MTA Queensland five-rings logo

WHAT IS A CRANKSHAFT AND WHAT IS ITS JOB?

The crankshaft is the engine component that converts the vertical movement of the pistons into the rotational movement required to move a vehicle. The energy of the rotating crankshaft is passed through the flywheel and transmission system, then through the driveshaft (on rear-wheel drive vehicles) or transaxle (on front-wheel drive vehicles), and on to the drive wheels that move the car.

The crankshaft is a heavy-duty piece of kit, usually made of steel or iron, that sits at the bottom of the engine. It is coupled to the base of the pistons via connecting rods that attach to crank pins at points that are offset, in a zig-zag shape, from the crankshaft’s centreline. This set-up is what enables the vertical movement of the pistons to spin the crankshaft and create rotational energy.

While the crankshaft is responsible for creating this spinning energy, it does perform other tasks. On the crankshaft end opposite the flywheel is a pulley to which the drive belt is attached. This drive belt feeds off the movement of the crankshaft and powers various components located at the front of the engine, including the alternator (which provides electric power when the vehicle is moving), the air conditioning compressor, and power steering pump, amongst other items.

The crankshaft’s movement is also directly linked to the input of fuel and air into the cylinders via its connection to the camshaft via the timing belt. The synchronisation of the movement of the crankshaft and camshaft is critical to an engine’s performance.

WHAT CAN GO WRONG?

A crankshaft is heavy and extremely rugged and is unlikely to break or crack unless it is submitted to the most extreme forces and pressure. However, it can happen and if it does the vehicle will not be going anywhere and may require a complete engine tear down and inspection, perhaps even an engine replacement,

What is more likely to happen is the failure of peripheral components critical to the crankshaft’s performance. These faulty parts can also lead to calamitous damage, but they can be repaired or replaced if the problem is caught early enough.

CRANKSHAFT SEAL: As with all moving engine parts, a lubricant is required to ensure the crankshaft’s smooth operation. Should a crankshaft seal crack or break, oil can escape and, if left unresolved, the resultant friction and heat can bend and severely damage the crankshaft.

HARMONIC BALANCER: This component sits at the pulley end of the crankshaft and is designed to absorb engine vibrations. Should it fail, the resulting increase in vibration and shaking can damage the crankshaft and other components attached to it.

CRANKSHAFT SENSOR: The crankshaft sensor is an electronic device used by a vehicle’s engine management system to monitor the position and speed of the crankshaft. The system uses this data to determine when to produce the spark to ignite the fuel and air mixture in the cylinder. Should a crankshaft sensor be faulty, the car may be difficult to start or may not start at all.

BEARINGS: Crankshaft bearings allow for the crankshaft to move and rotate smoothly, reducing friction between it and the stationary engine block above it that contains the pistons. Should these bearings fail – they can be damaged by dirt and debris contaminating the lubricating oil, or when a leak has left the system without enough oil – then pressure and friction can build up to such a degree that serious damage can occur.

All of these issues will lead to catastrophic engine damage if ignored. If the crankshaft is not balanced correctly, if the bearings fail, or vibration is too severe, then damage can travel not just from the crankshaft but on through the engine to the connecting rods, the pistons, the valves . . . in short, catastrophe.

SYMPTOMS & COSTS

Things to look out for are uneven performance, engine knocking sounds, engine misfires, low oil pressure readings, intermittent stalling, and increased vibration felt through the vehicle. These can all indicate an issue with the crankshaft system.

If the crankshaft itself is where the problem lies, then the cost can be hefty. A crankshaft replacement is a major repair job requiring a full day or more of a qualified mechanic’s time. If the problem is with a peripheral component, then the time and cost involved will be less. To ensure a less expensive solution, the symptoms mentioned above cannot be ignored. A qualified mechanic will be able to diagnose and track down the exact problem and ensure that any repair or replacement is done correctly.

9 Jan 2020