HARRY MUNDY’S TWIN-CAM LOTUS ENGINE, BASED ON THE 1500 CORTINA BLOCK, WAS GOOD FOR A STOCK 110HP. BUT SMART TECHS HAD STEEL CAMSHAFTS MADE AND MANAGED 200HP
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!