Stepped Key

The drive cam seated on the pump shaft must transfer torque without slipping. Stepped key 40222, fitted simultaneously into the shaft groove and the cam bore groove, locks mutual rotation of both components and fixes the angular position of the cam on the shaft.

Application

The key is installed between the drive shaft and the cam bore in the Kranzle pump drive chamber. The stepped key profile means it has two different levels – each matched to the groove on its respective side: one to the groove in the shaft, the other to the groove in the cam hub. This arrangement secures the angular connection and eliminates rotational play between the shaft and the cam. It transfers engine torque to the cam, which in turn drives the pump pistons with reciprocating motion.

Symptoms – When to Replace

• Rotational cam play on the shaft – the cam moves angularly relative to the shaft when attempting manual rotation after chamber disassembly.
• Uneven or pulsating pump operation not caused by valve or seal wear – cam slippage alters the effective piston stroke.
• Visible bending, fraying, or crushing of the key after disassembly – the key is no longer transferring torque correctly.
• Worn groove in the shaft or cam bore causing the key to self-eject during pump operation.
• Characteristic knocking from the drive chamber synchronised with shaft rotation – key play causes impacts when the direction of torque reverses.

How to Select the Correct Part

The basis for selection is reference number 40222. The stepped key must fit simultaneously into the shaft groove and the groove in the cam bore – both dimensions must be compatible. When replacing, assess the condition of both grooves: a worn groove in the shaft or cam hub will cause play even with a new key. If the groove is damaged, replacing the key alone will not resolve the angular cam play.

Compatibility

Kranzle catalogue part. Used among others in Kranzle pressure washer pumps with a cam drive system. Cooperates in the assembly with cam 4005580 and the pump drive shaft. Verify compatibility with a specific model using reference number 40222 or the pump service diagram.

[faq]

How does a stepped key differ from a standard rectangular key, and can they be used interchangeably?|A stepped key has a two-level profile – each level has a different height, matched to the groove on the shaft side and on the cam side respectively. A standard rectangular key has a uniform height along its entire length. The geometric difference rules out interchangeability – a rectangular key in a groove designed for a stepped key will not fill it correctly and will not transfer torque without play.

Does knocking from the drive chamber always indicate key play, or can there be other causes?|Key play produces a characteristic knock that changes with load – under pump working pressure, as torque increases, the knock intensifies or changes character. Bearing noise is more uniform and depends primarily on rotational speed. During diagnosis, it is worth checking key play manually after removing the cam – rotational cam play on the shaft with the shaft locked unambiguously points to a problem with the key or groove.

Does a worn shaft groove disqualify the shaft, or can it be reconditioned?|With minor groove wear, reconditioning is possible by build-up welding and turning to the correct dimension, or by machining a slightly larger groove and selecting a non-standard key. With deep wear or destroyed groove geometry, shaft replacement is the safer solution. The decision depends on the extent of the damage and the availability of the shaft as a service part.

What can cause key destruction without visible groove damage?|Most commonly, drive system overloading – pump operation with blocked flow, sudden stoppage under pressure, or start-up with a frozen hydraulic system. As a component intentionally weaker than the shaft and cam, the key acts as a safety element in such situations – it fails instead of the shaft or cam. If the key has failed repeatedly without an obvious cause, it is worth checking the pump operating conditions and the condition of the safety valve. 

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