TAKING THE ROUGH WITH THE SMOOTH

To polish or rough-up the inside wall of the cylinder? Jim Tyler investigates

Many people love to draw parallels between the design and workings of the spring air rifle, and those of the internal combustion engine, and to do so is usually a mistake, because the springer and the engine are two very different beasts.

Both have pistons and cylinders, and both compress air, but that’s about all the two have in common. For a start, a piston in a car that does 10,000 miles a year will travel up its cylinder in the region of 40 million times, whereas the piston in a much-used airgun might do 5,000 to 10,000 shots a year, and the car engine piston and cylinder have to cope with far higher pressures and temperatures than the airgun piston and cylinder, so the design criteria are very different, and so the pistons, their seals and their lubrication are just as far apart.

DESTROYED IN SECONDS

The materials used for springer piston seals would be destroyed in seconds in an internal combustion engine, and engine piston rings are typically made from cast iron or treated steel, and are harder than the cylinder wall to minimize wear, whereas airgun piston seals are nearly always much softer than their cylinders, so the two need very different lubrication. The lubrication system of the engine piston and cylinder is of necessity one of constant replenishment (oil is splashed onto the cylinder wall by the rotating crankshaft) to prolong the life of the cylinder wall because most of the oil on the cylinder wall is burned off during the combustion stroke, whereas the springer lubrication has to last for thousands of shots before needing replenishment.

In spite of these huge differences, the temptation to tap into the massive knowledge base from decades of multi-million-pound research and development of the internal combustion engine, and apply it to the spring airgun, is too much for many to resist, and the most frequent involves cylinder finish.

CROSS HATCHING