THE CLASSIC, COMPLEX CR93 · d · racer Analysis and track test of Honda's 125 dohc twin pro ucuon

THE Honda CR93 125 c.c. Produ ction Ra cer was perhap s th e ni ces t rac er

ev er offered for sale to th e publi c . 1Vter nea rly a de ca de th e droning dohc twin s still make the leaderboard a t th e TT, yet never figure w ell in th e spee d trap hi e rar chy. The 125 twin i s of classic de sign with gear-driven doubl e-overh ead ca m shaft s and four valves in ea ch cylin­der. The whol e machine is of such a small size th at th e overworked metaphor o f "wa tch lik e" pr ec is ion is ju stified. Thoug h outclassed b y th e two -strok es n ow , the l on g lon g ra ces on the I sle of Man still allow th e magnifi cent r eliability of thi s cla ss ic motor to win thr ough.

A small bat ch of CR93 s was produ ced with full r oa d equipm ent , and th ese few ma chin es are n ow to be found in the · private co ll ec tion s of rich and enthu si­asti c Americans. T here are a few ma chine s that m erit th e descripti on " cla ssi c" eve n though th ey ar e still active on the tra ck s toda y. The li st is short but th e entrie s ar e familiar. The Manx No rton s, the Match less G50 and AJ S 7R, the MZ 204, th e Honda CR9 3 head thi s li st and w e intend to obt a in tra ck impr ession s of eac h and all of th em , treatin g them as modern ra cin g ma chin es

-16

374 Mo torcycl e .Sport ,. Octol}er 1972

and makin g n o allowan ces for th eir elderly design and con stru cti on. One severe problem is that of loca tin g such ma chine s in original conditi on. l have been looking for a Vin cent Shadow in original spe cifica tion and goo d eno ugh cond ition to rid e fairl y qui ckl y for severa l years-wi th a compl ete l uck of success . All th e " original " machin es th at one loca tes swiftly di splay feet of cla y as one modifi ca tion after another emerge s und er th e str ess of verbal examinatio n. Mu ch the same situation exists for these old rac in g machin es, and th e numb er of original- spe cificati on bik es is seve rely limited.

The first of th ese ma chin es to beco me avai lab le was the Honda CR93 owned b.y Tom Lou ghrid ge. The offer to tr y it aro se at a chan ce mee ting at th e Spon don Enginerin g stand at the Show at th e Ho.r­ti cultural Hall s earlier thi s yea r. Late 111

April we met at Silver stone durin g a Southern Sixty Seven Racing Club prac­tice day , and a fair fleet of two -stro ~es pour ed out of Tom 's van , together with the lit1le Honda .

Althou gh it is a 125, the machin e as a whol e is fairl y b ig. It is certainl y heavy for a 125, and is lon g enou gh for men as

lar j:!e as Tom and ' '.ty~clf lo fit on Lo it in c:omf orl. Co mfort b no luxur y on a lon g nwe. T he 111cr cs 1 ar he in an ankl e or wri st .. an be1"om c cripplin g aft er the first h our or so.

Th e hi :.d1, w_id c anti hand some riding posit ion naturally mean~ that the CR93 is hardl y th e small e, 1 of 125s. In fal"t it mu st b e one of th e bi gges t, and certainl y th ere ca n l,c few heavier ! A dry weight if 128k g (3101b to the unm c lric ated ) is suh stunliall y in ex ,·c,, of th at of a TD2 250 Ya maha. W h erea s th e Yam aha ha· 250 c.c. and about .i.1 l,.h .p . a l 10,000 r.p.m ., th e " Jilli e" Hon<la hns around 10 .5 b.h .p. at 11,500 ( a figur e tha t C see in th e manual and hcg leav e lo do ubt a fter riding th e m:whin e , as e\"en th e H onda UK data shee t refer s Lo gea rin g for 13,500). ·aturall y th e Honda is no ball of fire in acce le ratio n : how e\"er. thi s do es not mean that th e top speed is low.

Af ter a long run -in ove r 100 111.p.h. is availabl e, and ce rt a inl y it mu , t be easier lo maint a in suc h a l on µ:-lcµ:ged pa ce on th e I sle of Man clue to th e smoo th pow er de liv ery and reasonable pow er band. T his is very mu ch Tom Lo u;.:hrid ge· 5 cx ­perien,· c : neve r d oe s hi s CR93 show up in th e first f cw ( or even th e fir; t 10}

125 c .c . s p ee d t rap fig ur e ,;, but n eve r th e­less h e ge ts on to th e lcad c rhoard within a lap. The oth e r v irtu es r eq uir ed of a heavy 125 a r e good brak es and goo d handlin g. The Honda 1·e rt ;1inly ha s th e brake s- whi ch work ex tr c m e h- well - but tJ1e h andlin g und e r 1, le of Man ,·o nditi on s is no t so goo d. A t S ilv er s to n e . h oweve r. the CR 93 handl e s well and aho stee r s beautifull y. Th e sm oo th s urf:u· e of the airfi e ld c ir cuit do c s n o t r e all y provoke tr an ge ant ics , and th e s h ee r w e ight o f

the m ac hin e te nd s to h e lp a bit in th e i land. Th e n ee d to pr e;,,; 0 11 a h it plu s the lol\I r oad s i s th e co mbinati on th at pr ovo ke s co mpl ain t.

W h e n con s id e ring lonµ:. 10 11µ: ra.- es su, ·h as the ; c, th e sh ee r reliability of th e Hond a is a c on s id e rable a sse t. La s t ye ar thi s wa s p r oved t o b e tru e, but s in ce thi s articl e wa s fir s t draf ted Tom Loughridge has run in th e 1972 TT wh e re h e wa s for, -ed to r e tir e af te r abou t a lap wit h en gin e. po ss ibl y cra nk sh aft t roub les . The o ri gin s of th e C R93 w er e in th e flee t C B92 road ma chi ne. Thi s shar pl y styled liul e 125 wa s prov ed to b e capabl e of over 80 m.p .h . on th e road a d ecad e ago. It i s worth rcmemhe1·inµ: that , wh en ful some pra ise is b e in g b e ;.t owe d o n 80 rn.p .h . 125 s of tod uy : th a t old Honrla rea ll y h a<l s peed. Th e C B9 2 wa s- and still i s- th e ba s is for qui te a few ra cin g 125s, p ri va tel y co nv ert e d b y u s in g Honda Race Kit s. Con trar y to pr ese nt day po li­cies. o n ce u po n a tim e in th e Golclcn

Day s Hond a (U K) used lo bring in Ra ce Kit s . Sadly the se day s are lon g past, and you ca n beg in va in for eve n a knobbl y rnm sh aft for your Produ ction Ra cer these day s . . . unl ess yo u go to Fr ance : or Swed en : or USA: or Singap ore : or . • . .

Th e CR93 w as never a converted road m ac h ine. It was, ind eed, ba sed on the C B92, but ra c in g developm ent was ca rri ed out by Honda (Japan ) an d a sur­pri sin g nu mber of CR93 s wer e produ ced­eve n a few in full road trim, with li ght s, stan d s and oth er ro ad legal fitm ent s.

T he bar e tec hni cal detail s of the CR93 are ns foll ows : len gth, 2 metre s ; width, 0 .6 me tr es; h eight , 0 .9 metr es ; whe elba se, 1.3 metre s ; ground cl earan ce, 0.15 me tr es ; dry weight 128kg, bor e 43mm, strok e -l3m111, di spla cement 124.8 c.c.; comp ression ratio, 10.2: 1; carburettor s K e ihin RO:,!\I, 22P6; fuel capacit y, 10) litr es ; oil ~,imp, 1.1 litr es ; clut ch, dry multipl ate ; tr an smi ssion , five gears : 1st, 1 : 2; 2nd, 1429; 3rd 1 : 227; 4th I : 083; 5th 1: 01 tyre s-2.5 0 x 18in front , 2.75 x 18; igniti on-e nergy tran sfer.

T he pr eparation s for running the CR9 3 are spelt ou t with great cure in a data ;.hee l pr epar ed by Alf Brigg s nt Honda ( UK ). Alf hus for many years kept tJ1e CR9 3 and CH.llO rac ers on the tra ck by hi s valiant effort s in obtaining and issuin g spar es from a sto ck that is kep t with (but not of) , the res t of Hond a's cent ral stork s in the UK. T hi s servi ce is not ju st

extended to tho se rid ers in the UK : hi s customers are worldwid e . Surpri singly, after so many years there are still enoug h genuin e spar es to ke ep several CR3 s run­nin g, and running weJI . Honda did in­de ed produ ce one of their ex cell ent spar es li sts for the machin e, and with typica l thoroughne ss even megaphone caps and ma chine stand s have th eir . own i llu stra­tion and part numbers. The dat a sheet tak es up wher e the factor y left off, and embodi es mu ch of the experience gained by rid ers runnin g CR9 3s in th e UK. Remember Rod Scyvie r 's Briti sh Cham­pion ship on a CR93?

Warmin g up tl1e CR93 i s don e on soft plu gs and i s a fairl y slo w proce ss : the howl from the megaphone i s a delightful change from tl.1e two- strok e, and s.ee.ms po sitively mellow af ter the head-sphtt~ng screa m of ma ssed two -stroke s, to win ch we lrnve become painfull y accustomed in re cent years. (Sure ly ,some cleve r engi­neer could find a way of ge t tin g all that wasted ener"y into the en gin e and onto

" . . ?) the back whe el-and give qui et aga m. On ce the en"ine i s warmed, the oil i s

" · NG K chan ged and hard plu gs put m . C9H (warm ) and 13/ 14H (hot ) u sed to be suggested. In addition to thi s pro cess , it is recommend ed that th e oil be war~ ed befor e starting the ma chin e up .. Like mo st Hond as , the CR93 ha s a centrifu gal oil filter and thi s mu st b e cl ea ned out each .tim e the oil is ch ange d . Th e. R20

. grade is u sual , wiili R 30 for hott er limes.

FRONT BRAKE ASSEMBLY

12

IGNITION

lb

13

~--@ ' IZ 13 12 ®--@ ,~ '

12 IJllP1 IZ 13

Motorcycle Sport , October 1972 375

A compact and elegant device that does its job superbly

The standard CR93 change ha s been altered on Loughridge 's machine lo give the UK lef thand braking / righthand gear. change, in oppo sition to standard Japane se practice. The rear suspension unit s are now Girling s rather than the (unadju s tab le ) Japane se units originally fitted. I got aboa rd after a briefing on r.p.m . limit s and ge ar change pattern , and painfully puJled away in fir st gear. The gearchange wa s rea sonably light , and had a short enou gh throw to sati sfy my per­sonal des ir es in that direction . Th e clut ch is dry - fortunat ely, as one mu st slip it fairly severely to get off the mark. On ce one wa s moving , the engin e wa s quite pr epared to try to pnll you along at low r.p .m., but reall y anything below 7,500 was a wa ste of tim e, as it took so long to build back up again to the power band. As the rev s . rose there wa s no rea lly sharp pow er delivery change, it just seemed to pi ck up and smoothl y acceler­ate away as 8-9,000 was reached. The engin e is said to deliver fuJl pow er at 11,500, but I was asked to keep it "down to 12", whi ch seems rather at variance with thi s. The power wa s sh owing no

sign s of tai lin g off mu ch at th at figur e, and ind ee d that data sheet mentioned earli er recommends a red line of 13,500-and adds that 14,500 is the ab solute limit and "this will prov e expen sive if often u sed". I don't doubt it. The brake s were deli ghtful : the twin-sid ed, four- sho e la y­out i s th e original "wor k s" pattern and i s sin gularly effective. The bit e is 'a bit sudd en, and th eir power is such that after braking for Becketts Hairpin on the fir st o ccas ion it proved ne cess ary to accelerate again before rea ching the corner it sel£; Down the straight, or should one say " up" at Silverstone?-th e s tr aight is actually uphill for most of it s le n gt h- th e CR93 tr avelled rapidly and smoothly. The bulky fairing and long

376 Motorcycle Sport , October 1972

riding position made it po ssible for me to get well tu cked in , and th e contro ls all fell to hand wi thout any contortion s : it is obviou s that Tom Lou ghrid ge ha s se t th e Honda up to fit him as he is a little large r tlian I am, and ' ce rtainl y bigg er than mo st 125 rider s.

Handling thr oug h the fast Wood co tc corner was r eassuring, but there was some hint of pit ching. The no rmal fork oil is 170 c.c. of SAE5 Shocko l ( Castrol ), but I am not sure what was in th e fork s on thi s occasion . Perhaps it cou ld hav e bee n a bit harder with advantage. The " ride" was comfort able too , so it is probabl e that both fr ont and r ear were set up softly. Like any small capacity ra cing machin e c:ir was necess ary to keep th e engine on the power band , but th e sheer pun ch th at the 125 Yamaba s now deliver was quite ab sent. Thi s gene ral lack of power b y pr esent standard s wa s demon strated by th e lap tim es of around lm 29s-32s for the Honda compared with th e low 20s for the Sondel Yamaha und er similar condition s. It is likely that the full use of the avai lable rev. range would ha ve cut a bit off the Honda' s tim es, hut th e

FRAME

Sondel Yam was not used to i ts r ev. limits ei ther. There was no doubt in my mind which ma chin e I would rath er ride for a very long ra ce . The CR93 rem ains one of th e r are ma chin es; the me ch anica l elegance of thi s small pre cision j ewel is very appealing. The cost of necessary spare s is th erefo re far from as desirable, for ju st the same rea son s.

A great deal of carefu l preci sion work is needed to set up a CR93 correc tly. The tappe t adju stment is carri ed out by stoning the cam follow ers "absolutely square ", to quote the sheet of word s, and if th e tappet clearan ce is excessive th e contact face mu st ei ther be built up with hard facing weld or the tappets replaced. Th e clearance s are 6 thou with a toleran ce

of on ly plu s or 111inu5 ). ;; thou, so thi s. show s th e ca re r equir ed . The pi ston rin~ gap is a minim um of .i th ou , and th e pi ston cleararw c should n ot exceed 0.lmnL at th e thru st fa,· £'. Surpri s ingly th ere arc thre e rin gs on th e pi ,-ton . Th e valv e gear and th e doul,le ov erhe ad camshaft head ar e th e central fca111re:< of the ma chin e. Drive is tak en tu th e ,·am,-h afts b y a train of gear s, and ii is th er efor e n ecessa ry to adju st fr ee ,·lcara n.-e~ by u,-in g a range of diff ere nt thil'kne:- :<e~ of head gas ket: mor e tim e, ca r e , and ,·h e,·k in g for pre­paration.

A ba ckla "h of 0.6111111 111u, 1 h e provid ed for 1he .-am~haft dri ve gea rs . Th e four va lves per cylind e r layout a ll ows good breathing , but ce rtainl y multipli es th e lim e r eq~ir ecl to get a ll ,ct up ,·orr e ,·tlv by a notable faet o r. Va lv e spring s mu ; t be r epla ce d if th e fr ee len/! lh ha s dropp ed b elow 32A mm (out e r ) an d 28mm ( inn er) . Four valv es p er r-yli nder. two cylin der s, and tw o valv e spri ng s per valv e indi ca tes a lot of work is n ee d ed . Th e valv es th em­se lve s sh ould h e .. han ge d a fte r eith er a season or a TT. Igniti on is dir ec tl y via th e genera tor , an1l th e u,-ual cam shaf t­driv en pair o f point s ar e pl atinum faced. Hea d tight ening torqu e i~ l 4-16lb / ft . It i s int er esting to not e tlrnt an automatic advance / re tard unit is fitt e d to thi s ra ci n g ma chin e. T he carbur ettor s tak e a range of main je sls, ancl 80, 82. 85, 88, 90 ar e the li st of Ho nd a sp ecifi e d se ttin gs. A very narrow rnni:re, and inde ed Hond a rid er s ha ve b ee n known lo ge t int e rn1e­diatc va lu e ma1le up f or eve n fin er mixture control. P il ot jet setting: is 40, and th e float he ight 2:3111111. T he latt er is m easu r ed wit h inv ert ed ,·arbur e ttor v ia th e d is tan ce b e tween top of 1he float and th e float bowl se tting .

The whole of th e e n1?inc is li1t er ed with nee dl e roll er s and ball '(\lies for every con ce ivable b e arinJ!. Th e cam shaft s run in hall ra ces, th e camdriv e gea r s run on ra ces, th e crank main s and big end s arc roller bearing s, th e gearbox run s on roll er bea ring s throughout. An intere s ting ommision is th e clu1ch, whi ch doe s NOT have a hall ra,. e for th e dut ch throwout plate!

Th e fr am e i~ a hea vy ~pine with th e en gine u sed as th e l ower m e mb er , unli ke the CB92's pre sse d fr am e.

Th e CR93 ha s mu ch in common w ith th e Honda Ju.no , in that it is a co 111plex, compa ct and ele gant de vice that doe s it s design ed job superbly at th e expen se of requiring ex pert and considerate tr ea t­m ent. A rea l classic of the tra ck , and if onl y Japane se labour costs were low e r we could hope to see CR ver si ons of the m or e re cent mach ine s with a similar degr ee of refinement. Unfortunat ely tho se days see m to ha ve go n e, and th e sp ec ial conditions that allowed Honda to co n si· der the produ ction of th e four- stroke Pro• du ction Ra cer s of thi s degree of r efin e­ment ha ve now gone . We mu s t co ntent our selve s with nostalgic loo ks. Our grat e· ful thanks to Tom Loughrid ge for pro· viding u s with th e opportunity. M.R.W.