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Merco 61 Mark 2

Originally published in 'Aeromodeller', July 1966.

Latest Engine News

Merco Mark Two

The number of new or improved engines that have I been announced lately has been quite large; more, in fact, than we can hope to cover adequately in the "latest Engine News" series. A sizeable proportion of these engines, however, are R/C units and, in order to make room for those motors of greater interest to our free-flight and control-line modeller readership, detailed descriptions of R!C engines-particularly the specialised "multi" type power-plants-are being switched to our companion journal, "Radio Control Models & Electronics".

However, particularly in view of the fact that, nowadays, new British engines appear somewhat less frequently than new imported ones, we are starting this month's L.E.N. with a brief description-pending a full report when a test engine becomes available of the Merco 61 R/C Mark 2.

When the Merco 49 R/C appeared a little over four years ago, it rapidly became accepted as the Number One R/C multi engine in the U.K. and also enjoyed a quite considerable reputation overseas. The same can be said for the 61 model that became available in 1963-64 and we have no doubt that the new Mark 2 will continue to uphold British prestige, despite what may prove to be strong opposition from new foreign products.

The Merco's most impressive successes have actually been in American hands, namely Ralph Brooke's 1965 World Championship win and Maynard Hill's world records in the duration and distance categories. Some of the modifications made to the latest Merco have, in fact, resulted from suggestions from modellers in the U.S.A.. including Maynard Hill, who contributed the idea of using bronze bushes, with oilways, in both ends of the connecting-rod.

The piston is also now fitted with bronze bushes in the gudgeon-pin bosses to reduce wear. A slightly smaller diameter gudgeon-pin has been adopted to enable the bushes to be accommodated in the piston and the pin now has bronze end pads.

Externally, the most obvious change is the adoption of a new cylinder bead having twin glow plugs. It is necessary to energise only one plug to start the engine, of course, and the plugs used are standard type since it was found that, with the twin plug head, no advantage was gained by using idle-bar or shielded types.

The Mark 2 has been under development for the past eighteen months or so, during which time Dennis Allen and production man Ron Ward have made innumerable flight tests. Experimental engines were also used by the entire British team at the 1965 World R/C Championships. The power of the Mark 2 is said to be slightly increased, but the major advantage of the new model is in its improved idling reliability and greater tolerance to variations in the tank position.

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