Bonhams engine RHS high res

Ernest Henry designed, four-cylinder desaxé (reducing thrust against cylinder wall during the “power” stroke) cast-iron monobloc set on a separate barrel-shaped cast-aluminum crankcase mounted directly on the chassis frame.
Twin overhead camshafts carried in split housings on the fixed cylinder head and operate the sixteen valves through thimble tappets. Four valves per cylinder 60 degrees asymmetrically inclined (inlet 20 degrees and outlet 40 degrees from vertical). The double valve springs secured by split, tapered collets and collar.
Crankshaft is a balanced built-up type running in three ball bearings. Oil pipes pass externally along the webs of the shaft and held in place by liberally drilled, semi circular steel plates screwed to the webs to counteract centrifugal forces acting upon the pipes.
Steel, H-section, fully machined connecting rods are fitted with four big-end bolts. Plain white metal big-end bearings and bronze bushes small-ends were employed. Access for fitting of the big-ends is provided by two panels offside below the exhaust ports. Domed aluminum pistons with two compression and one scraper ring.
Train of ten cascading gears at front of the engine operate the camshafts, magnetos, oil and water pumps. The crankshaft gear drives the two magneto gears at crank speed. The two to one speed reduction to the camshafts takes place at the first stage of the gear train; all the remaining gears between the first intermediate gear and the gears at the camshafts are idlers.
Bore and stroke 68x136mm, capacity 1975.6cc.
Timing: inlet valve opens 10 degrees before TDC and exhaust valve closes 18 degrees after TDC; Inlet valve closes 30 degrees after bottom centre and exhaust valve opens 52 degrees before bottom centre. Inlet valve opening period 220 degrees, exhaust valve opening period 250 degrees. Maximum ignition advance 35 degrees. Tappet clearance 006” and 008”. Piston speed 3792fpm @ 4250rpm. Compression 6.5 to 1 in the Grand Prix but 7.6 to 1 with different pistons in post-Works Brooklands racing.
Power output 88bhp at 4200rpm. Maximum rpm on bench test 4600. Max speed approximately 100mph.
Petrol consumption approximately 13m.p.g. RAC rating 11.4hp