Villiers Mk 20 and 25
The Villiers Mk 20 and 25 were single-cylinder, air-cooled, two-stroke engines that were produced by The Villiers Engineering Company Ltd. of Wolverhampton, England. The Mk 20 was introduced in 1954 and was replaced by the Mk 25 in 1957. Both engines were used in a variety of motorcycles and mopeds, including the BSA Bantam, the Triumph Tigress, and the Villiers Wasp.
The Mk 20 and 25 engines were both of a similar design. They had a cast-iron cylinder barrel with a bore of 57 mm (2.25 in) and a stroke of 63 mm (2.5 in). The cylinder head was made of aluminum alloy and had a single overhead valve. The crankshaft was supported by two ball bearings and had a plain big-end bearing. The connecting rod was made of forged steel and had a phosphor bronze bush at the small end. The piston was made of aluminum alloy and had two compression rings and one oil ring.
The Mk 20 and 25 engines used a rotary valve for induction. The valve was mounted on the crankshaft and rotated in a bore in the cylinder block. The valve had two ports, one for the inlet and one for the exhaust. The inlet port was opened by the piston as it moved up the cylinder bore, and the exhaust port was opened by the piston as it moved down the cylinder bore.
The Mk 20 and 25 engines used a magneto for ignition. The magneto was mounted on the flywheel and generated a spark that was delivered to the spark plug via a high-tension lead. The spark plug was located in the cylinder head.
The Mk 20 and 25 engines used a wet sump lubrication system. The oil was stored in a sump at the bottom of the engine and was circulated by a pump. The oil was passed through a filter before being delivered to the crankshaft, connecting rod, and piston.
The Mk 20 and 25 engines were both reliable and easy to maintain. They were also relatively fuel-efficient, which made them popular with budget-minded motorcyclists. The Mk 20 and 25 engines were both discontinued in 1960, but they remain popular with classic motorcycle enthusiasts.
Villiers Mk 20 and 25 Parts manual..
Full Villiers Parts manual
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Full parts list with part numbers
Every nut and bolt covered.
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