A Simple Top-dead-centre Indicator
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r1Nsome types of engine it is difficult, if not impossible, 'a—Ito use a wire or tither direct means for getting a topdead-centre reading from the top 'of the piston.
The accompanying sketches show a device which is•used by Simpson and Co., Ltd., of Madras; and which, the company says, gives.accurate results. The device consists, in the main, of an adaptor which takes the place of the sparking plug. To this is attached a length of rubber tubing which, in tarn, carries a short length of glass tubing.
All sparking plugs are removed and the adaptor is screwed into one of the sparking-plug holes. As the engine is slowly rotated the compressed air in the cylinder escapes through the tubing and causes air bubbles to rise through the water. .
If the .piston passes, over dead cerqre water will commence to rise in the glass tube, and when this point is reached the engine is-rocked backwards and forwards until there are neither bubbles nor a tendency for the water to he picked up.
By way of comnacnt on any such device, it is worth remembering that the angular movement of the crankshaftcan be considerable, with but only an infinitesimal movement of the piston, and where great accuracy is required crankshaft location, via the flywheel, is undoubtedly the most satisfactory means,.
Of course, wisere the piston top is readily accessible,a practicable degree -of accuracy can be achieved by using a wire, providing the engine be rocked backwards and forwards to provide a mean point en the.rod, .