Sirena 0-4-0VB Sentinel geared engine

Overview
A model designed by J J Constable based on his Model Engineer exhibition Championship Cup winning model (1958) of the 100hp Sentinel vertical-boilered geared steam shunting locomotive. The prototype has two cylinders 6 3/4" x 9" diameter with poppet valves with power transmitted from the engine to the axles by roller-chain and sprockets.

The model, like the prototype, is fitted with a vertical boiler. The motive power is supplied by a Stuart 'Double 10', which as the original model was fitted with slip-eccentric valve gear was modified to provide reversing from the cab using a slip eccentric rack. A 'Double 10' with full reversing and variable gear could be fitted. The engine drives the front axle through 8mm chain and sprocket with 2:1 reduction and as the rear axle is also chain driven no quartering of wheels is required.

The model uses no castings beyond those for the Stuart 'Double 10' used as the power-plant. However this engine could be replaced with a similar engine or one built entirely from stock materials.

A very detailed construction series complete with full drawings written by the designer was published in Model Engineer (UK) magazine commencing in volume 124, issue 3108, 2 February 1961 and ending in volume 125, issue 3154, 21 December 1961.

Principal Dimensions:
20 1/2" overall length.

8" wide.

11" high.

Wheels 2 5/8" diameter.

Weight in working order 23kg with a drawbar pull of 16lb allowing the haulage from a standing start of three adults up a 1:75 gradient on a 55' radius curve.

Drawing Errors
There are errors in the frame drawings as printed in Model Engineer magazine (volume 124, issue 3126, 8 June 1961, page 721). In the dimensions across the top of the frames 3/4" should read 1 3/4" and 2 7/8" should read 2 7/16". The overall length of the frames is correct as given (16"), these two dimensions were incorrectly printed.

Tanks stretchers are held in place with two 6BA counter-sunk screws, the frame-holes shown are used as pilot-holes for drilling and tapping the stretchers. The tops of the stretchers are flush with the tops of the frames.