Zun­dapp 100 Mini mus­cle

Zün­dapp went from pre-war flat twins and fours to post-war tid­dlers. But all were pro­duced to the com­pany’s most ex­act­ing stan­dards.

Old Bike Australasia - - CONTENTS - Story Trevor Byrne Pho­tos Jim Scays­brook

Of­fi­cially known as the 100 GS, Zün­dapp’s lit­tle gi­ant killer gained its show­room ti­tle fol­low­ing sev­eral years of suc­cess in the Olympics of mo­tor­cy­cling, the In­ter­na­tional Six Days Trial. In that con­test, myr­iad small ca­pac­ity classes, from 50cc up, re­flected the mas­sive buyer mar­ket for such ma­chines in Europe. From 1963 to 1969, the six-rider East Ger­man squad col­lared the In­ter­na­tional Tro­phy six times (beaten only by West Ger­many in 1968). The West Ger­man vic­tory was achieved with the en­tire team mounted on works-sup­plied Zün­dapps, from 75cc to 125cc. Re­put­edly, these mo­tor­cy­cles were uber-tuned and fit­ted with six-speed gear­boxes – the 100 poked out 14 horse­power. As well as the need for out­right speed, the ISDT also placed strict re­quire­ments of re­li­a­bil­ity. Mo­tor­cy­cles had to be street le­gal, their light­ing fully op­er­a­tional, and fin­ish the event equipped with the same parts they started, save what the rider could carry in his pock­ets (or what could be se­creted in the forests and fit­ted out of sight of of­fi­cials). But key com­po­nents such as wheels, frames and even en­gines were marked with spe­cial paint, so any skul­dug­gery was usu­ally con­fined to less vi­tal parts. The clam­our for an ISDT replica Zün­dapp was deaf­en­ing in Europe, and it gained con­sid­er­able trac­tion in the US af­ter the leg­endary Bud Ekins on a 100cc Zün­dapp thrashed the field (which in­cluded 360 Husq­var­nas, 650 Tri­umphs and 500

Match­lesses) to win the pres­ti­gious Green­horn En­duro in 1967. That win changed the sta­tus quo in the US for­ever. No longer stood the adage, “There’s no sub­sti­tute for cu­bic inches”. In­stead, “power-to-weight ra­tio” quickly be­came the buzz-phrase. When it came to pro­duc­ing a cus­tomer ver­sion of the Zün­dapp ISDT win­ners, things changed a bit. The new-for-1969 100 GS boasted 9.3 horse­power (still very re­spectable for such a minis­cule en­gine) and used a gear­box with just four ra­tios. How­ever in most other re­spects, the Replica was close to what the stars were us­ing, re­sult­ing in a ma­chine that tipped the scales at just 84 kg, ready to rumble. That fig­ure in­cluded a very com­pre­hen­sive tool kit that was at­tached to the fuel tank by sub­stan­tial straps. The kit con­tained car­bu­ret­tor jets, Ger­man-qual­ity forged span­ners (no prissy lit­tle stamp­ings here) and two spare coun­ter­shaft sprock­ets, each one tooth ei­ther side of the stan­dard 15 tooth job. Un­like the works mod­els, which car­ried a com­pressed air cylin­der for rapid tyre in­fla­tion, the Replica was sup­plied with a fairly flimsy plas­tic hand pump.

Heart of the mo­tor­cy­cle is the all-al­loy pis­ton-port two stroke sin­gle, which looks a lot larger in ca­pac­ity than it ac­tu­ally is, thanks to the gen­er­ous finning on the bar­rel and head. The bore of the bar­rel is chromed, and all ma­jor bear­ings are ball, roller or nee­dle roller. Bore and stroke are square at 50mm x 50mm, with a com­pres­sion ra­tio of 9.0:1. The mo­tor breathes through a 22mm cen­tral bowl Bing car­bu­ret­tor, which draws its air through a size­able pa­per fil­ter lo­cated be­neath the seat, which is en­closed in the up­per sec­tion of a large in­jec­tion­moulded plas­tic box. The lower sec­tion of this box acts as a still-air cham­ber and in­take si­lencer be­fore the air reaches the car­bu­ret­tor via a long flex­i­ble hose. The ex­haust sys­tem was care­fully de­signed to de­liver max­i­mum torque and power, and the fac­tory bul­letins warned that re­mov­ing the muf­fler would re­sult in a dra­matic re­duc­tion in both, as well as a lot of un­nec­es­sary racket.

There is no fat in the chas­sis depart­ment ei­ther. The en­gine is sus­pended from the large di­am­e­ter tubu­lar steel back­bone struc­ture by a strange look­ing Y-shaped bracket that at­taches to the top of the crankcases and runs to a bracket un­der the rear of the fuel tank, which it­self holds 12.5 litres of pre- mixed oil and petrol. The en­gine is fur­ther se­cured to the frame by a box sec­tion bracket ad­ja­cent to the swing­ing arm pivot, with a tubu­lar sump guard run­ning all the way to the gear­box. The seat, rear mud­guard and rear sus­pen­sion mount on a tri­an­gu­lated se­ries of tubes which are no thicker than they ab­so­lutely need to be. Again, un­like the works bikes, there is no cen­tre stand, only a side stand with a big foot for some de­gree of sta­bil­ity in soft ground. Prob­a­bly in the in­ter­ests of pre­serv­ing crankcases and gear/brake levers, the footrests do not fold; rather, they are made from im­mensely sturdy tubu­lar steel with equally im­mense mount­ing brack­ets. From the days where the new­fan­gled Ital­ian and Span­ish forks of­fered around 170mm of travel, the Replica has just 100mm from the Zün­dapp-made tele­scop­ics, the same as de­liv­ered by the Boge units on the rear end. But with such light weight to sus­pend, this is prob­a­bly all that’s nec­es­sary. Road tests of the day had few com­plaints, other than the long gear change throw that re­quired rid­ers to lift their foot from the left footrest when chang­ing from first to sec­ond gear. What came in for uni­ver­sal praise was the im­mac­u­late han­dling, which got bet­ter as you went faster. Even in the US, where the trend had al­ways been to use 19-inch tyres on the front end, testers raved at the way the puny 2.50 x 21 front hoop sim­ply skimmed over any­thing in its path. Cou­pled to the 3.50 x 18 rear, the han­dling was usu­ally de­scribed as noth­ing less than per­fect, de­liv­er­ing “an un­canny abil­ity to for­give the blun­ders that are usu­ally com­mon in of­froad sor­ties”. Even the tiny brakes – just 120mm sin­gle lead­ers front and rear – were deemed per­fectly ad­e­quate for the job. Again, a case of no ex­tra weight where it was not re­quired. Be­cause of lo­cal reg­u­la­tions, US Mod­els were sup­plied with a bat­tery, whereas Euro­pean and Aus­tralian mod­els ran light­ing di­rect from the

fly­wheel mag­neto. In 1968, the Zün­dapp was on the mar­ket in Aus­tralia for $499; not ex­actly cheap but not too scary for a ma­chine with such an il­lus­tri­ous pedi­gree. And in those fledg­ling days of ‘trail bikes’, which usu­ally meant Bul­taco Mata­dors or the new DT1 Yamaha, the lit­tle Zun­dapp could more than hold its own in any con­test, as Bud Ekins had demon­stra­tively shown.

RIGHT The lion-hearted en­gine looks big­ger than its 98cc due to the ex­ten­sive finning on head and bar­rel.

Bare min­i­mum switch gear. The seat is de­signed to pro­vide back­sides with re­lief over Six Days of pun­ish­ment. Lugs on the top of the fuel tank are for the tool box mount­ing straps.

En­gine is sus­pended from an un­usual Y-shaped bracket.

A GS125, the later 125cc ver­sion with ra­dial fin head and much larger brakes.

LEFT By all ac­counts, the lit­tle Z will wind its speedo nee­dle around to the stop. RIGHT Footrests are ex­tremely ro­bust. ABOVE CEN­TRE Tubu­lar steel net­work fends off the boul­ders. ABOVE LEFT Puny look­ing brakes ap­par­ently work en­tirely ad­e­quately....

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