Derby Sparking Plugs

The request for information on the sparking plugs used in the Derby engine regularly occurs and is a source of discussion at many a Club gathering.

There are two distinct camps on the solution to replacing the original style of the Long Body(LB8 Champion) plug which falls into the NGK 6 range with the body providing a substantial heat reservoir to balance the generally unsuitable harder 6 range of plug. They are with spacer or without spacer.

The spacer, usually made from copper, has two functions, it allows the use of a long reach plug to be positioned with the tip in the same position in the combustion chamber as the original LB series plug and it also positions the hexagon for the plug spanner in an accessible place for a socket to fit the hexagon and not foul the head whilst tightening or removing the plug.

The other way of achieving the same positioning of the tip of the plug is to use a conventional reach plug with no spacer(obviously!) but this requires a suitable plug spanner to gain access to the more recessed hexagon on the plug.

Ken Lea recommends NGK B5HS with the conventional electrode arrangement or BP5HS with projecting electrodes without a spacer. It is interesting that the 5 range is more suited to the Derby engine in this configuration and as a "softer" or hotter plug it reduces the possible "wetting" or misfiring that can occur.

Ken will be producing a definitive article for this section in the coming months.

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