Big­ger isn’t al­ways bet­ter

With the cur­rent in­ter­est in smaller ca­pac­ity bikes for pre-65 tri­als, we have a look at a rather spe­cial small ca­pac­ity bike for twin­shock tri­als.

Classic Dirtbike - - Contents -

If any­one had said to me in the Sev­en­ties “what you need son is a 125…” I’d have laughed them out of the place, I knew what I needed, it was the red and black Model 199 325 Bul­taco Sherpa, be­cause that’s what ‘Vesty’ and the Lamp­kins were rid­ing and win­ning on, or so it ap­peared. The thing is with the best will in the world I’m not a ‘Ves­ter­i­nen’ or a ‘Lamp­kin’ nor I sus­pect are a great many other rid­ers, but the big­ger bikes were do­ing the win­ning and that’s what we wanted.

In some re­spects this has al­ways been the case in the com­pe­ti­tion world and de­spite a smaller ca­pac­ity ma­chine be­ing avail­able the rider would al­ways con­vince them­selves the big­ger one would be bet­ter. The ev­i­dence to the con­trary was al­ways there as Bill Lo­mas beat all the big bikes on a 200cc James in the Travers Tro­phy Trial in 1951, just to rub things in a bit Arthur Shutt took the 1953 Scott Trial on a 200cc Fran­cis-bar­nett. Then Jim Alves started win­ning awards on small Tiger Cubs, Roy Pe­plow won the 1959 Scot­tish on a Cub too so the ar­gu­ment small bikes weren’t up to the task held lit­tle truth.

Fast for­ward a lit­tle to the early Eight­ies and Fan­tic’s 200 model – ac­tu­ally 156cc – which showed small could work quite well. At that time I’d been per­suaded into the chair of an out­fit based on a 200 Fan­tic and of the two of us in the team I was the small one.

The big­ger bike wasn’t fin­ished though and Fin­nish su­per­star Yrjo Ves­ter­i­nen was de­vel­op­ing a 340 Bul­taco at Comer­fords in Thames Dit­ton while the fac­tory was sort­ing it­self out and what a fab­u­lous bike the re­sul­tant ma­chine was, as long as your name is Ves­ter­i­nen. Prob­lem was not ev­ery tri­als rider is a Ves­ter­i­nen and hav­ing rid­den it in a trial some time ago I learnt the true mean­ing of be­ing ‘over-biked’, as that par­tic­u­lar Bulto was built to Vesty’s rid­ing style and not mine. As he re­vealed later though, not ev­ery­one was con­vinced of the big­ger bike’s su­pe­ri­or­ity and a close run thing at a trial where fel­low Comer­fords’ rider Steve Saun­ders gave him a run for his money while rid­ing a 250 Sherpa set a train of thought go­ing in Vesty’s mind, which re­sulted in this neat look­ing 125 Sherpa be­ing cam­paigned by an­other Ves­ter­i­nen… daugh­ter Hanna.

Vesty felt the 125 Sherpa had some po­ten­tial if the un­der pow­ered and lazy en­gine could be pepped up a bit and some weight shifted off the bike. A 125 Model 185 came his way but it was a bit un­der­whelm­ing to say the least. “The prob­lem is the 125s didn’t have much de­vel­op­ment at the time, Mon­tesa had one on the mar­ket and Bul­taco thought they’d bet­ter put one out. I picked up a bar­rel from the 125cc Streaker model think­ing it might prove bet­ter, it was at the top end but any torque the orig­i­nal Sherpa had van­ished with the road bike bar­rel.” The idea of the 125’s po­ten­tial didn’t go away though and when Hanna got a mod­ern 125 Beta and her dad had a ride on it he couldn’t be­lieve it was just a 125. All of a sud­den there was a cat­a­lyst for the 125 Sherpa.

“It was so much bet­ter than the 125 Sherpa, yes it was a lot newer but still, I con­tacted John Lamp­kin – Beta im­porter – and asked for some in­for­ma­tion about the en­gine spec­i­fi­ca­tion which he got for me, then talk­ing to Mick Grant he pointed out we should strip the Beta and com­pare to the Bul­taco to see where the dif­fer­ences were and if the 125 Sherpa could be mod­i­fied to the same.”

What fol­lowed from this ini­tial ride on a Beta was an in­tense pe­riod of de­vel­op­ment, which by his own ad­mis­sion be­came a steep learn­ing curve for the Finn. “When I was at Bul­taco I was pri­mar­ily a rider, yes my opin­ion was wanted but I didn’t have to do the work so a lot of what has been done to this bike was new to me and I’ve learnt a lot along the way, such as mea­sur­ing port tim­ings and that sort of thing.

“This is a good point to say with­out Mick's help I couldn't have done the work, I was pretty

good at do­ing the ig­ni­tion tim­ing on a Bul­taco but the rest of the work I had no idea about,” said Vesty.

Delv­ing in to the Beta en­gine the first sur­prise was the shape of the cylin­der head. “It was like noth­ing I’d seen be­fore and the port tim­ings were nowhere near what the Bul­taco used, in fact ini­tially we felt it couldn’t work, yet it did.”

He went on to say the first task was to weld up the Bul­taco com­bus­tion cham­ber and re­shape it to the same as the Beta, this made a sig­nif­i­cant dif­fer­ence to per­for­mance but mea­sur­ing the com­pres­sion ra­tio showed it was nearly 16:1.

“Mick and I were con­vinced it wouldn’t work at such a high ra­tio but the Beta was the same and it did.” The bike was re­assem­bled and tested and what a dif­fer­ence. “I knew it was on the right track but de­vel­op­ment wasn’t hap­pen­ing fast enough and I for­got an im­por­tant les­son ‘mod­ify one thing at a time’ then you know if it is good or not good.”

The head was pretty easy to mod­ify, it’s an air-cooled two-stroke and not ex­actly dif­fi­cult to re­move. Late one Satur­day af­ter­noon CDB hap­pened to be tak­ing some scrap… er… valu­able clas­sic spares to Granty’s for some weld­ing and ar­rived just as the Bul­taco cylin­der head was be­ing mod­i­fied. In the space of a few min­utes the head was lifted, pis­ton greased, head tight­ened, liq­uid poured in, cal­cu­la­tion made, head lifted off, fit­ted in the lathe and a frac­tion skimmed off, head back on and Vesty was test­ing the bike.

Prior to the cylin­der head work Vesty told me the bal­ance holes in the crank had been plugged by Max Heyes and the crankcases had been welded up around the trans­fer ports so when the cylin­der bar­rel was dropped in it could seal the air gaps. So now the tim­ing of all five ports in re­la­tion to each other could be mea­sured prop­erly and ex­per­i­men­ta­tion could be­gin. En­gi­neer Bill Bev­eridge was happy to mod­ify cylin­der lin­ers but this started to be­come time con­sum­ing and ex­pen­sive as an ex­per­i­ment – the Bul­taco cylin­der is al­loy, the liner is more likely iron of some form – the bar­rel is heated up and a liner dropped in or pressed out. A sug­ges­tion from Mick Grant to use a Loc­tite plas­tic metal for ex­per­i­ment­ing on the in­let port speeded things up a lot and im­prove­ments were no­tice­able but still not right… at least if the view­point is a from a three-time world cham­pion.

Look­ing back at the Beta en­gine, Vesty’s at­ten­tion was on the ex­haust and the port shape plus the pipe it matched. Hav­ing an al­loy block made to repli­cate the Beta port shape made a vast dif­fer­ence, “all of a sud­den

there was torque at the bot­tom end of the range and it still revved cleanly. The ex­haust on the bike now is dif­fer­ent to the one used at the time of your photo shoot,” said Yrjo, “with the port mak­ing such a dif­fer­ence I mea­sured up the Beta ex­haust and tried to repli­cate it as best I could within the frame­work of the Bulto.” At one point ap­par­ently the pipe was mod­ded on a daily ba­sis by Barry Cham­ber­lain – Barry also did the work on our Project IT frame up at Rod Spry's place in Rawten­stall – un­til the time was reached when per­for­mance went back­wards and he knew he’d reached op­ti­mum level.

While all this was go­ing on, in or­der to im­prove the zip from the en­gine, the fly­wheel was light­ened, “maybe by a lit­tle too much,” says Vesty, “as I had to have a band put round it to stop it break­ing apart and add a lit­tle weight to pre­vent it stalling.”

Though the 125 was a proper Bul­taco it was a phys­i­cally smaller ma­chine than the rest of the range and needed at­ten­tion to the rid­ing po­si­tion and steer­ing. There was no need to – and we quote the man here – “rein­vent the wheel, we mea­sured the di­men­sions of the Beta 125 and made the Bul­taco as close to them as pos­si­ble but re­tain­ing the ‘look’ of the Bulto.” What this means is the di­men­sions such as rear wheel spin­dle po­si­tion in re­la­tion to footrest and han­dle­bar po­si­tion plus fork height, fork trail and wheel­base were repli­cated to mod­ern di­men­sions. The forks them­selves are from a 325 though with some un­known slid­ers on the bot­tom.

“I was at Telford show and saw these Be­tor slid­ers on a stand, brand-new and longer than the Bul­taco ones, I’ve no idea at all what they would have been for orig­i­nally but they gave a use­ful in­crease in fork length but needed the steer­ing head moved up the frame a lit­tle.”

As we’re talk­ing, Vesty made it clear he’s had a lot of help from a lot of peo­ple and said Rod Spry made the frame al­ter­ations early on in the process. This in­volved Rod cut­ting steer­ing head off com­pletely and reweld­ing in the new po­si­tion with a gus­set to steepen the an­gle. This al­lowed Vesty to in­crease the swing­ing arm length while keep­ing the wheel­base the same size.

“It looks as though we have repo­si­tioned the bot­tom mount on the rear dampers but in ac­tual fact it is the ex­tra length in the swing­ing arm which is dif­fer­ent though Rod did cut the frame at the mud­guard loop and move the top mount for­ward to gain more sus­pen­sion travel. I feel now this bike steers bet­ter than my own 280 and if I ever de­cide to make a new frame for the 280 I will repli­cate this one,” he says.

At my ques­tion “is that it?” Yrjo laughed and said “of course not, this is an on-go­ing process and an en­joy­able learn­ing ex­pe­ri­ence for me. For in­stance car­bu­ra­tion has been in­ter­est­ing, in your photos the 125 has an Amal Mk11 on but now has a Kei­hin 28mm flat slide but I’ve tried all sorts of other ones.”

Know­ing Vesty’s ob­ses­sion with carv­ing weight off his bikes I won­dered if the 125 was feath­erlight? “Not es­pe­cially, we cut the frame tubes off and used an al­loy bash plate which saved a lit­tle weight, then the spin­dles are all al­loy so there’s a lit­tle sav­ing there.” No su­perlight ti­ta­nium fas­ten­ers? “Not re­ally, there are a few but the sav­ing ver­sus cost would be im­prac­ti­cal, maybe I will re­duce the weight at some point but it’s about 76kg – 167lb give or take an ounce – and it started at 84kg.”

To fin­ish off, Vesty al­lowed the project was time con­sum­ing and not the sort of thing to tackle lightly, but from our point of view the re­sult is spec­tac­u­lar. “You ought to bring your 250 along and have a com­par­i­son test some time,” he said. Okay, you’ve twisted my arm, look out for the rid­ing fea­ture next sea­son. 

You want the bike where? Why? To make the forks sit cor­rectly, the head­stock was cut off, repo­si­tioned and welded up. Rear units are also Be­tor from Sammy Miller Prod­ucts.

Still 125cc and six- speed but now per­form­ing more like a mod­ern bike thanks to the ef­forts of Yrjo and Mick. Carb is now a Kei­hin. Mod­ern footrests from Apico help in the im­proved rid­ing po­si­tion. Hanna in ac­tion at West­mor­land club’s Bul­taco...

Oh, that’s why. Yes, now smile. Just be­cause you were amulti-world cham­pion doesn’t mean you can’t be bossed around by your daugh­ter… go on, get the plug changed.

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