JCM

The JCM tri­als ma­chines were the re­sult of the ef­forts of their vi­sion­ary cre­ator Jöel Cor­roy, who is still ac­tive in tri­als and runs the very suc­cess­ful Trail 70 con­cern to­gether with many tri­als in east­ern France. The star burned bright for a few glo­rio

Classic Trial - - FRONT PAGE - Words: Matthew Hep­ple­ston Pic­tures: Hans Greiner and Matt

Ihave known Jöel Cor­roy for a num­ber of years and to­day he is still as pas­sion­ate about the sport of mo­tor­cy­cle tri­als as he ever was. His shop, named Trail 70, in Ve­soul, is a multi-fran­chise deal­er­ship sell­ing all man­ner of ma­chines. Up­stairs there is an ex­cel­lent mu­seum cov­er­ing off-road ma­chines and a sec­tion ded­i­cated to JCM which in­cludes some pro­to­types and pro­duc­tion moulds. If you look at pe­riod pho­tos of Mick An­drews you will of­ten see the shop’s name dis­played on his rid­ing gear.

Dur­ing the 1970s and 80s Trail 70 be­came the ref­er­ence point for the de­vel­op­ment and im­prove­ment of many Span­ish mar­ques, par­tic­u­larly the Ossa. With this wealth of ex­pe­ri­ence he de­cided to take de­vel­op­ment work to its ul­ti­mate and log­i­cal con­clu­sion and cre­ate his own ma­chine. The first pro­to­type was built by 1st March 1982 and was the first mod­ern tri­als ma­chine to be pro­duced with a monoshock for the rear sus­pen­sion.

JCM

The JCM Com­pany was cre­ated at the be­gin­ning of 1983 and, along with Charles Coutard, con­ceived a very compact frame with an ad­vanced sin­gle shock, us­ing an air-spring rear sus­pen­sion unit. The pow­er­ful mo­tor came from the Ital­ian Tau fac­tory. The pro­to­type was very suc­cess­ful and pro­duc­tion ma­chines were be­ing pro­duced by Novem­ber. An ex­cel­lent public­ity ex­er­cise on the 26th Oc­to­ber had Charles Coutard and Joel Des­cuns rid­ing up and down the two first lev­els of the Eif­fel Tower! If you have ever walked up it you will know how tight the turns are, up the never-end­ing stair­cases.

The model we tested is ac­tu­ally a 1984 model. In to­tal some 420 ex­am­ples of this sec­ond gen­er­a­tion JCM were made in 1984 and 85. Th­ese were the pro­duc­tion version of the mod­els rid­den by Charles and Joel. The JCM has al­ways been a very in­no­va­tive ma­chine and they in­tro­duced the first monoshock tri­als ma­chine, which was pow­ered by the Tau en­gine mounted in a fab­ri­cated steel frame. The footrests fea­tured a sub­stan­tial bolt-on mount­ing plate which en­abled easy re­place­ment. Fuel was held in the con­ven­tional po­si­tion un­der the tank cover. There is also a strong wide, flat sump plate act­ing as a stressed frame mem­ber. Forks are the in­dus­try stan­dard Marzocchi mag­ne­sium slider units fit­ted to many other ma­chines of the time.

The Tau en­gine is dif­fer­ent in the way the crankcases split hor­i­zon­tally — like to­day’s Ver­tigo — rather than by the more com­mon ver­ti­cal ar­range­ment. It is a con­ven­tional pis­ton ported two-stroke. It is well over-square with an

82mm chrome plated bore com­bined with a 60mm stroke. The ca­pac­ity is 317cc and the claimed power out­put is 19bhp @ 6000rpm. It has a sixspeed gear­box fit­ted. The clutch has a bolt-on al­loy ac­tu­at­ing mech­a­nism op­er­ated by a me­chan­i­cal lever. which also serves as the mount­ing point for the chain de­rail­ment pro­tec­tion. It would have been easy to up­grade to a hy­draulic unit at a later stage if re­quired.

The pro­duc­tion model fea­tured an air in­take un­der the steer­ing head bracing; air was then drawn down through the top frame tube into a large-vol­ume air­box, where it passed through a Twin air fil­ter into the car­bu­ret­tor. Main­te­nance ac­cess for the fil­ter was through a large cir­cu­lar hatch on the left side. This raises the air in­take to the high­est point on the ma­chine away from mud and wa­ter.

Hand Built

It is clear, look­ing round the mo­tor­cy­cle, that a lot of thought has gone into the de­sign of the hand built ma­chine. High qual­ity com­po­nents abound and the lines are smooth. The ex­haust is well tucked in un­til the rear si­lencer, which may be a can­di­date for re­place­ment in a mega crash as the fix­ing does not look very sub­stan­tial. The fuel tank / seat unit is held on by a front bolt and a clip at the rear, mean­ing it can be re­moved in a few sec­onds. The rear sub-frame can then be un­bolted, the si­lencer and air fil­ter con­nec­tion loos­ened and the en­tire rear end re­moved as a sin­gle com­po­nent. This means ac­cess for main­te­nance is un-par­al­leled.

The rear sus­pen­sion is prob­a­bly the most ad­vanced fea­ture that is di­rectly mounted to the box sec­tion swing arm. The sus­pen­sion unit, which is of a JCM patented de­sign, does not have a spring but in­stead uses Boyle’s Law to pro­vide pro­gres­sive com­pres­sion and ex­ten­sion of the sus­pen­sion. There are, how­ever, lim­i­ta­tions to the sys­tem such as the high ini­tial force re­quired to over­come the large seal sur­face re­tain­ing the damp­ing oil, which is sep­a­rated from the pres­surised air cham­ber by a blad­der and the ab­so­lute reliance of the flex­i­ble rub­ber blad­der to main­tain gas pres­sure. In ad­di­tion the gas tem­per­a­ture also needs to be con­stant or the damper char­ac­ter­is­tics change more dra­mat­i­cally than in a con­ven­tional sprung unit. The use of a large alu­minium body, which acts as a ra­di­a­tor, min­imises this ef­fect.

In the UK the ma­chines were im­ported by Quinn’s of Gateshead and rid­den by riders such as John Reynolds and Phil Alder­son. The test ma­chine was sup­plied by Joel and had been lov­ingly re­stored in his work­shops back to fac­tory fresh con­di­tion. Our good friends from

First Im­pres­sions

The first thing you no­tice is that the short, high-mounted kick-start re­quires a fair ef­fort to turn over the 317cc en­gine with an 8.5:1 com­pres­sion ra­tio. The en­gine can be started with a gear en­gaged, and it starts im­me­di­ately thanks to the elec­tronic ig­ni­tion that is fit­ted. The en­gine note is well si­lenced with a char­ac­ter­is­tic metal­lic rat­tle from the steel mid­dle-box and si­lencer. The revs rise and fall quite slowly and the in­er­tia seems high, as it takes a while for the revs to die away when blip­ping the throt­tle. The clutch has a nice light feel and first gear en­gages with a gen­tle clunk. Mov­ing off, the first thing you no­tice is that the front end of the ma­chine feels quite low and the forks are very softly sprung. In con­trast the rear unit feels much stiffer and much more re­ac­tive; just like a mod­ern tri­als ma­chine in fact. The rear wheel travel seems much more sub­stan­tial than a twin-shock. The claimed travel is 8.5 inches, which is about two inches more than nor­mal, and it cer­tainly felt more ‘plush’. It also has more of a marked pro­gres­sive feel to­wards the end of its travel, ex­actly what you want!

One thing that is to­tally dif­fer­ent is how light the front end of the ma­chine is. Even a gen­tle open­ing of the throt­tle lofts the front wheel and makes floater turns so sim­ple if you have the skills. Per­son­ally I found it more than a lit­tle dis­con­cert­ing to be climb­ing and turn­ing on a bank­ing and sud­denly all front tyre grip dis­ap­pears! A swift dab was the in­evitable re­sult for me. Hans how­ever, be­ing in a dif­fer­ent class, showed how you could flip the front end round us­ing his body English style. The steer­ing head an­gle feels mod­ern in that it is so re­spon­sive, and tight turns are easy on the level.

Weight dis­tri­bu­tion is bi­ased to­wards the rear. I found the re­la­tion­ship be­tween footrest and han­dle­bars to be very good, un­like a Yamaha TY mono-shock where the footrests feel high al­though the front end seems low; a set of higher han­dle­bars should cure this sen­sa­tion.

Tractable Power

The en­gine it­self is a corker; pow­er­ful, strong and yet smooth as you can let the revs drop right away and, only us­ing a whiff of throt­tle, search for grip with the help of the ul­tra- com­pli­ant rear sus­pen­sion, or wind it up with the clutch slip­ping and then drop the clutch and burn through to a solid sur­face be­low. The only ob­sta­cle to this tech­nique is the light front wheel, and you really need to get your body in po­si­tion be­fore let­ting fly. Per­son­ally I liked the tractable na­ture of the pi­lot jet but I was cer­tainly aware that there was a lot of po­ten­tial wait­ing to es­cape if I was not care­ful in tight cor­ners or del­i­cate sit­u­a­tions.

I found steps the most daunt­ing as­pect as you needed some speed to climb them rather than be­ing able to blip the throt­tle at the base. Ba­si­cally you need to plan ahead and ex­e­cute per­fectly, which is not my forte I con­fess, but watch­ing Hans you re­alise the ma­chine has lots of po­ten­tial in the right hands. I did not enjoy rid­ing down­hill so much, as the low front end com­bined with the softly sprung forks and frankly less than in­spir­ing Leleu front brake gave the im­pres­sion that things could quickly get out of con­trol as the steer­ing be­came very re­spon­sive in th­ese cir­cum­stances. I would have pre­ferred a much stiffer set of springs in the front or per­haps slightly less pres­sure in the rear unit to level the ma­chine up more. Joel later con­firmed that the rear sus­pen­sion was slightly over pres­sure. I am will­ing to give this is­sue the ben­e­fit of the doubt if we could have had more time to set up the rear shock. Hap­pily the back brake pedal was per­fectly placed and the rear drum brake worked well! You cer­tainly need to get your weight a long way back for con­fi­dence.

So, how could you best sum up the ex­pe­ri­ence? The ma­chine it­self would have been at the peak of per­for­mance for the time, if you watch video clips of riders of the time such as Charles or Bernie Schreiber on the SWM Jumbo they climb all over the ma­chine as they ne­go­ti­ate a sec­tion. Watch­ing a good rider like Hans, who also rides a Bul­taco Sherpa in clas­sic events, ride in a sim­i­lar style makes it ob­vi­ous that you need to be much more phys­i­cal and dom­i­nant than on a mod­ern ma­chine. I guess my near­est de­scrip­tion of an­other ma­chine to com­pare it with would be a late model Bul­taco Sherpa with a rear sus­pen­sion that really works.

So there you have it; a ma­chine that her­alded the dawn of a new tech­nol­ogy com­bined with the rid­ing sen­sa­tion of a well tried and tested for­mula should have re­sulted in much greater suc­cess for the mar­que. Un­for­tu­nately the Ja­panese Yamaha fac­tory were to pro­duce the equally ground break­ing TY250 mono and, given the re­spec­tive re­sources avail­able for de­vel­op­ment and pro­duc­tion, there was only go­ing to be one win­ner. The JCM star burned very bright from the be­gin­ning and then faded as the com­plex­ity of com­mer­cial­i­sa­tion and se­cur­ing the nec­es­sary funds to grow the busi­ness be­came ap­par­ent. I won­der if there is a les­son to be learnt to­day.

Our thanks go to the ever en­thu­si­as­tic Joel for the prepa­ra­tion and loan of the ma­chine and to Hans Greiner for shar­ing the test with Clas­sic Trial Mag­a­zine.

Note: “Boyle’s law is a gas law which states that the pres­sure and vol­ume of a gas have an in­verse re­la­tion­ship, when tem­per­a­ture is held con­stant. If vol­ume in­creases, then pres­sure de­creases and vice versa. When the vol­ume is halved, the pres­sure is dou­bled. It can be math­e­mat­i­cally ex­pressed as: Pa”

In­no­va­tion could be found every­where, like th­ese in­board chain ad­justers

The sus­pen­sion is put to the test by Hans Tri­al­sport in Ger­many were also present in the form of Ed­i­tor Hans Greiner, who is a for­mer top-20 World run­ner, and the re­sults are a com­bi­na­tion of our im­pres­sions.

We were rid­ing a few hun­dred yards away from the vil­lage of Ar­be­cey, which is the home of Joel and the su­perb two-day clas­sic trial so we were sure the JCM would cope with the ter­rain as I sus­pect a lot of de­vel­op­ment work was done in the sur­round­ings.

The large mo­tor was a snug fit in the frame and ac­cess for main­te­nance was very good

The rear si­lencer was very ex­posed

Hans uses ‘Body English’ to hold the line

It was quite ‘busy’ around the car­bu­ret­tor area

Joel Cor­roy with his JCM col­lec­tion in his own mu­seum

Matt turns on the style for the cam­era

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