If I were allowed to keeponly one of what’s nowhundreds of technical

manuals, books, and publica-tions that sit grease-stainedand tattered in my homelibrary, I’d put a death-grip onJ.B. Nicholson’s ModernMotorcycle Mechanics.While still the product ofhuman hands and consequent-ly imperfect as all earthlyproducts must be, no one onthe planet has ever done a bet-ter job covering mechanicalrepair in such a broad scopeof what’s now consideredclassic motorcycles. Lastupdated in 1974, MMM as Iwill henceforth refer to it hasbeen called “the motorcy-clist’s bible” for good reason.From BSA to Yamaha,Nicholson has something foreveryone.

Unlike many technical pub-lications that simply organize,illustrate, and regurgitatemechanical knowledge,MMM is the product of exten-sive hands on experience,refined over decades.Nicholson began selling and servic-

ing motorcycles in Saskatoon,Canada in 1933. Over this time he

An Oldie but a GoodieAn Oldie but a Goodie

Don’t pitch your Lucas rotor if the insert is a little loose

because you might be able to fix it. If the rotor is demag-

netized, however, it’s time for a new one.

Punch-locking involves the use of a punch as shown.

Work around the outside border of the insert, almost but

not quite touching the insert. The indentations made by

the punch often secure the insert.

J.B. “Bernie Nicholson’s Modern Motorcycle MechanicsBy Mike Brown

Here is thecomplete storyfrom Dec. 08Tip of theMonth

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42 February 2009 | WALNECK’S CLASSIC CYCLE TRADER® I WALNECKS.COM

Motorcycle Tips

bought, sold and servicedA.J.S., Ariel, B.S.A.,Matchless, Norton, RoyalEnfield, Panther, Sunbeam,Triumph, Villiers, and Indianmotorcycles. During WW IIhe served in the Canadianmilitary where his engineer-ing and motorcycle skillswere further honed andexpanded to include extensivecontact with Harley Davidsonmotorcycles, also well repre-sented in MMM. Nicholsoncontinued to operate a mail-order parts business until heretired in 1993 and finallypassed on in December, 2001.Every reference I’ve read orheard about Nicholson alwaysincludes “gentleman” andmany included “genius.”Perhaps the greatest giftNicholson possessed was theability to translate technicalprocesses into simple proce-dures, a gift one can reallyappreciate if he’s ever tried tofigure out a typical owner’smanual. Nicholson also pro-duced hard data where toomany others simply said things like“replace if worn” and for this reasonalone MMM is worth owning as areference source.

MMM is long out of print andoften goes for ridiculous prices onEBay. As of this writing, copies are

still available at British Cycle Supplyand if readers know of other sources,I’ll gladly pass this information on.Quite frankly, anyone who likes toturn wrenches on old motorcyclesshould try to get a copy while the lastones are still available. In the mean-

To measure bore wear, use the old piston and the top

ring. Remove the ring and position it using the piston

in the top of the cylinder, just slightly below the upper

most point the ring travels under operation. This is

where you’ll usually find the most wear.

If you can get a spark to jump with the ignition on but

the engine not running, the diode is leaking and must

be replaced.

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time, I’ll try my hand at evan-gelizing Nicholson’s wisdomstarting with a few of themany neat tips, tricks, andtechnical data he impartedover 763 pages. I’ll also try tosupply clear photographs, theone big flaw in Nicholson’swork and most likely causedby tenth generation reproduc-tions and a lack of space forphotography. I don’t knowhow many times I’ll dip intothis deep well, but here’s thefirst bucketful.

Bernie’s Brilliance Part I

Lucas alternator rotors are verydurable items if they aren’t demag-netized by connecting the batterycables backwards or by reverse cur-rent caused by a faulty rectifier.However, they do frequently sufferfrom a mechanical failure when thesteel insert loosens up inside of thealloy rotor housing. At one time, I’djust pitch the rotor, but according theNicholson, this isn’t always neces-sary: “Just a trace of backlashbetween the rotor and its hub doesnot necessitate replacement. This cansometimes be overcome by punch-locking.” (Seephotos for full details.)

Nicholson also has a super easy testfor the zener diode that does notrequire a single bit of test equipment.To test, simply turn the ignition on

and remove the connector to thediode. If bringing the connector closeto the diode causes a spark when themotor isn’t running, the diode is leak-ing and must be replaced. Nicholsonalso recommends using Locktite onthe diode threads because only 2 ft.lbs of torque should be used on theattaching nut. In absence of a tinytorque wrench, something Nicholsonrecognized as likely, he recommend-ed using a very small wrench andonly light pressure.

For the Algebra Impaired

Some older shop manuals used toinclude an algebraic formula for borewear. Only an old piston ring and aset of feeler gauges are needed fortools. Nicholson, as he does through-out his book on many procedures,simplifies the math considerably and

Measure the ring gap with a feeler gauge near the topof the cylinder and record measurement.

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provides a reliable means ofeasy measurement.

“Cylinder wear can be fair-ly accurately determinedwithout micrometer equip-ment by placing a piston ringin the unworn end of a cylin-der, measuring the gap with afeeler gauge and then shovingring with piston to the top endof the ring travel in the cylin-der and measuring the gap atthese two positions. The dif-ference measured at thesetwo positions will representapproximately three times thecylinder diameter wear.” Thistranslates into simple math.For example, a difference of.030 indicates bore wear of.010, beyond the maximumNicholson allows, .008, so it’soff the machine shop for arebore.

If you run this test on amotor teardown and find thebore wear within tolerances,Nicholson also has anothermoney and time saver when itcomes to deciding whether ornot to reuse the old rings.Nicholson says, “ Remove thetop ring from each piston, placesquarely in the lower end of thecylinder bore and check for gap. If inexcess of .030, ring replacement isadvisable. If gap is less, there isnothing to be gained by replacing the

rings and the remaining rings neednot be disturbed.”

So far, we’ve barely scratched thesurface of Nicholson’s vast wisdom.More to come in future installments.

Second bore measurement is taken at the very bottom

of the cylinder, where the piston rings never reach

and consequently where the bore is unworn.

Check the clearance between the ring and piston

groove with a feeler gauge as shown. If the clearance

is .007 or more, the piston is shot and must be

replaced. This one is at .004 and could be reused if

otherwise undamaged.

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