This series of articles and guides focuses on the ignition system of classic motorbikes, and in particular to perhaps the most important ignition component of all, the humble spark plug. As in other sections of this website, these articles were written primarily with respect to Matchless motorcycles (especially my own 1951 G3LS model), but much of the general information is equally applicable to other makes and vintages of motorcycle, car, lorry. tractor, lawnmower or anything else with a petrol engine!
Which spark plug?
A guide to selecting the correct spark plug for your classic vehicle (in particular for Matchless motorbikes) which includes information on the following topics:
- The original ‘KLG’ type spark plug.
- Modern NGK and Bosch equivalents.
- Spark plug code reference charts.
- Options available in other countries.
Spark plug FAQ’s
A series of ‘Frequently Asked Questions’ covering all of the important and most commonly misunderstood aspects of sparking plugs, which includes:
- What a ‘hot’ or ‘cold’ plug means.
- What a resistor plug is.
- Platimum and iridium type plugs.
- The correct tightening torque.
Spark plug heat ranges
The most common misunderstanding about spark plug is what is meant by their heat range. This article explains the difference between ‘hot’ and ‘cold’ plugs and covers:
- The physical differences between plugs.
- Optimum spark plug temperature.
- Comparison between manufacturers.
- When to change the spark plug type.