Honda XL250 Trail­blazer

Old Bike Australasia - - CONTENTS - Story Jim Scays­brook and Tim Mar­gin Pho­tos OBA ar­chives and Tim Mar­gin.

Check the spec­i­fi­ca­tion of any mod­ern 250cc en­duro or mo­tocross mo­tor­cy­cle (and many road go­ing 250s) to­day and there is a cer­tain sim­i­lar­ity – all sin­gle cylin­der, dou­ble over­head camshaft, four-valve. Just like the Honda XL250 of 1971. Sure, wa­ter-cool­ing is uni­ver­sal whereas the Honda used good old air, and twin cams re­place Honda’s sig­na­ture sin­gle camshaft, but oth­er­wise not much has changed.

In the dirt bike boom that be­gan in the late ‘six­ties, Honda got ham­mered, mainly be­cause the com­pany’s ethos was four stroke tech­nol­ogy, and vir­tu­ally all the op­po­si­tion was two-stroke based, not least be­ing the ground-break­ing Yamaha DT1, the mo­tor­cy­cle that brought trail rid­ing to the masses. But Honda wasn’t ready to aban­don its prin­ci­ples, not yet any­way, and qui­etly plugged away in the de­sign depart­ment while oth­ers racked up im­pres­sive sales fig­ures. Along the way, Honda re­fined what were es­sen­tially con­verted road bikes (the CL se­ries) into more dual-pur­pose mod­els, of which the SL350 was the first de­cent at­tempt and in ret­ro­spect, wasn’t a bad bike at all, al­beit over­weight. There was also the fine line of lit­tle off-road­ers, namely the Honda SL125 sin­gle (which ac­tu­ally won a Gold Medal in the 1972 In­ter­na­tional Six days Trial rid­den by Amer­i­can Leroy Win­ters), but what was des­per­ately need to com­pete with the DT1, and to a lesser ex­tent the Suzuki Sav­age (plus the Span­ish Bul­taco, OSSA and Mon­tesa) was a proper 250 sin­gle that was as com­fort­able in the dirt as it was on the tar­mac. In Jan­uary 1972, it all came to pass, when Honda fi­nally pulled off the wraps of its XL250 Mo­to­sport at a dealer con­ven­tion in Las Ve­gas. The XL250 owed noth­ing to its pre­de­ces­sors, it was all-new, as was the XL des­ig­na­tion that was des­tined for a long life. Honda did not ap­pear to be overly wor­ried that up till now, XL had been firmly iden­ti­fied with the Har­ley-David­son Sport­ster lin­eage. Un­like pre­vi­ous Honda prac­tice, the new engine was way over­square at 74mm x 57.8mm bore x stroke, cre­at­ing an engine that was not overly tall – a char­ac­ter­is­tic of most but not all four stroke sin­gles with their bulky cylin­der

head struc­tures. The big bore also meant a big com­bus­tion cham­ber, and us­ing sin­gle in­let and ex­haust valves would have meant these items be­ing weighty. Ad­di­tion­ally, it would have re­quired long and also heavy rocker arms to reach the valve tips, both of these fac­tors lim­it­ing the engine’s abil­ity to rev freely. Honda’s an­swer was to uti­lize its vast ex­pe­ri­ence in rac­ing, and to use four valves in­stead of two. This meant lighter valves that soaked up less heat, and shorter, lighter rocker arms op­er­at­ing them. Ad­di­tion­ally, the spark plug could sit where its flame travel was at its op­ti­mum, right in the cen­tre of the com­bus­tion cham­ber. All this tech­nol­ogy comes at a price of course – the tra­di­tional tus­sle be­tween the de­sign en­gi­neers and the ac­coun­tants – but Honda man­aged to keep the peace. The two-lobe camshaft it­self was very short and driven from the crank by a con­ven­tional chain. A sin­gle rub­ber-mounted 28mm Kei­hin car­bu­ret­tor was used with twin ca­ble op­er­a­tion for the round slide, feed­ing a sin­gle in­let port which split in­ter­nally to feed each in­let valve. Honda also paid par­tic­u­lar at­ten­tion to air fil­tra­tion, feed­ing air through sev­eral stages into a box con­tain­ing an oil-im­preg­nated polyurethane foam sock stretched over a fine-mesh stain­less steel base. With the knowl­edge that a goodly pro­por­tion of XL250 pro­duc­tion would end up churn­ing through Cal­i­for­nian desert trails, this at­ten­tion to air pu­rity was well founded. On the ex­haust side, both ports from the ex­haust valves Si­amesed to a sin­gle 30mm out­let with a high level ex­haust pipe lead­ing to a fairly vo­lu­mi­nous muf­fler with a small sin­gle out­let on the up­per edge. Within weeks of the XL250’s re­lease, sev­eral man­u­fac­tures were hard at work on af­ter-mar­ket ex­haust sys­tems, and although in­vari­ably louder than the stan­dard item, few were any more ef­fi­cient. Other as­pects of the power-plant were fairly con­ven­tional, with a fly­wheel al­ter­na­tor on the left end of the crankshaft with the con­tact breaker and auto-ad­vance up­stairs on the end of the camshaft. The crank it­self ran on roller bear­ings, with pri­mary trans­mis­sion by straight-cut gears to the five-speed gear­box and seven plate clutch. A high-ca­pac­ity tro­choid-type oil pump forced oil through­out the engine and gear­box, with in­ter­nal screen and cen­trifu­gal oil fil­ters to re­move im­pu­ri­ties. Visu­ally, the engine’s unique fea­ture was the use of die-cast mag­ne­sium al­loy for the outer engine cov­ers, which were fin­ished in a unique shade of grey/green. The en­tire engine/trans­mis­sion pack­age was an ex­er­cise in com­pact ef­fi­ciency, and looked lit­tle larger than the two-stroke sin­gles it was in­tended to take on in the show­rooms. Like the engine, the XL250’s chas­sis was all-new; a con­ven­tional sin­gle front down-tube frame split­ting be­low the engine to form a cra­dle that then housed the swing­ing arm pivot. Up top was a large di­am­e­ter back­bone tube run­ning down to the rear engine mount, the tube dou­bling as the oil tank. For a 250, the frame it­self ap­peared to be overly engi­neered and ex­ces­sively heavy – a point not lost on sev­eral US frame mak­ers who quickly drew up lighter and bet­ter han­dling ver­sions. Up front sat a set of forks that used a new-for-Honda style of damp­ing, sim­i­lar to the Ital­ian Ce­ri­ani cen­tral pis­ton sys­tem, with rear dampers each car­ry­ing two springs of dif­fer­ent wind­ing and five-way pre-load ad­just­ment. Cu­ri­ously, the rear shock had two up­per mount­ing po­si­tions, the for­ward one about 50mm from the rear and slightly lower. Honda also aban­doned its tra­di­tional full width hubs for new con­i­cal shaped items. The front had an alu­minium brake drum, with a steel spoke car­rier riv­eted to the flange on the right hand side, while the rear was a spool type with a built-in rub­ber shock ab­sorber. Both wheels car­ried a new style DID shoul­der­less alu­minium al­loy rim; 21 inch front and 18 inch rear. Both mud­guards were of light­weight flex­i­ble plas­tic, with a steel fuel tank and a steel base for the seat.

With dura­bil­ity a strong con­sid­er­a­tion, there was no way the XL250 was go­ing to match the twostrokes in the over­all weight depart­ment, and ready to roll, the weight was around 130kg, or around 20kg more than its arch ri­val DT1 Yamaha. The XL250 came with ad­e­quate light­ing, turn in­di­ca­tors and in­stru­men­ta­tion via sep­a­rate speedo and tacho.

All these com­po­nents could be quickly re­moved for week­end club rac­ing. The seat, while ba­si­cally de­signed for one per­son (rear footrests were fit­ted as stan­dard), was wide and plush. In Aus­tralia, the new XL250 was re­ceived with enor­mous an­tic­i­pa­tion and trans­lated into in­stant suc­cess on the show­room floor. As al­ways, the bu­reau­crats fid­dled with the stan­dard spec­i­fi­ca­tion, which meant a lower front mud­guard had to be fit­ted be­fore the ma­chine could be reg­is­tered in New South Wales. A ma­jor en­tice­ment for the two stroke rid­ers was the XL250’s in­cred­i­ble spread of power, pulling smoothly from 1500 rpm with bags of us­able torque in an engine that also had a healthy ap­petite for revs. Deal­ers were soon clam­our­ing for more stock – the XL250 be­came one of the big­gest sell­ers in the range. Just one colour was of­fered; sil­ver with con­trast­ing ma­roon and black strip­ing. The ba­sic model re­mained in pro­duc­tion un­til 1985, an in­cred­i­ble run and a tes­ta­ment to the sound­ness of the orig­i­nal de­sign. More than a few XL250s quickly found their way onto the track, as well as in the grow­ing sport of En­duro. The quickly re­mov­able lights and in­stru­ments meant the XL could be rid­den to the track and quickly stripped for ac­tion. The front fork stan­chions could be slipped up or down in the steer­ing crowns which helped in Short Cir­cuit rac­ing. The XL’s slight weight penalty worked against rid­ers in mo­tocross, but that didn’t stop quite a few try­ing. Not sur­pris­ingly, a huge range of af­ter mar­ket parts sprang up; ex­haust pipes, car­bu­ret­tors, air fil­ters, mud­guards, com­plete frames, and in­ter­nal parts such as valve springs, camshafts and big-bore kits that took the ca­pac­ity be­yond 300cc. Even with the boosted per­for­mance, the orig­i­nal bot­tom end rarely gave trou­ble, although one hitch that showed up in com­pe­ti­tion was a ten­dency to break the gear­box main­shaft un­der ex­treme go­ing, some­thing that never af­fected the bike on the road.

MAIN/ABOVE Tim Mar­gin’s re­stored XL250 at the Tam­worth Look­out dur­ing the 2018 VJMC An­nual Rally. Orig­i­nal Honda XL250 brochure ex­tols its virtues.

ABOVE Mo­tocross stars Roy East (1) and Brian Martin in close com­pany on XL250s at the Ama­roo Park cir­cuit in Syd­ney in 1972. East’s bike has the NSW regis­tra­tion low front mud­guard. TOP LEFT Cylin­der heads un­der pro­duc­tion in the Honda fac­tory, with an XL250 4-valve head in cen­tre of photo. LEFT Fresh off the pro­duc­tion line; a batch of XL250s at the Honda fac­tory in 1972. A re­stored XL250 owned by VJMC mem­ber Graeme Dust­ing.

LEFT A lo­cal ad for the XL250 from 1972. The man per­form­ing the jump is Ben­nett Honda NSW Sales Man­ager Ge­orge Pyne, who was a handy scram­bles and dirt track rider.

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