In de­vel­op­ment

Classic Dirtbike - - Super Profile -

...... In the good old days when big fourstroke en­gines plonked their way around the tri­als cour­ses of the world 500cc units were king… okay so a few made their names on 350cc en­gines but in the main it was the big ones. Then the world saw the light thanks to riders us­ing Vil­liers en­gines but even so this wasn’t con­sid­ered a threat be­cause a 500cc four-stroke was do­ing all the win­ning even as late as 1964. Then its rider, one SH Miller nipped out to Spain, popped back with a 250 Bul­taco and car­ried on win­ning. The tri­als world started putting two and two to­gether and ended up with 250. A few years later in 1972, one SH Miller turned out on a pro­to­type Bul­taco with a 325cc en­gine and the world went big­ger again. Ul­ti­mately this in­crease in ca­pac­ity caused other man­u­fac­tur­ers to ex­per­i­ment in this area with Don Smith turn­ing out on a 400cc Kawasaki at one point and Mick An­drews too hav­ing a near-400cc Yamaha in the Sev­en­ties. Bul­taco pro­duced a 370cc model for Martin Lamp­kin and other riders on the team and for them it ended with a 340cc model at the end of pro­duc­tion. Not ev­ery­one could get on with the big­ger en­gines and of­ten while the styling and side­pan­els pro­claimed the top-of-therange big­gie what was be­ing rid­den was slightly smaller.

It seems, ac­cord­ing to a feature by Mo­tor­cy­cle’s man Peter Fraser in 1972, that while rid­ing the 250 Sherpa to good ef­fect Miller of­ten won­dered what the bike would be like with a larger ca­pac­ity. Would it, he won­dered, have the lusty low-speed torque his Ariel had? A check of the Bul­taco bar­rel di­men­sions showed there was enough meat to bore it out to 83mm di­am­e­ter – the 250 is 72mm – and this would add 75cc to the ca­pac­ity. The 83mm pis­ton orig­i­nated in the flat­track racer sold in the USA. Rid­ing the pro­to­type for a feature in Mo­tor­cy­cle Fraser found all other com­po­nents to be as the 250 ver­sion and with the bike on a weigh­bridge it was found to scale the same as the 250 or 203lb to be pre­cise.

In his test­ing Fraser reck­oned the 325 would hap­pily pull a higher gear and in fact many own­ers did just that by in­creas­ing the size of the gear­box sprocket. Fraser also found the en­gine to be nigh-on un­stal­lable and will­ing to ac­cel­er­ate from a whiff of throt­tle to launch up the test hill, the last few feet of which were ver­ti­cal. He con­cluded his test with the state­ment, “…the 325 Sherpa is a sure-fire win­ner…”. He asked Miller if there were any down­sides and the Ir­ish­man coun­tered with: “yes, it’s £10 a year road tax as op­posed to £5…”

Newspapers in English

Newspapers from UK

© PressReader. All rights reserved.