The spi joint 25x40x7 crankshaft X30 / KZ (reference IAME 62) is a seal mounted at each end of the crankshaft. It prevents air or oil leaks between the engine crankcase and the crankshaft, ensuring the smooth operation of the two-stroke engine.

Function of the spie joint

This seal is used for isolating the crankcase chambers the rest of the engine while allowing the crankshaft to run freely.
On a two-stroke engine like the IAME X30 or KZ, the engine crankcase is not simply a container: it is an integral part of Gas transfer circuit.

When the plunger goes down:

• it compresses the air-fuel mixture in the crankcase,
• This pressure then sends this mixture to the cylinder.

If the spi joint leaks, this compression is lost: the engine loses power, becomes difficult to start or hold. The seal also prevents the oil from mixing or the grease of the bearing from escaping outwards.

Location and characteristics

• Size: 25 mm (wrinkle) x 40 mm (outside) x 7 mm (thickness)
• Position: one on each side of the crankshaftbetween crankcases and bearings.
• Material: nitrile or viton rubber with a lip seal and one internal spring which keeps the pressure around the axis of the crankshaft.
• The direction of assembly is important: the part with the spring must be oriented Inwards the engine, to hold the pressure.

Symptoms of a defective spi joint

• Engine which takes its turns badly or suffocates at acceleration,
• Difficult start or unstable slow-down,
• Visible leaks of oil in the crankshaft,
• Mixing too poor (additional air drawn by leakage).

A simple loss of watertightness in a spi joint can be enough to make an engine unusable in competition.

The crankshaft spi joint Therefore plays a discreet but essential role: it maintains the primary compression and sealing of the housing, guaranteeing the regularity and performance of the engine. Without it, even a perfectly balanced crankshaft and bearings cannot function properly.