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end of the combustion chamber, the exhaust valve at about its centre, in a direct line of fire. A defect in this engine is the angle and direction at which the main bearings are placed, which throws a great proportion of the force of the explosion on the cap bolts, instead of on the main casting; this is not good practice, especially when we consider that even with producer gas a maximum pressure of 320 lbs. per square inch is reached.

This form of engine was also made in coupled twin form, having four bearings, and on the outside of each outer bearing a heavy flywheel, and with cranks arranged so that one piston was full in when the other was full out, the cycle of operations being the same as shown on fig. 2 at C. But as it was impossible for the middle bearings to wear down at the same rate as the outer ones, because of the weight of the flywheels, and the power transmitted, the crank shaft was found to spring backwards and forwards at each throw of the crank; and unless the middle bearings were carefully and periodically lined to the outer ones, the strain would eventually have become too great and produced disastrous results. This evil has been overcome by the tandem engine, having a cylinder on each side of the crank shaft as shown at fig. 9. This type of engine does not, however, divide the work in the best possible manner, as two impulses follow each other at full power, followed by two idle strokes (see fig. 2, as shown at C). In practice, however, this makes very little difference; the advantage of two cylinders over one is that it reduces each individual impulse. Commercial requirements necessitate that sometimes the governor must cut out impulses, and as this covers a large proportion of the time of working, it is the usual condition. This being so, and taking into account the chapter of accidents which occur with the best of governors, it becomes a matter of very little importance if the impulse next to be cut out immediately follow a previous impulse, or has a single stroke between.

These engines are made in the following sizes: 60 H.P. NOM. indicating 200 H.P., and 80 H.P. NOM. indicating 250 H.P., with ordinary town gas, when running at 160 revolutions per minute. If, however, producer gas is used, the I.H.P. is less by about 15 per cent.

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Fig. 10 is an external elevation of their latest design of this size and type of engine. It differs from fig. 9 in that each engine is provided with independent gears, so that either engine can be disconnected. This design enables the makers to dispense with right and left hand combustion chambers, and makes a thoroughly well designed engine.

Fig. 11 is a 25 H.P. NOM. engine, having a cylinder 16 inches diameter and a stroke of 21 inches; it is capable of indicating as a maximum 64 H.P. The arrangement of the valves and gearing is approximately the same as in the girder type engine; but its

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own distinctive feature is the firm grip it has upon the foundation, whilst the centre line is kept very low. It, however, has the same defect in the angle and direction of its bearings as fig. 8, which neutralizes many of its otherwise valuable points. This design of bed is also used in 40 and 50 H.P. NOM. engines, the cylinders of which and combustion chambers are separate, with the exhaust valve box cast on the side of the latter. One heavy flywheel instead of two lighter ones, as in fig. 11, is used, and an outer bearing arranged to take the weight.

In fig. 12 is shown a typical engine made by this firm for

C

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