Street Machine - - Dirty Stuff -

BIl­let-steel camshafts. Why are they made? And why do we need to fit them to some en­gines?

Ever since Dr Niko­laus Otto in­vented the fourstroke-cy­cle in­ter­nal com­bus­tion en­gine, cast iron has been the en­gi­neer’s first choice for valve­op­er­at­ing camshafts. The stuff is dead easy to cast, quick and easy to ma­chine and work-hard­ens beau­ti­fully, un­til it gets about as tough as old goats’ knees.

But be­cause of en­gine de­sign­ers’ com­pro­mises, mostly with side­valve and over­head-cam en­gines, tech­ni­cians chas­ing higher power out­puts have had to go to a stronger ma­te­rial, which is where these bil­let-steel camshafts are the only so­lu­tion.

Merv Wag­gott and his Syd­ney-based com­pany Wag­gott En­gi­neer­ing were fa­mous from the early 1950s for the de­sign and man­u­fac­ture of go-faster camshafts and as­so­ci­ated com­po­nents. One of the en­gines they worked on was Henry Ford’s ‘cast-iron won­der’, the 3.6litre side­valve V8. Henry’s team had cre­ated this en­gine to be made in its thou­sands, and the 16-lobe camshaft was a to­tal com­pro­mise. They were skinny, to save on ma­te­rial, with only three bear­ing jour­nals, and the lobes were not large and close to the V where the flat-tap­pet hol­low cam-fol­low­ers worked. This de­sign was great for thou­sands of road kilo­me­tres, as long as you didn’t need to go any faster.

The speed­boat rac­ing mob wanted to fit these Canada-sourced en­gines to their mono­hulls, but with a side­valve en­gine where the cam lobe works di­rectly on the base of the cam-fol­lower, in­creas­ing valve lift means you have to grind the base cir­cle of the lobe to ef­fec­tively raise the op­er­at­ing peak. Which then re­quires the metal of the shaft be­tween the lobes to be ma­chined to a smaller di­am­e­ter to clear the cam-fol­low­ers. With Henry’s en­gine, this se­verely weak­ened the shaft, so when your mono­hull mill was pulling in ex­cess of five grand out on the wa­ter, of­ten the back of the camshaft would part com­pany with the rest of it.

Merv fixed that by ma­chin­ing spe­cial-or­der full­race camshafts out of mild steel, and never broke an­other one.

It was the same scene with many small over­head-cam en­gines. Harry Mundy’s twin­cam Lo­tus en­gine, based on the 1500 Ford Cortina block, orig­i­nally had rough-cast skinny camshafts, driven by a sin­gle-row chain. Fine, if you didn’t want any more grunt than the stock 110hp. But if you ground the cam lobes for greater valve lift and du­ra­tion and fit­ted stronger springs to con­trol that, usu­ally Ford’s stock bucket-fol­low­ers broke. You could fix that by fit­ting Alfa Romeo fol­low­ers, but then the noses tended to break off the cast-iron shafts. Search­ing for the magic 200hp, smart techs had steel camshafts made and solved the prob­lem.

An­other hap­pen­ing you get with skinny camshafts lift­ing heavy­weight valve springs is the un­wanted char­ac­ter­is­tic of shaft flex at ex­treme rpm. This was com­mon with the screamer 1.1litre Ford Formula Ju­nior en­gines of the 1960s, which could rev in ex­cess of 10,500. Their 105E camshafts had the usual three bear­ing jour­nals. With Cos­worth’s suc­cess­ful lobe de­sign of 55/86–86/55 de­grees, and high-ra­tio rocker gear in­creas­ing lobe loads, camshaft flex rad­i­cally al­tered the tim­ing fig­ures and of course, these screamer en­gines lost power. The so­lu­tion? Ei­ther fit an­other two bear­ing jour­nals, which was ex­pen­sive and in­creased fric­tion loads, or sim­ply ma­chine up a bil­let-steel camshaft.

We now have, of course, roller­fol­lower camshafts; ex­cel­lent en­gi­neer­ing, with the ma­jor ad­van­tage of the roller shapes in­creas­ing the valve open­ing area, which a flat-tap­pet cam could never achieve. But this de­sign has its roots back in the 1930s, when ex­per­i­men­tal en­gi­neers dis­cov­ered if they ra­diused the foot of their flat-tap­pet fol­low­ers, and de­signed a cam lobe com­pat­i­ble with that, they also could in­crease valve open­ing ar­eas in their side­valve en­gines. All with­out the added ex­pense of go­ing the roller road when they didn’t have ma­te­ri­als that would stand up to the strain. English Austin Sev­ens and the ad­vanced Amer­i­can Hud­son en­gines all had this fea­ture, which fol­lows on to­day in many sin­gle-over­head cam sym­met­ri­cal shapes, but these days us­ing valve rocker arms with en­gines that use shaft-mounted rock­ers to open their valves.

A few years back, I had a large in­volve­ment with the en­gine of a 1955 GP Fer­rari. This had a Lam­predi-de­signed, four-pot al­loy 2.5-litre twin­cam en­gine, with a bore of 100mm and a stroke of 75mm. This mill, which nor­mally revved to 7500 but could be screwed in ex­cess of 9000rpm if the need was des­per­ate, had to be re­built ev­ery 800 rac­ing kilo­me­tres, as the heavy­weight 14:1 pent-roof cast-al­loy pis­tons cracked around the pin bosses; if one broke, you had one de­stroyed en­gine.

That never hap­pened, but the valve-op­er­at­ing gear showed just how way-out an ex­otic en­gine could go. They had huge sodium-cooled valves an­gled 90 de­grees apart and con­trolled by dou­ble hair­pin valve springs po­si­tioned hor­i­zon­tally each side of the valve. Big al­loy cam buck­ets car­ry­ing a sin­gle bushed steel roller closed onto the cam lobes by dou­ble coil springs. And the lobes them­selves? Ma­chined onto a hol­low gear-driven steel camshaft, these high-lift lobes were only 6mm wide!

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