Peake No.4 is a limited edition of 11 engines of distinctive design, this being serial number 2. It is a beam engine with sun & planet gearing to drive the flywheel.
The single acting fixed cylinder is 8mm bore and 13mm stroke. The piston is connected to the beam via a connecting rod which is pivoted on the beam at the top end and to a pin inside the piston at the lower end. The connection to the flywheel shaft is via the beam and a pair of gears in a sun & planet configuration. This means that the flywheel rotates at twice the rate of the piston. This arrangement was the invention of Boulton & Watt and it's main purpose was to circumvent the patent for the simple crank, already taken out by a competitor. It increases complexity and has no intrinsic advantage over a crank other than the increased speed of the flywheel. The steam valve, mounted at the bottom of the cylinder, is moved by an eccentric which is mounted on the flywheel shaft but rotates with the primary "planet" gear, thus keeping in time with the piston.
The main bearing is fitted with an oil cup. The flywheel is 33.5mm diameter and has a small convex pulley mounted adjacently. This type of pulley is suitable for flat belting. The flywheel shaft is supported by an ornate machined pillar mounted on a wooden base, along with the beam pillar and the cylinder.
The bottom picture on the left is a scan of the "Certificate of Authenticity".