Cycle News - Archive Issues - 1970's

DOWN1E9N~J CYCLE CENTER M- eslODes All New Ready-to-Race Motocrossers Suzuki '74 TM75-$349. '73 TM250-$849. '73 TM4oo-$899. Maico Roo ials '74250-$1378. '74400-$139B. '74450-$1498. CZ '74 125-$895. '74250-$1149. '74400-$1249. '73 OSSA Stilleto $895. Super savings on all Suzukis from 50cc to 75Occ. 100% financing with approwd credit. Big, Big Year·End Clearance Sakt. Complete line ':)f parts and accessories for desert or motocross. Lay Away Now. from Downey area (213) B65-8223 from Long Beach (213) 431·1223 from Orange County (7141 521-5343 11835 E. Carson St., Hawaiian Gardens, Ca. 600 Feet East of 605 Fr_av, Carson-Lincoln off-ramp '!!!! ,_ 13347 W. Washington Blvd. (213) 390-3406 drive - features that _re pnwen It the Isle of Men TT. The foot shift_ soon to repI_ the then standlrd hlndshift. Send $3.00 for 256 colorful page catalog with more than 5500 items. ..... 0 • • The 1918 U.S.-built Indi..- introduced the three-speed glMbox end ell c:hIin By Geoffrey Wood COMPETITION SHOCK ABSORBERS • FIVE WAY ADJUSTABLE • • • • DISTRIBUTED BY CHROMED & POLISHED DOUBLE DAMPENING REBUILDABLE STREET OR RACING Sammy Tanner Distributing 734 No. Avalon Blyd. Wilmin~on, Calif. 90744 Phone: (213)83~ Setor Forks and Shocks Make the Difference B Jk-d~. "ot.re~ """Itlee 80Il 653. Chatsworth,' CalUornia 91311 Telephone \21Jj34)o..70 retail Boots-Motocross Style, sizes 3'h·10 '$64.95 Boou-Lace-up Style, sizes 5 to 10 59.95 B.W, Leathers, Be accurate about 72.95 measurements: waist, hips, thigh. inseam, calf. crotch to front of waist, crotch to back of waist. Any color or stripes. Jersey. - ex. sm, mad., sm .• lg. State 11.95 blouse .ize. Colors - Blue/White, Blk/White, Gold/Blk, Gold/Blue, . White/Red, Red/White. Gold Belt. - Deve Ekins kidney belts 16.95 fit all siz•. Scott Goggles - Polarized lens 15.95 Clear 11 .95 Gloves - MotOcross and desert stYle 12.95 Webco gloves, .izes 7 to 10 Waxed Enduro Suite Suit 64.95 Jacket 39.95 Pants 27.95 sizes ex. sma. 32-34 1m 34-36 mad. 38-40 Ig. 42-44 Bell Helmets - sizes 6'h to 7'% Super Magnum 49.00 - orange49.50 R-T 37.00 Bell Star. 120 full coverage 59.50 Make sure you tell me your exact girts' size in .hoe, glove, blouse size,because mistakes aren't necessary. Jim Davis MX equipment too. All orders UPS.cOD.lf you send chack or money order in advence I will pay the postage. GEAR FOR GALS I.... - 't, _ij\to'~~~. _: CyprftS. CA 90630 l71_1 827·7427 c:c:MtlTtTION MOTORCYCLE WHEELS DESIGNED. lUllT AND flIU .... "ED. SEND SOC FOIl CATAlOGl Mike Patrick's • YAMAHA of CORONA 1101 E. 6th St, - Corona (714) 735-7721 ,_..... _ ... ~ The modem motorcycle is a mechanical masterpiece. Sophisticated, reliable and capable of terrific performance, the contemporary motorcycle is a superb example of the designer's art. It has not always been that way, of course, since way back in the early days of motorcycling the bikes were primitive and unreliable propositions wi th mediocre performance. A multitude of technical improvements .have made the motorbike what it is today. In studying the history of the motorcycle and how it has evolved, it becomes apparent that racing and competition have had much to do with the perfection of the breed. Racing progress has been motorcycle progress, an axiom that is still with us today. Another element in the evolu tion of • the motorcycle is that the original inventor is not always the one who made an idea click. The really important person or comyany is the one who proved it could work. In the history of the motorcycle there are few ideas that have not been tried by some obscure designer in the dim dark past, and it was Dot un til someone proved the idea to the world that it was here to stay. In this, the first of two chapters, we will presen t some of the major inven tions that have helped make the· motorcycle what it is today, and in the second chapter we will present some of the less noticeable but equally importan t milestones of progress. Perhaps the best place to begin is with the engine, which way back in the early days of the century was either a side-valve design or the inlet-over-exhaust type. Having the pons in the block naturally restricted the "breathing" of the engine as weD as causing a great deal of heat and distortion problems, so it was only natural that many minds were working to overcome' these limitations. Side-valve engines transferred too much heat into the engine, and their performance naturally suffered. During the 1910·1920 era many new OHV designs were tried, some of which were as good as the best of the side-valve models. Out of aD this work there emerged one engine that was clearly superior, the 1920 AJS 350cc single. The new AJS featured pushrod operated valves, which were set at a 90-degree angle to each other, employing rocker arms. With a hemispherical combustion chamber, the advantages were space for larger valves, improved gas flow through the pons and a shon exhaust port that kept hea t from being absorbed into the head. The new AJS single was a smashing success, winning the 1920, '21, and '22 Junior IT races in the Isle of Man as well as a vic tory at record speed in the 1921 Senior IT. This achievement with only 350cc is the only time such a feat has ever been accomplished, which shows just ho superior this new design 'n Je can thus be reall • w' . The \ I called Inc Ul 0 .. e mr ci m OHV engine. Th e next milestone in engine development occurred in 1926 when the Velocette concern garnered the Junior IT trophy at record speed. The new single had an overhead camshaft head, and it was the first IT win by this type of design. The valves were opera~d by short rockers, with a vertical shaft and two pairs of bevel gears driving the camshafL The advantage was a more reliable engine capable of higher RPM. The Velocette singles were steadily developed, with more IT wins in 1928, '29, and after the war in 1947, '48, and '49. The company also dominated the 350cc class of grand prix racing from the late 1920. to 1951, at which time the factory lost in terest in racing. The 1926 Velo was thus the father of many superb OHC engines since that day, which all display the virtue of reliability at high engine speeds. Another milestone in OHC design was the 1937 Nonon works singles, which featured a double cam design that dispensed with the rocker arms and thus Iigh tened the valve gear even more. This practice has been used on virtually all racing engines since that time, and then in 1966 Honda became- the fllst to use the idea on a roadster engine with the introduction on the 450cc DOHC twin. The other half of the engine development story is more recent but also more dramatic. Up until the 1930s the two-stroke design was considered to be a very inferior proposition used only in inexpensive utility bikes that had a mediocre performance. The German DKW concern was struggling with the two-stroke then, both in roadster and racer form. The racers weren't very successful, mainly because the raised edge on the piston crown distoned when it heated, with the result that the piston would freeze up in the bore. The answer came in 1934 when Dr. Schnurle invented his loop scavenging design in which the transfer pons were located near 'the front of the cylinder and inclined upwards. This piston crown was left nearly flat, so that the incoming fuel charge could cross the piston crown, travel up the back walls of the cylinder, over the top of the combustion chamber, and then down the front wall and out the exhaust pOrL The advantages were a flat piston crown that expanded evenly and did not freeze up, less fuel charRe lost out the

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