The Thomson cage with 16 rolls, diameter 20 mm (mark #38 for the engine) KA100, No 80 for X30) is a needle bearing mounted on rod foot The crankshaft. This room ensures the mobile connection between the rod andpiston axis, a point subjected to a very high load and extreme rotational speeds.

Function of Thomson cage

Thomson cage contains 16 cylindrical rollers very fine (also called needles) arranged around the piston axis. Their role is to enable fluid and precise rotation of the rod foot around this axis, while reducing friction and wear between metal surfaces.

During engine operation:

• The piston rises and descends to very high frequency (more than 250 times per second),
• The rod foot rotates constantly around the piston axis,
• The Thomson cage evenly distributes the forces on the rollers, ensuring free and controlled movement.

Without it, metal-metal contact would quickly destroy the axis and the rod foot.

Characteristics

• Type : needle cage (16 rolls) known as "Thomson".
• Inner diameter : 20 mm (corresponding to the piston axis of X30 and KA100).
• Materials : high strength treated steel for rollers, steel or brass cage depending on the versions.
• Operation : continuously lubricated by the air-gasoline-oil mixture.
• Mounting : inserted in the small eye of the rod, between it and the piston axis.

The dimensioning and machining accuracy of this cage is vital to maintain a perfect geometry of the crankshaft and avoid any play that would cause a rattling noise or misalignment of the piston.

Difference between X30 and KA100

Although these engines share the same principle, their cages are specific to each model :

• Benchmark (38) for KA100, adapted to the width of its rod.
• Benchmark (80) for X30, slightly different in thickness and adjustment tolerances.

They are therefore not Not interchangeable, even if the diameter of the axis is identical.

The Thomson cage is a discrete but essential element of the two-stroke engine: it guarantees fluidity of the rod movement and contributes directly to the longevity of the crankshaft. On a competitive engine such as the X30 or KA100, its condition directly affects the reliability and accuracy of the high engine.