change the rear tire diameter?

Recalculate all five transmission ratios and final-drive gearing.

Move an engine mounting point?

Check what else it affects.

AI doesn't eliminate competent engineers.

It can make one very good engineer enormously more productive.

A project that once required a large engineering department might someday be practical with perhaps a dozen or two exceptionally capable engineers using modern CAD/CAE systems, AI assistance, contract prototype manufacturing and established component suppliers.

But You Still Have to Break Engines

There is one place where computers and AI cannot substitute for reality.

Eventually you have to make metal.

Build prototype engines.

Put them on dynamometers.

Run them at full power for hundreds of hours.

Tear them apart.

Find out what wore.

Discover that the center exhaust valve runs hotter than expected.

Change it.

Build another one.

Then put engines into motorcycles.

Run them through Texas summers and northern winters.

Run them in rain.

Run them in traffic.

Give them bad gasoline.

Let test riders abuse them.

If the selling proposition is simple and nearly indestructible, I'd rather spend millions trying to destroy fifty prototype engines than spend those millions adding electronic gadgets.

The Real Innovation Is What You Leave Out

Eventually the specification might look something like this:

600 cc inline triple
Approximately 60 horsepower
Short-stroke OHV engine
Two valves per cylinder
Hydraulic lifters
Electronic fuel injection
Air/oil cooling
Automotive-type spin-on oil filter
Five-speed transmission
Carbon-cord toothed belt drive
Cast aluminum wheels
ABS disc brakes
Steel-tube frame
Approximately 350 pounds
$5,000 target price

No electronic suspension.

No six-axis inertial platform.

No four riding modes.

No electronically adjustable windshield.

No elaborate entertainment system.

No 180-horsepower engine.

No $12,000 price tag.

Make the brakes excellent.

Make the tires excellent.

Make the lights excellent.

Make the engine almost impossible to kill.

Make maintenance ridiculously easy.