The Hedlund Engine
THE HEDLUND ENGINE
Can This Swedish Four-Stroke Halt the Screaming Two-Stroke?
AKE WREMP
HAS THE four-stroke a future in motocross, or will the two-stroke continue to scream its dominance? In Sweden, there is a man who swears by the four-stroke principle. His name is Nils Hedlund. Despite enormous successes by the Swedish Husqvarna, and other European manufacturers of two-stroke motorcycles, Hedlund is busy building new four-stroke engines, to which he has given his surname. These are beautiful dohc Singles.
Hedlund, who has worked with four-stroke powerplants for years, some time ago helped the Husqvarna factory build the engine which carried Rolf Tibblin to world championship. Later he constructed his own sohc engine, which also was used by Tibblin, and by a host of other European motocross riders.
A sample of the latest Hedlund was shown at thf* Earls Court show in London last fall. The first batch of production engines is specially designed for quarter-mile speedway racing. More than a dozen now have been built and many top riders in the Swedish speedway league are using Hedlund engines this year.
Next in production will be the motocross version of the powerplant. Basic design will be identical, but different cams and a lower piston will be used.
A gearbox is cast in-unit with the crankcase. For speedway use, Hedlund fits a countershaft and clutch. For motocross, there is a three-speed cluster within. Hedlund says that torque is sufficiently high at lower rpm that a fourth gear isn’t necessary.
Hedlund has plans for a road racing model of the engine. It is possible to fit a five-gear cluster into the gearbox, if the foot change mechanism is located outside. This engine also could be used in a high performance sports bike expressly for four-stroke addicts-such as those who bought the Norton International.
It is possible to use two cylinder sizes with the Hedlund engine. One is 80 mm in diameter, for total displacement of 498 cc. Another cylinder, with an 88-mm bore, for 602-cc piston displacement, is suitable for 750-cc FIM motocross and sidecar racing machines. Stroke with either cylinder bore is 99 mm.
Main feature of the engine is simple, plain construction. There is nothing complex or difficult to fit. Hedlund knows how busy a racing mechanic can be in the pit as race time approaches. It is possible to fit a new piston to the Hedlund in less than 45 min. Though of differing length, all crankcase bolts are of identical thread size; only a small Allen wrench is required to divide the lower end case halves. The left flywheel is marked for valve timing, ignition, tdc and bdc. A small opening in the crankcase provides access to these markings.
The engine is cast in magnesium alloy (elektron) to save weight. The complete motocross powerplant tips the scales at 88 lb. To prevent corrosion, all exposed engine components, except the cylinder barrel, are anodized in striking gold.
The dohc system is driven by a chain at the right side. The upper sprocket is fitted to the inlet shaft. Two gears couple the camshafts together. The magneto is on the left end of the exhaust valve camshaft. The Swedishmade magneto carries a low voltage coil and breaker points inside its case. A separate high voltage coil and condenser are mounted without.
All valve train components are mounted in needle bearings. The rocker arms tum in three needle bearings each. Valve clearance adjustment is through eccentric rockershafts.
The bottom half of the engine is exceptionally rigid, with numerous cast-in strengthening ribs in areas of high stress. Even the main bearings are of the needle type, with a single ball bearing added to the drive side.
Primary drive is by single-row chain, running in oil. The clutch is outside the crankcase, where maintenance can be carried out with ease. The output shaft in the gearbox is on the right side. The drive sprocket is fitted on splines and secured by a circlip.
The oil system on the motocross engine employs a Triumph pump. Hedlund believes the gearbox can carry a sufficient volume of oil for both gear and engine lubrication. The oil is pumped to the engine, then is fed back to the gearbox through a filter. If necessary, the Hedlund engine can be fitted with an external oil cooler. The speedway engine carries a simple oscillating pump for total loss lubrication.
The 80by 99-mm bore and stroke engine delivers 50 bhp at 6500 rpm on alcohol fuel for speedway racing, and 44 bhp at 6500 rpm on gasoline in motocross trim. As stated, the motocross engine weighs 88 lb., but the speedway engine, without gears, is 11 lb. lighter at 77 lb.
Engine prices, in Sweden, are approximately $670 for the speedway version, $900 for the motocross unit. The factory, AB Nils Hedlunds Motormekaniska, is at Stjarn— fallsvagen 43, 163 54, Spanga, Sweden. ■
