Trifield

Fash­ions change and times move on, and Pre-65 ma­chines are no ex­cep­tion. In the early days the Sammy Miller Ariel 500cc replica was the ‘bees knees’, and this trend evolved through the lighter ma­chines such as the four-stroke BSA C15/B40 and Tiger Cub, th

Classic Trial - - CONTENTS - Words: Matt Hep­ple­ston • Pic­tures: Matt and Steve Martin

Choos­ing your Pre-65 mount is a del­i­cate choice, as there are so many op­tions to cre­ate a highly com­pet­i­tive ma­chine us­ing the myr­iad af­ter­mar­ket parts that are avail­able. Once you have de­cided on the for­mat: four-stroke, two-stroke, large or small ca­pac­ity en­gine, sin­gle or twin cylin­der, then the fun be­gins in cre­at­ing your ideal ride. If you han­ker af­ter a twin-cylin­der en­gine then the choice seems to be quite lim­ited.

A Tri­umph Twin is by far the most pop­u­lar choice, although I have rid­den an Ariel Ar­row and the Le­je­une Honda twins. The Tri­umph has been pop­u­larised in re­cent years by Steve Saun­ders, who used one to win the 2011 Scot­tish Pre-65 event, fol­lowed up by Rob Bowyer in 2014. Although if you look back through tri­als his­tory there were not many rid­ers of the time, with the ex­cep­tion of Johnny Giles and Roy Pe­plow, who ever won ma­jor

events on these ma­chines. So what has changed in the for­tunes of the Tri­umph Twin? For most, I guess, the path starts when they hear one in ac­tion. The rorty, rasp­ing sound of the twin on full song is un­like most other you are likely to ex­pe­ri­ence at a Pre-65 trial. This is the ma­jor rea­son owner Mark Stokes chose to build the test ma­chine. He also wanted one that was el­i­gi­ble to ride in the Scot­tish Pre-65 event, and rode to a Spe­cial First Class award in 2014. So I was sure the test ma­chine was fully sorted.

Royal En­field Chas­sis

This ma­chine, like Steve Saun­ders’ ver­sion, has the en­gine built into a Royal En­field Cru­sader frame which, un­like the Tri­umph ver­sion, is all welded as op­posed to the ‘lugged’ orig­i­nal and gives a sig­nif­i­cant ad­van­tage in terms of weight and more im­por­tantly wheel­base, as the swing­ing arm can be tucked much closer to the rear of the crankcases than on the Tri­umph, whose mount­ing point is a large cast lug be­hind the gear­box. The wheel­base is cur­rently 52½ inches, which is sim­i­lar to a mod­ern ma­chine, and very rea­son­able nev­er­the­less.

Mark poured over many pho­tos of the Sanders ma­chine and fit­ted the en­gine in ex­actly the same place. This ne­ces­si­tated cut­ting the swing arm mount­ing brack­ets and re-weld­ing them in such a po­si­tion that when the rear sus­pen­sion travel is half used there is a straight line be­tween the gear­box out­put sprocket, the swing arm mount­ing point and the rear wheel spin­dle. Cus­tom al­loy plates lo­cate the front of the en­gine and a sub­stan­tial head steady con­nects to the top frame tube.

Once the en­gine is fixed then the an­cil­lary parts need fit­ting or fab­ri­cat­ing from scratch. Start­ing at the front end a set of al­loy yokes from a well known in­ter­net auc­tion site was fit­ted. These mount the han­dle­bars slightly in front of the steer­ing step and are fit­ted with Ren­thal han­dle­bars and Domino levers, and a fast-ac­tion throt­tle. The forks are Royal En­field low­ers with a slight lead­ing axle and the in­ter­nals are by Be­tor from an Ossa Grip­per. To en­sure Scot­tish el­i­gi­bil­ity the wheels are fit­ted with replica Tiger Cub hubs sup­plied by Alan Whit­ton Race En­gi­neer­ing, laced with stain­less spokes to a black SMPro Plat­inum rim, which I think adds a classy mod­ern twist to the look! Rear sus­pen­sion is taken care of by some cus­tom-built black an­odised and sub­tly en­graved Rock­shocks sus­pen­sion units. The petrol and oil tanks are cus­tom built, and they hold suf­fi­cient fuel and oil for most events. As Tri­umphs are renowned for run­ning hot, a trick oil cooler from a Honda XR400 model tucks neatly around the steer­ing stem, feed­ing cooler

oil to the rock­ers. The ex­hausts are high level, made by Dave Tyler, and are ce­ramic coated in­side and out to re­duce the tem­per­a­ture. They exit into a tiny al­loy si­lencer just un­der the seat, which was fab­ri­cated by Chris at Sil­ver­back En­gi­neer­ing. Sur­pris­ingly for such a small item the ma­chine is ac­cept­ably quiet and the si­lencer does not re­strict the en­gine per­for­mance at high revs.

For the rest it is worth not­ing the sub­stan­tial sump guard, which is dou­ble thick­ness un­der the vul­ner­a­ble lower sec­tion. A Sherco al­loy side stand and a mod­ern chain ten­sioner with an al­loy rear mud­guard mounted on short brack­ets fin­ish the good looks.

The more you look round the ma­chine the more you see the at­ten­tion to de­tail is ex­cep­tional. All the fas­ten­ers are very ‘trick’, with lots of gold an­odised al­loy spac­ers to give a smooth un­clut­tered look.

En­gine De­vel­op­ment

The en­gine is much more stan­dard but it is the small hid­den de­tails that make the dif­fer­ence. It has been un­der de­vel­op­ment for a cou­ple of years to iron out the in­evitable is­sues of con­vert­ing a road mo­tor­cy­cle en­gine for tri­als use. For a start it is the full 500cc power plant as op­posed to the more com­monly used 350cc unit con­struc­tion mo­tor. The pis­tons are the low com­pres­sion 7:1 type by Tri­umph. The camshaft is also the ‘cook­ing’ road ver­sion and the pushrods act upon a smaller 350cc (15/16”) in­let valve com­bined with the large 500cc ex­haust valve. This so­lu­tion took some time to ar­rive at and Mark thinks it is the big­gest sin­gle im­prove­ment he has made to cure the ‘cough’ that some­times plagues four-stroke en­gines at low rpm.

Another im­prove­ment was the use of Cham­pion N12YC spark plugs. As there is no vis­i­ble dis­trib­u­tor or points hous­ing this can mean only one thing: elec­tronic ig­ni­tion; in this case it comes cour­tesy of Elec­trex. The car­bu­ret­tor is an Amal con­cen­tric 22mm us­ing the fol­low­ing jet­ting: Main 180, pi­lot 106, nee­dle 2, slide 3. The clutch is stan­dard Tri­umph is­sue and uses a stan­dard-tooth du­plex en­gine sprocket. The gear box is a spe­cial low ra­tio unit, with first and sec­ond gears be­ing close to­gether mean­ing that you have a choice. How­ever, Mark nor­mally uses first gear for most sec­tions. The fi­nal sprocket ra­tios are a 15 tooth gear­box and an ex­tra-large 54 tooth on the rear wheel; the ma­chine is slow on the road but per­haps still not quite slow enough in sec­tions.

Rip and Roar

I had the plea­sure of rid­ing around with Mark and Steve at the Soultz Two Day Trial so my im­pres­sion on how the ma­chine rides is based on my own time rid­ing it, and watch­ing closely how it re­acted when be­ing rid­den by a good rider on the high­est level of dif­fi­cult sec­tions. Mark’s record speaks for it­self; he was a top school­boy tri­als and mo­tocross rider and then com­peted for many years in Bri­tish Cham­pi­onship En­duro. In re­cent years he has won the highly com­pet­i­tive Sammy Miller Twin-Shock Cham­pi­onship twice, as well as the 2014 FIM Clas­sic Trial Cup for Pre-65 ma­chines.

Start­ing the ma­chine is easy, as a slow push on the long kick-start fires the en­gine up quickly and once fully warmed it set­tles into a steady bur­ble. The clutch lever is nice and light and the first gear snicks in with al­most no sound or re­ac­tion, it is so smooth and slick I had to check it a cou­ple of times to make sure we were in gear! First gear is quite short with revs climb­ing quickly; you do not get the thump, thump sound of a big sin­gle where you can count each power stroke but a much more fre­netic roar of a ‘rac­ing’ en­gine. The revs rise and fall quickly, mak­ing it much more mod­ern in its feel. The rid­ing po­si­tion is also sur­pris­ingly mod­ern, with the low mounted footrest and higher bars fall­ing nat­u­rally to hand.

Look­ing down from the cock­pit past the slim al­loy tank re­veals a fair amount of en­gine stick­ing out on each side, with the Si­amese ex­haust sys­tem dom­i­nat­ing the left. This is some­thing of an op­ti­cal il­lu­sion as in re­al­ity the en­gine is no wider than the rear sus­pen­sion units. Hap­pily the cen­tre of grav­ity seems quite low, with no sen­sa­tion of fall­ing into cor­ners. The steer­ing lock is ex­cel­lent and the tight­est of turns are fea­si­ble. It is pos­si­ble to use the clutch as it feels very mod­ern in its ac­tion, with no grab or slip, how­ever the en­gine has more than suf­fi­cient torque to blast up a climb should you ride in the older style. It takes some time to re­cal­i­brate your rid­ing style as en­gine brak­ing is quite strong but also smooth. The ma­chine de­cel­er­ates nicely when you snap the throt­tle shut and makes up for the dif­fi­cult to reach and spongy rear brake. For me this is the worst as­pect of the ma­chine as a long cross-over ca­ble takes the left side drum to a right side foot­brake. In the end I just for­got about it and used the en­gine.

Powwweeerr!!!!

There is one thing a 500cc tri­als en­gine on full song is not short of, and that is power; open the throt­tle and it sets off - and boy, what a noise! It is quite ad­dic­tive and I can ad­mit I am a con­vert to the ex­pe­ri­ence. I did once own an im­mac­u­late Fred Hardy 350cc twin but could never bring my­self to use it in anger as it was so nice.

The only thing that you need to think about in ad­vance is the need to pop the front higher than nor­mal and pay at­ten­tion to not catch­ing the sump guard on rocks, as the ma­chine feels long, low and wide. You can eas­ily lift and float round the front wheel thanks to the amaz­ing power de­liv­ery; a pe­riod of adap­ta­tion is re­quired but once you learn how to use this fea­ture it makes life eas­ier. The sus­pen­sion is very com­pli­ant and works per­fectly well go­ing up­hill, the Rock­shocks are ex­cel­lent and keep the Miche­lin X-Light tube­less rear tyre in con­tact with the ground and grip­ping away. I thought that the side­wall may be too flex­i­ble but in re­al­ity the mod­ern tyre is ex­cel­lent on such an old girl. The top mount­ing point of the rear sus­pen­sion is in­te­gral with the rear frame, and as such slid­ing back on down­hills is much eas­ier as there is not the lump of the top mount­ing as found on other ma­chines, a small de­tail but no­tice­able. On de­scents the front fork springs seemed too soft with such a heavy pack­age of man and ma­chine, and they bot­tomed out fairly eas­ily. Mark con­firmed the sen­sa­tion and said he has fit­ted the heav­i­est rate ‘Mag­i­cal’ springs avail­able but it was still not quite enough.

So there you have it a fan­tas­tic piece of kit. There is no doubt Mark has cre­ated a su­perb weapon that is clearly very ca­pa­ble in the right hands and is much more docile than you would first imag­ine. The time, ef­fort and frus­tra­tion that goes into get­ting a spe­cial to­gether is well re­warded when it works as well as this one. It is also clear that ob­servers and spec­ta­tors alike en­joy watch­ing it and lis­ten­ing to the rip­ping and snarling through sec­tions as it is a pretty unique au­ral ex­pe­ri­ence.

My thanks go to Mark for trust­ing me with his ‘Spe­cial’ ma­chine, and to Steve for man­ning the cam­era.

As Tri­umphs are renowned for run­ning hot, a trick oil cooler from a Honda XR400 model tucks neatly around the steer­ing stem, feed­ing cooler oil to the rock­ers. The Si­amese ex­haust sys­tem dom­i­nates the left hand side. It’s the full 500cc power plant as op­posed to the more com­monly used 350cc unit con­struc­tion mo­tor.

Look­ing down from the ma­chine past the slim al­loy fuel tank re­veals a fair amount of en­gine stick­ing out on each side. This is some­thing of an op­ti­cal il­lu­sion as in re­al­ity the en­gine is no wider than the rear sus­pen­sion units.

Rear sus­pen­sion is taken care of by some cus­tom-built black an­odised, and sub­tly en­graved, Rock­shocks sus­pen­sion units.

The forks are Royal En­field low­ers with a slight lead­ing axle, and the in­ter­nals are by Be­tor from an Ossa Grip­per.

To­tal con­cen­tra­tion for our ‘Test Pi­lot’.

The sub­stan­tial sump guard plays its part.

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