We'll give you the chance you didn't take at school.

'O' level standard in Maths, and Science or English, could get you a great career in today's Navy. We'11 tr ain you to be one of our top technicians, working on space-age equipment and earning £2,000 a year at 24. If you're 15{--17 -} send for our free book. ,----------

APPRENTICESHIPS Name

Address

Dote of birtlt

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(Enquiries fr om U .K. re sid ent s only) Royal Naval Careers Service ( 629QN I), Old Admiralty Bldg., WhitehaU , RBI LondonS .W .1. P icas : se nd me , with out obliga toon, your free booklet, "Royal Navy Technician Apprentice-ships". •

1_ _________ ROYAL NAVY

NOW! Centurion X goes racing!

with the new GT polycarbonate helmet to BS1869,Z90.1 N.Y.

Q

208 Motorcycle S port , lun e 1971

&approved · · by (I A.C.U. ~ .

~ 0 \ ... 0 ,~ all the Centurion X

~ features for only

£6 PLUS25p for A.C.U. label

See the Centurion X GT. at your local dealers NOW. Or send coupon for details ~--~--------, Send this coupon for leaflet. · I Please send me details of the Centurion X GT. I

I Name ·

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THETFORD MOULDED PRODUCTS LTD. THETFORD, NORFOLK. l ___________ ,,,,

TRACK IMPRESSIONS AT SILVERSTONE

Sondel Sport Grand Prix 125 LATE last yea~ when we tested a Yamaha YASI 125 ro ad bik e we said that we would be very glad to try a racing ver sion. Soon after­ward s a lcller appe ared at Standard Hou se offerin g u s the oppor­tun ity to tr y such a ra cer. Sonde l Sport are well kuowu for th eir extensive Yamaha spare s cove rag e, and for th e last seaso n th eir nam e has be en seen on ra ce mee tin g programm es, when their Sondel Yamaha, in the hands of Grant Gib son , r eac hed ninth place in th e 125 c.c. Champion ship in the first seaso n of Sondcl Sport ' s intere st in spon sorship.

We saw Mr . Ja ckson, director, and Spares Manag er Ron Ba yli ss on the Sondel stand at th e Show at the Horticultural Hall in January , and we agre ed to wait until the weath er improved befor e ll'yin g out their new machin e, built over the wint er. We wer e very glnrl to receive th eir offer, and when the sun b egan lo fight th e sn ow and frost on more equal term s we arnmgcd to carr y out th e

Motorcycle Sport, June 1971 209

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T he £130 GYT kit mark eted by Sondel boosts the 125's power to 22 b.h.p., giving over 100 m .p .h.

210 Motor cycle Sport, Jun e 1971

test at Silverstone durini:: on e of th e pra c­tice day 's run there by th e Sou th er n Six ty Seven Ra cing Club . Early in Mm·ch , at the first session of th e Dixon-Robb Ra cing School, Silver ston e wa s iu fine and fr eez ­ing form, with snow flurri es throu ghout the day. Bitt er it wa s : and I am delight ed to say that thi s SSRC pra ctice session wa s on a fine anrl warm day in April. No t a sign of rain , sun all clay, and the tra ck in good con dition.

Earl y in the clay I r eac quainted myself with the Clu b Cir cuit on m y own ma chine and r estored my shak en belief th at (even with the help of an unfairl y tra ctable 54 b .h .p. ) I was unabl e lo ge t ro und in under 1 minute 20 sec ond s . After the rapid progre ss round th e cir cuit by the Racing School pupil s m y mora le h ad be en thoroughl y low ered , and some thera py seemed to be esse ntial before try in g to do justice to a Rea l Racing Machin e . Moral e restor ed, the Son d el van arrived with Grant Gib son' s F iat on it s h ee ls. The Sondel Yamaha that I was lo tr y wa s the machi n e of th eir front runner , Grant Gibson, and had th e full benefit of a season' s dev e lopm ent bu ilt into th e engine. Th e Yamaha GYT Kit claim s a power band of 8'/:i-111h k. r .p .m.: the Sonde l has a band from 111,4-131,4 and , alth ou gh no figures ar e e ith c1· known or claime d, it is pretty clear th a t some real improvem ent s in power deliv ery have been achieved.

The 1971 ma chine ha s a complete ly new frame, new brake s, and th e hard-won engine tweaks applied to a n ew engine fitted with a fre sh GYT Ki t as a ba sis. The ma chin e h as had four ra ces so far in this year, achi ev in g two sixth s, a fifth and a non- sta rt. The engine is pretty well sorted out now, but for a starting prob­lem that i s caus ing some conce rn a t present: the main att ention is dir ec ted towards th e handling, steering and sus­pens ion in ord er to get the new cha ssis and running gea r in to a fully effective

DISC BRAKES

tune. From the beginning tl1e handling lo oked po tentially good, but the rea r sus­pen sion was far too hi gh with the shorte st Gir lin gs availab le. Thi s was qui ckl y cured by using a set of very comp act Koni unit s, and th e spr i111; rat e is being pro­gress ively redu ced. From my ride s I would judge that the rate could be cut down a fair bit more, and it is in tere sting to n:>te that I am havin g precisely th e sarne " pr ob lem" with the Konis on my own machin e.

The Son del frame is built out of T45 tubing (lin diameter) and finished in n ickel plate. It is a doubl e-cra dle frame wi th pl entiful bra cing to the steering head , and a solid and ri gid pivot point for the swinging arm. The swinging arm is built fr om D-section tubing , and has whe el udju stment fitting s at either end. On th e ma chin e I tried it was at the rear end . Th e whe elba se is 53in for the 125 unit and 54in for the 250/ 350 unit s. The overall wei ght is 25 lb , and nickel plate fin ish is a stiff £15 sur charge over th e ba sic £80 price of a finished fr ame. The gla ssfibre u sed on the Yama ha is all Sond el equipm ent. The sea l and fair ­ing are simply suitable and well-fittin g exurnp les of a rather regime nt ed bre ed, and the lank unit is a neat and well­thou ght-out unit with a fuel colle ction sump and amp le capa city.

Disc brakes The mo st int ere stin g featur e of th e run­

n in g gear is the u se of mechanicall y­opera ted Cnmpagnolo di sc brak es on bot h fr on t and re ar hub s. Th ese unit s are fitted lo th e 600 MV road bike , and proved well up to th e job of stopp in g Nige l Mead' s side car outfit when tri ed dur ing the 1967 season. Campagnolo di scs have been appea rin g on man y 50 and 125 c.c. ma chin es s ince then, but I have never tried them. The price s are no I at all unreasonab le: £50 for a front hub with twin di scs and callip ers, and the same for

the single-di sc rear hub with sprocke t and integral rubb er damper . Both the se are fitted to th e Sondel Yamaha and the front twin di scs are ope rated b y a comp en satin g lev er. Thi s is al so a Campagnolo part , and u ses a balan ce whee l to op era te a single cable allached to the two calliper arm s. The action is via a worm actuated by tl1e normal movement of the actuating arm, with no other servo ac tion.

Th ese d iscs are neat and light and hav e a very different feel fr om the hydrauli­cally -actuated systems wh ich I have u sed before .

The other Sonde l modifi cations to thi s ma chin e are over-size carbur ettor s, Dut ch straight- cut prim ary gears ana Du tch close-ratio five-spee d gearb ox. Th e com­bination of rai sed bottom r atio in thi s box and the lowered gas speed tl1rough the enla r ged carbure ttor s is p robab ly the reason for the curr en t starting difficultie s. A mo st impr ess ive array of NGK plu gs is being steadily tried out, but the key has not yet been found. It would be as well lo point out that all th ese comments r efer to th e spe cia ll y-tun ed machine ridden by Grant Gib son, and not to th e " Grand Prix " 125 sold by Sonde l wi th all the same chass is and running gear, but short of the more extreme twea ks.

Th e first spell on the tr ack was taken by Grant on th e Yamaha to check that all was well: I follow ed on th e Hond a lo see how the Yamaha went. It was rapidly shown that th e little Yamaha accelerated very fast indeed and h ad a top speed with a safe and hon est margin over th e 100 mark . It was al so clear tha t tbe Maggot s ripple s wer e up settin g the Yama ha, and that it was jumping about a l ot . From a close rearward view of tl1is action it seemed that tl1e sprin g ra tes wer e lo blam e, as no frame troubl es seemed to b e appar en t .

Wh en we pull ed in, I was warned th at tl1e Yamaha was und er geared for the cir ­cuit as it was easily pullin g th e 131h k .

SONDEL SPORT

ALL NEW ROAD MODELS

FROM STOCK

1 Stapleton Hall Road, LONDON, N.4. Tel: 01-272 6522

SONDEL YAMAHA Grand Prix 125 c.c. £560 SON DEL YAMAHA Clubman Racer from £375

S.A.E. for full details of Racing and

Customising Equipment.

POSTAL SPARES BY RETURN

SERVICE & PART EXCHANGE ON ALL MODELS

PERSONAL EXPORT ARRANGED FOR OVERSEAS VISITORS

Motorcycl e Spor t, Jun e 1971 211

f ,

peak r .p.m . allowed. Thi s mea nt that the 14 k. reel line was of eq ual import· ance in all th e gears, and as thi s mark is set by th e fact that the big-end s look upon 14 k. as the signal to give up and go on strike in short order , there was no ques­tion of bu zzin g it in any gear for any rea son . With th e unfiddled GYT Kit this provi so clearly does not have so mu ch for ce .

Grant and I then switched ma chine s and I squall ed off to come to term s with the 125 and the circuit in my own tim e. Being a rank coward, the se firs t few lap s wer e sp ent demon strating how kind ly the tuned 125 could be to tho se mi sguid ed enough to ask it to run from 9 k . r .p.m . The power at the r .p.m. was ad equat e to give so me (po or) acce lera ti on until 11 k. was r eached : from th a t point the power d eliv ery was equall y smooth hut the accele ration was excellent. The gear ratio s m atched th e breadth of th e pow er band to a ni cety and the gear- change it se lf was of minimal mov ement and un­failingly po sitive action. Not once did I fail to u se th e clut ch for all gear changes : p erhap s unn ecessa ry, but cert ainl y kind er to th e gea rbox, and as I was hardly in­te res ted in squeezin g the las t split second from the lap tim e in th ese tr ack impr es­sion s, it could r ead il y he avoid ed.

Th e stee rin g was be autiful. On e merely · had to thin k th e Yamaha on to a line : th e re wa s n o pit ching or twit ching any· where but at Maggots , and th e frame geo­m etry and ri ding po sition gave a weight di stribution th a t effec ti vely stopp ed any wh ee li e action or stepping out on cu rves. The ground clearance wa s nev er r eall y ex pl oit ed in my ridin g, as a judi cious safety ma r gin for avoiding ac tion , and any other un exp ec ted eve nt s. I soon con­firmed th a t the geari ng was too low for Si l ver stone, as I could get 13 'h k . on the st r aig ht eve n sittin g up behind th e fair· in g. As I bulged out all over the Yama ha anyway I d oubt if my sittin g up made mu ch diff eren ce to th e fr ontal area: or so I was acc urat ely - if unkindly -inf orm ed!

The action of the Campagno lo brak e did not me et my full approval. Th e me chani cal di scs h ad a wooden feel and were r ath er in sensiti ve in acti on, I th ou ght. Lig ht pr essur e didn ' t do mu ch and ju st a littl e mor e pr oduce d too muc h . It 's a q ues tion of se nsitivity and I neve r rea ll y got to tr us t th e brakes and my h and s to deli ver pre cisely th e amount of reta rdin g power needed at any given time. For pure pow er th e Campag nolo b rake s wer e excell en t: I'd ju st r ather have a wid er ra nge of eas il y-ap plied l evels of re tar dation.

By th e tim e I had go t on term s with th e co mpa ct riding position , th e fee l of the brake s and th e pow er chara cter istics of the en gin e I was beg in nin g to tak e more not e of the handlin g, and at steadi ly l1igh er sp eed s I go dow n to findin g out more about it. Maggot s bend was the R u bi can an d th e Ya maha ch opp ed its way acro ss th e ri pp les in a pr edi ctabl e- if h a ir-r ai sin g- serie s of colti sh arcs. A fter

212 Mot orcycle Sport, June 1971

several lap s I was inclined lo bl ame the rear- suspen sion sprin g rat es but, know­ing the de cepti ve cussedne ss of thi s sta ge -0f sorting out, I'll accep t bet s on the ba sis that it's really the front end that 's too stiff- I 'd have Grant Gib son' s mon ev on that, anyway-and on thi s point Gran·t mention ed that the Honda was handlin g better than the Yamaha al thi s point on the circuit, and at about thi s point in time he stopped foll owing the Rabbit and cleared off at a great rate of knot s.

A littl e later the engine falter ed as I reached 121/i k. in top down the straight : my well- edu cated Two-Stroke Reflex took over and I whi stled in to the Paddo ck on a dea d engine with tJ1e clut ch out. With vision s of having to say " It ju st came away in me 'and, Mister ", I was glad to he ar that it was a question of no fu el.

After topping up, I returned to th e cir­cuit to see ju st how hard it was to drive on such a narrow power hand and mak e be st use of it. I came to the conclu sion tliat it would take a fair whil e befor e it could becom e sufficiently au tomati c for me to ha ve that and racing, too . The for­giving deli very of power at 111h k . would help no end in pra ctice and, in spite of my comm ent s, I feel that the 125 Yama ha is a suit abl e machine for a novi ce ride r (prefer ably ph ysicall y small er than my· self ). After all, even I managed to gel round in lm 24s in my cautiou s way. The engine is a real pl easur e to use , smooth an d cri sp, th e brakes have am ple power and need onl y an educated right hand , the fram e seems to be a good one , and spare s are plentifull y available. Son· del claim to maintain 100 per cent cover­age of 125 parts and racing bit s, and sell all the item s of the GYT Kit separately if req ui red.

Routine maintenan ce on the Sondel Sport machine is simp le. Th e heads are lift ed after each meeting and the crank changed at every six. The key it em is the maintenan ce of accurat e timing for the i gnition : thi s is che cked and rese t after every ra ce by the odd th ou to keep the engin e on top tun e. Alt hou gh th e crank cos ts abo ut £24, it is possibl e to do a compl ete overh aul for a bit over half thi s, and the figure of six meetin gs is one for prevent ati ve maint enance rath er than an essen tial guide. Th e part s arc not very exp ensive and here arc some examp les :

Poi nts, £1.50; racin g con.-rod s, £3.69 ; cra nk shaft seals, abou t 20p; gearbo x spro ckets, £1.31; labyrinth seal , 54p.

Speci fica tions of the GYT Kit and th e Sondel Yamahas are given here : G YT Kit (£130)

Exp ansion boxe s, barrel s, h ead s, p iston s, rin gs, car burettor s, clutch plate s and springs, convers ion gear s, mag neto, carbur ettor spanner s, few othe r sundri es.

R esull s Maximum pow er 22 b.h.p. at 12 k.

r.p.m. Max imu m torque 1.82 kg-m. / 111/i k.

r .p .m. Maxi mum spe ed over 100 m.p.h. Compress ion ratio 7.9: 1.

Ignition timin g 2111111 b .t. d .c . Mixture 15: 1 (remov ed aut olube ), 20: 1

( +autolub e). S0 11del Clubnum 125 (£375)

Weight 190 lb appr ox im ate. Thi s is a co nv ert ed YASI +G YT Kit

So ndel Gra nd P rix (£560 with ni ckel­plat ed frame). So nclel frame as desc rib ed in thi s article, MP 600 fork s, Ca mp ag nolo di scs fr ont and rear. Yama ha GYT Kit , full -ra ce gla ssfibre, e tc., equipm ent . Weight 170 lb approximat e.

Sond el de scr ibe the Cluhm an as ju st that and , I think , fairl y : the y desc rib e the Gr an d Prix as a ma chin e for national and int ernational classes, and with con ­sistent top -six placing s thi s sea son and last, Grant Gib son i s proving th em corre ct.

Th e m achin e describ ed in thi s article is a tun ed ver sion of the Grand Prix and I should like to thank Ron Bayliss and Grant Gib son for their tim e and troubl e in helping to carry out thi s tes t, and Mr . Ja ckson of Son del Sport for th e opp or­tunity to u se th e ma chin e. M. R . W.

GUS KUHN NORVIL DISTRIBUTORS

GUS KUHN Motor s of London , SW9, announce th a t th ey ha ve b ee n uppoint ed officia l di stributor s of Norv il perform­ance eq uipm ent. Th is ran ge of speci al compon ent s has been design ed and manu­factur ed by No rt on Villi ers for th e Com ­mand o mod els . Gu s Kuhn Motor s carr y a complete stoc k of thi s equipment and offer new Comm ando s fitt ed with any, or all , it ems to order. Commando engine s, we are inform ed , ca n n ow also be accep ted for preparing to full No rvil pro­du ction racing standard s . If required , cylinder head s will he gas -flow ed and bor ed to accep t 32mm Ama l Con centri c ca rbur e llor s and crank shaft s balan ced.

DUCKHAMS PRODUCTS BRIGHTLY colour ed blu e, ye llow and white display ca rton s a rc now b eing u sed to pack an in creasing number of Du ck­h ams pr odu cts. The lat est to be includ ed a_rc Un iversa l Brake F luid, 26 ,}p per 8oz tm; :iiou sehold Lubri ca ti ng Oil , lOp p er 5oz tm; Kccno l Grease llp per 4oz tub e and Pa lmit Hand Cleanser, llp per 4oz tub e.

We append de tail s of some of th ese produ cts lik ely to be of p articular int eres t to rea ders : Kc enol Gr ease is a lithium b ase multi-purpo se grease whi ch include s a special add iti ve or igin ated by Duckham s b ase d up on zinc ox ide wh ich imp art s exte nsive wear-res ist in g and stay-p ut prop erti es . It is s ui tab le for all genera l greas ing. I t is particularly r ecommended for any component wh ich ca n only be grease lubri cate d at infr equent int ervals such as brake operatin"' mechan isms clutch spi got races. (I t i; ideal for mo s~ boat ing ap plication s in clud in g ste rn glands, prop ell er shaft bear ings , rig ging screws, etc .)

Evaluation of a £330 h.o. twin with clear BMW antecedents

Russia's 650 Ural M63 WH_EN a "new" countr y ent er s th e

motor cycle sce n e it is natural th at ther e should be a numb er of qu es tion s about its produ cts. \Vh cn it offer s machin es a t h alf th e pri ce of it s ri va ls, the se qu es tion s tak e on greater sig­nifica nce. Th e potential buy er is goin g to want to know i f corner s h ave be en cu t to produce a t su ch a co mp etitive pri ce. H e is going to w an t to kn ow if spare s will be availabl e , how mu ch th ey will cost and who will he abl e to do rep airs for him . He is al so going to ask how good is th e ma chin e . In th e case of th e Ural , rid er s are also go in g to ask if it s r ese mblan ce to the older BMW s is more th an skin dee p. Th e ma chin e p oses enough que stion s for a write r to k ee p going all ni ght. Some we h ave answered , we think, abo ut oth ers we are not so sure. Fir st, le t u s loo k at what is per­hap s th e mo st intri guin g point of all. The Ural' s un canny r esem bl ance to th e BMW. Coinciden ce ? Far from it.

Little is known of the Ru ssia n motor­cycle indu str y but it i s not unr easonable

10 think , con cerning the ma chin es now ava ilabl e in Britain , th at, la cking th e ex peri ence to desig n qui ckl y "s tr aight

r

off th e bo ard " , the y examin ed the estab ­li shed produ cts of other nations and decided to make repli cas of the be st of th em. From t11e design used here we would say that the period in ques tion was the ea rl y 1950s. The Ru ssians did n ot confin e th eir effort s to the flat-twin co ncept , thou gh, for curr ently on view in thi s country are a 50 c.c . mop ed that ju st has to be a close r elative of the NSU Qui ckl y, a 125 copy of the Bantam (whi ch was a copy of the DKW - tak e your pi ck whi ch on e the Ru ssia ns used), and 175 and 350 d erivation s of old er ] awa / CZs.

Let us look a littl e mor e closely at the ancestry of the Ural. It do esn' t need mu ch im agination to place it as a close relat ive of the pre-E arl es .fork BMW ; but to look to th e R67 for help is not the an swer-not in the engine ro om at least. It goes back furth er than that. Right ba ck to the 1930s when BMW mad e the mod el R66, whi ch wns a 600 c.c . over­he ad-valve . Our research has shown the Ural engine to he very close ind eed in constru cti on to th e R66 . Unfortunately we were unabl e to find an engin e drawing of th e R66 in the time availabl e but we

'

have reprodu ced here drnwin gs of the R71, a 750 side-valv e ver sion of the same marque.•

Stu dy the two engine drawing s and not e tl1e similaritie s. Crankcases are identi cal except that the front timin g cover on the Ural i s cut sh ort , a lo gical step for it was wasted spa ce on the R66 . Note how the sump cover s h ave th e same kink in the left-hand side to clear th e oil pump. N ote, al so, how both oil pump s pass through the left side of the crank case, appearing at tl1e top b y the dynamo. Bot11 are identical in con­stru ction , both use the same lar ge nut for fixing to the top of the crankca se. The oil pump is in a separate drawing for the Ural and in pl ace on th e BMW . Note how the rear main bearing and hou sing are removable from the rea r of the en gine on both ma chines. Th e R66 was one of the las t BMW s to use thi s

*Bear with us, reader, when you look for th ese drawings-and don't find th em. Lack of space, pre ssing printing schedule s, thi s excuse, th at . . . ha ve meant that we hav e been unabl e to print them. So ple ase accept our word for it when we detail the similarities. E d.

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Moto rcycle S port , Jrm e 1971 2 13