A crankshaft is one of the most crucial engine parts. Located close to the oil supply, it does some real magic turning the up-and-down motion of your pistons into rotating motion that can be transferred via the gear box to the wheels propelling your vehicle forward. 

Forced by the combustion process that pushes them up and down, the pistons move connecting rods that in turn spin the crankshaft. Thanks to its special design, the crankshaft allows the connecting rods to provide circular motion which is the key to its rotation along a linear axis. Linked to the transmission via a transition clutch or torque converter the crankshaft delivers engine power to the wheels.

The crankshaft is always subjected to extreme forces while the engine is running, which is why it should be very durable and strong. For this reason it is usually cast from a piece of high-grade steel bar and then forged for extra durability. At the same time some manufacturers utilize assembled crankshafts made of several pieces of steel, while others use single-piece crankshaft fabricated from remelted steel with the help of milling machines and lathes.

On each side of the crankshaft there is a bearing, which, all together, hold the crankshaft in place inside the engine. The bearings are lubricated with engine oil, allowing the crankshaft to rotate easily and smoothly as well as to stabilize its motion and withstand huge forces created by the movements of the pistons and connecting rods.

Symptoms of a failing crankshaft

A failing crankshaft is something you’ll not be able to ignore due to the importance of its function. Here are the problems that may cause a crankshaft to fail:

  • Casting or forging defects
  • Poor lubrication
  • Worn-out bearings
  • Bearing failure
  • Incorrect bearing clearance
  • Defective bearing bores
  • Broken bearing main caps

Any of these problems can lead to a cracked or broken crankshaft. Some signs can be a knocking noise from the engine and a lower level of oil or oil pressure which will cause the check engine light to illuminate. In the worst scenario your engine will stall. 

Any of these signs should be a direct prohibition for the further use of the car. You should shut down the engine immediately and have your car towed to your mechanic for inspection and repairs.

Is there a change to fix a bad crankshaft?

Unless you’re a mechanic, don’t try to fix a bad crankshaft. This is a job for a professional with many years of experience in this field. The first thing he should do is to disassemble the engine to find out the problem. Depending on its complexity, the damage your engine received and the cost of repairs, you’ll have a couple of ways to go.

Nothing else except the crankshaft is damaged

In this case you can either replace a crankshaft with a brand-new one or have it remanufactured. The latter option is the most cost-effective way to fix the problem. Besides, you may purchase a used crankshaft if you drive a very old car with high mileage. You should also inspect the crankshaft bearings and if they’re damaged or worn-out have them replaced with new ones. 

The crankshaft and bearings are damaged

This is a more expensive scenario you may face. The forces that destroyed the crankshaft have also caused excessive wear of the bearings or made them out of round. Brand-new bearings and a new or remanufactured crankshaft will fix the problem. However, if the damage is too extensive, you might have to purchase a new or remanufactured engine, which, sometimes, may cost more than a vehicle if it’s very old and worn-out.

Not only the crankshaft and bearings, but also the top of the engine are damaged

It is going without saying that it’s the most catastrophic type of the damage that may be caused by a bad crankshaft. There is a major risk that all pistons and connecting rods as well as bearings and exhaust/intake valves have been damaged. This requires a total engine rebuild that is often more expensive than buying its new or remanufactured version. If your car still has a high value you may go that way and have your engine remanufactured or replaced with a new one.