DU­CATI’S FIRST 350

Cham­pion idea made real in the 1960s

Classic Racer - - FRONT PAGE -

Back in 1960, the biggest mo­tor­cy­cle model that Du­cati made was just 200cc, so most peo­ple would have con­sid­ered any­one talk­ing of turn­ing that lit­tle bike into a 350 racer to be cer­ti­fi­ably in­sane. But suc­cess­ful Cal­i­for­nia racer, Frank Scur­ria, saw po­ten­tial where oth­ers thought none ex­isted and be­gan a project that even­tu­ally saw him build­ing what was ef­fec­tively the pro­to­type of the 350cc road ma­chines that Du­cati sold by their thou­sands in the late 1960s and early 1970s. Frank was a Cal­i­for­nia road rac­ing cham­pion in the Six­ties and even came to the UK mid-decade with his Manx Nor­ton to per­form with dis­tinc­tion on the Bri­tish short cir­cuits. Af­ter re­turn­ing to the States he was a win­ning driver on the Cal­i­for­nia car rac­ing cir­cuits be­fore re­tir­ing from rac­ing to join the Los An­ge­les Po­lice Depart­ment – ‘to pro­tect and serve’ as the LAPD motto says. For much of his time with the depart­ment he did that as an un­der­cover nar­cotics agent. Then, af­ter he re­tired from the LAPD, rather than just sit back and draw his pen­sion, he went to the con­flict in Kosovo with one of the pri­vate se­cu­rity agen­cies. Fi­nally, Frank de­cided that enough ex­cite­ment was enough and he came back to Cal­i­for­nia where he took the lids off the pack­ing cases that con­tained the parts of his 1963 Du­cati 350 racer and be­gan a su­perb restora­tion of a bike that is now one of the most sig­nif­i­cant Du­cati mo­tor­cy­cles in ex­is­tence. Frank was a typ­i­cal Cal­i­for­nia hot-rod­der type, who loved rac­ing any­thing with wheels; any­where, any time. There are some very nice canyon roads in the San Gabriel Moun­tains above his home­town of Glen­dale, in­clud­ing the well-known An­ge­les Crest High­way that was free of heavy traf­fic and a great train­ing ground for a would-be road racer. An­other big help in this re­spect was that the ZDS Mo­tors shop was in Glen­dale and was the West­ern States sub-dis­trib­u­tor for Ber­liner Mo­tor Cor­po­ra­tion, the USA Du­cati im­porter at that time. ZDS owner Bob Blair had been a speed­way racer in his youth so he un­der­stood the need for speed! Frank bought his first Du­cati from ZDS in late 1958 – a 200cc Su­per Sport. With a bore of 67mm and a stroke of 57.8mm, this was the largest en­gine Du­cati made at that time and it was with that lit­tle bike that the story of the first 350 Du­cati be­gan. Frank started rac­ing in Fe­bru­ary 1959, rid­ing the 200cc Du­cati in the 250cc class and he was soon look­ing for a way to over­come the ca­pac­ity dis­ad­van­tage. This turned out to be a sim­ple prob­lem to solve thanks to Al­lan d’alo, the man­u­fac­turer of ARD Mag­ne­tos. He had used his abil­i­ties as a ma­chin­ist to ex­tend the stroke of his own Du­cati to 68mm. With the cylin­der bore also be­ing 68mm, this made for a ‘square’ en­gine with a ca­pac­ity of 247cc. The only other mod­i­fi­ca­tion needed was the mak­ing of an ap­prox­i­mately 00.200in thick alu­minium plate spacer that was po­si­tioned be­tween the crank­case and the base of the cylin­der to raise the head and cylin­der to com­pen­sate for the in­crease in stroke. Oth­er­wise, it was a straight­for­ward job to make a full 250 out of a 200 us­ing Al­lan’s mod­i­fied crankshaft.

FRANK BE­GAN A SU­PERB RESTORA­TION OF A BIKE THAT’S NOW ONE OF THE MOST SIG­NIF­I­CANT DU­CATI MO­TOR­CY­CLES IN EX­IS­TENCE.

Frank used one of th­ese to build his own 250cc mo­tor and duly won the Amer­i­can Fed­er­a­tion of Mo­tor­cy­clists 250cc Cham­pi­onship in 1961. He re­mem­bers: “It was late in that sea­son that the project to build a 350 Du­cati got started, as I had no­ticed dur­ing prac­tice ses­sions that, on my lit­tle 250, I could keep pace with many of the 350s. “For the next event, there­fore, I bor­rowed an over-bored (to 69mm) cylin­der and pis­ton from Bob Blair’s per­sonal desert bike and ex­changed them with my pis­ton and cylin­der be­tween races. That made my bike 254cc and el­i­gi­ble for the 350cc race, in which I fin­ished a close sec­ond be­hind an AJS 7R, thus re­in­forc­ing my com­mit­ment to build­ing a Du­cati 350”. In late 1961, Du­cati came out with an over-square 250, with a bore of 74mm and with the same 57.8mm stroke as the 175/200 bikes. For 1962, Frank would be rac­ing a new 250 For­mula 3 Du­cati for Ber­liner and ZDS, which only had to be main­tained, so he had time to think about build­ing a full 350 but us­ing the new over-square 250cc en­gine as a start­ing point. He re­calls: “At the first op­por­tu­nity I dis­as­sem­bled one of the new over-square en­gines and, af­ter mea­sur­ing ev­ery­thing, I knew a full-size 350 Du­cati was pos­si­ble. The biggest bore I could have with­out mak­ing the cylin­der liner too thin was 76mm. With a bore of 76mm and a stroke of 76mm, I would have a ‘square’ 344cc en­gine. “The ob­vi­ous plus for a 350 Du­cati was its lighter weight com­pared to a 350 Manx or a 7R; both of which weighed in at about 300lb. I was sure I could build a 350 Du­cati that was 50 to 60lb lighter than that. “Now fully com­mit­ted to the 350 project I ac­quired a com­plete new 1961 250 Diana, took the crank to Al­lan d’alo and had him change the stroke to 76mm. Al­lan also made an ex­ten­sion for the cam drive shaft, which was, of course, too short in stan­dard form. A cylin­der spacer and a spacer for the base of the cam drive shaft cover, each ap­prox­i­mately 00.360in thick, were also nec­es­sary to match the cylin­der po­si­tion to the longer stroke. “Mean­while, Bob Blair had Borgo Pis­ton in Italy made a batch of 76mm pis­tons. Th­ese pis­tons were cast­ings rather than be­ing forged, so they were not as strong, but we only had one pis­ton fail­ure and that came much later, af­ter a lot of test­ing and more than a full sea­son of rac­ing. “I then found out about the most sig­nif­i­cant short­com­ing of any Du­cati of the bevel-drive pe­riod – the cylin­der head ports. I took the bare head to my friend, C R Ax­tell. When it came to tun­ing en­gines, he was the best around. Ax de­signed and built his own flow-bench in the 1950s and be­came the ab­so­lute mas­ter of un­der­stand­ing air­flow through a four-stroke en­gine. “He looked at the Du­cati head from all an­gles and said: ‘You can make this a lit­tle bet­ter, but you’ll never make it re­ally good – this head doesn’t have enough ma­te­rial around the ports to get the shape you need.’ Any­way, I did what Ax sug­gested I do to make the head bet­ter and this did im­prove the air­flow.” Chang­ing the in­take port an­gle was the biggest mod­i­fi­ca­tion Frank had to make to the cylin­der head and this took con­sid­er­able work. Be­fore work be­gan on the port it­self, he made a new car­bu­ret­tor mount in the form of a thick wedge-shaped flange ta­pered in two planes and welded to the cylin­der head. This re­duced the in­take port an­gle from 9° to 3°, which may seem counter-in­tu­itive but, as

Frank ex­plained, down­draft is not, in fact, the most im­por­tant fac­tor in in­take air­flow. What is most im­por­tant is the shape of the port and the an­gle of the port in re­la­tion to the valve, not the hori­zon. Very lit­tle ma­te­rial came off the floor of the port near the valve – just enough to re­move the ir­reg­u­lar­i­ties. The ma­te­rial sup­port­ing the valve guides re­mained in place in the roof of the ports, and the valve guides them­selves were left in­tact rather than be­ing ground down to be flush with the top of the port. This gave much more sup­port to the valves, and re­duced the chance of the top of the port crack­ing and suck­ing oil through the in­take port and into the com­bus­tion cham­ber. Be­cause the 13⁄ 8in Amal GP2 car­bu­ret­tor fi­nally used was big­ger ex­ter­nally as well as hav­ing a big­ger choke size than the smaller Dell’or­tos, it cleared the frame at an an­gle out to the right side. This was, in fact, a ben­e­fit as the new an­gle gave more of a swirl of the in­go­ing fuel/air charge. So that the rider’s knee would not in­ter­fere with the flow of air en­ter­ing the car­bu­ret­tor, a guard plate was spe­cially shaped and fit­ted to the carb’s air trum­pet. “Race cams for Du­catis were very hard to come by in those days,” re­calls Frank. “So the first camshaft I used was a stan­dard one with the lobes built up by weld­ing on more me­tal and then re­ground to For­mula 3 specs. A later and much bet­ter cam was the Du­cati ‘race kit cam’ or Day­tona cam. Its tim­ing was the same as the F3 cam, but it pro­vided more lift. “The cylin­der was bored to 76mm and the crankshaft stroke in­creased to 76mm. The con­nect­ing rod was X-rayed, pol­ished and shot-peened. The pis­ton was made as light as pos­si­ble and the bot­tom of its skirt was knife-edged. From the 250cc F3 en­gine we took the in­ter­nally ta­pered, and lighter, wrist pin (the gud­geon pin to you Brits!) and the pis­ton squish clear­ance was set at 0.038in. The com­pres­sion ra­tio was 10.5 to 1.” A ma­jor mod­i­fi­ca­tion that Frank made was to dis­card the stan­dard oil pres­sure rout­ing that went to the cylin­der head from the oil pump in the crankcases via the cylin­der cast­ing. In­stead, he mod­i­fied the tim­ing gear/oil pump outer cover so that the oil pump could feed di­rectly through an ex­ter­nal steel-braided pres­sure line to a one-off, cam-bear­ing hous­ing on the left side of the head. Two ex­tra oil drains were fit­ted, both on the left side of the head. They, along with one of the ex­ist­ing drains from the right side, drained into a baf­fled air/oil sep­a­ra­tor and breather com­bi­na­tion. This air/oil sep­a­ra­tor fit­ted into the threaded hole in the crank­case used for the al­ter­na­tor/mag­neto ca­ble on the stan­dard en­gine. The orig­i­nal crank­case breather tube did duty as an aux­il­iary breather. Frank also dis­carded both the orig­i­nal ig­ni­tion sta­tor and its heavy fly­wheel and fit­ted con­stant loss bat­tery ig­ni­tion in­stead. He re­tained just the brass cen­tre of the ig­ni­tion fly­wheel and used it purely as a spacer for the crankshaft pri­mary gear. “With­out the fly­wheel, en­gine ac­cel­er­a­tion speed was very fast,” says Frank. “But if I was to miss a gearshift, then the en­gine would cut out equally quickly!” “When it came to the ex­haust sys­tem, I had no idea where to start. There was never a 350 Du­cati be­fore this one so there was no­body to go to for ad­vice! The only way would be trial and er­ror. I tried var­i­ous ex­haust pipe di­am­e­ters of 15⁄ 8in and 13⁄ 4in with the fi­nal one be­ing a 15⁄ 8in pipe as it came out of the head, then open­ing out to 13⁄ 4in. The length of the var­i­ous ex­haust header pipes that I tried was about 32 to 34in and I ex­per­i­mented with mega­phones from var­i­ous other bikes. I fi­nally set­tled on a mega­phone de­signed by CR Ax­tell. “Fi­nally, a five-speed trans­mis­sion would have helped, but since the en­gine was from a 1961 Du­cati, I was stuck with only four.” Some of the en­gine test rides for the new bike took place (il­le­gally!) on the ser­vice road next to the Los An­ge­les River, next to the In­ter­state 5 Free­way where it goes through Glen­dale, just a mile or so from the ZDS shop. “The ser­vice road gate was al­ways locked so that unau­tho­rised cars couldn’t get in and use the road for il­le­gal drag races,” says Frank. “How­ever, a mo­tor­cy­cle with clip-on bars could just squeeze through the gap at the gate and onto the ser­vice road. I could make a cou­ple of high-speed passes and then scoot be­fore the po­lice came. I would be pass­ing cars on the ad­ja­cent free­way and go­ing a lot faster. As you can imag­ine, a small mo­tor­cy­cle go­ing at over 100mph caused quite a few ‘dou­ble-takes’ from driv­ers of the cars that I was pass­ing on the ad­ja­cent f reeway. On one oc­ca­sion, one of th­ese was a Cal­i­for­nia High­way Pa­trol of­fi­cer giv­ing me a w wide-eyed stare! For­tu­nately, the LA River w was be­tween us and I had time to es­cape b back to the ZDS work­shops… “There­after, most test­ing was at Wil­low Ssprings Race­way, thus avoid­ing the pos­si­bil­ity oof me be­ing ar­rested on the roads of Gglen­dale! In those days, Wil­low Springs was ju­ust 2.5 miles of race­track in the mid­dle of oopen desert, with­out fences or bar­ri­ers. “We could drive out there in the mid­dle of the week and test all day free of charge, as there was never any­one around to stop us.” From the be­gin­ning Frank found the D Du­cati 350 en­gine to be strong – and it got p pro­gres­sively stronger. The devel­op­ment of t he bike was con­tin­ual and, in ad­di­tion to the e en­gine mod­i­fi­ca­tions, he tried three dif­fer­ent chas­sis com­bi­na­tions.

AS YOU CAN IMAG­INE A SMALL MO­TOR­CY­CLE GO­ING AT OVER 100MPH CAUSED ‘DOU­BLE-TAKES’ FROM DRIV­ERS OF THE CARS I WAS PASS­ING

Frank Scur­ria on the Du­cati 250 F3 that gave him the idea for the hike in ca­pac­ity. Words: Bruce Cox Pic­tures: Ar­chive im­ages and mod­ern im­age of Frank Scur­ria cour­tesy of the Frank Scur­ria col­lec­tion, stu­dio im­ages of the 350 by Phil Ayns­ley The pro­to­type was the cre­ation of a Cal­i­for­nia road race cham­pion.

Scur­ria on the 350.

Even on the 250 Frank was rapid, es­pe­cially on fast, flow­ing cir­cuits.

Newspapers in English

Newspapers from UK

© PressReader. All rights reserved.