13/10/2026
Car Engine Crankshaft
What the crankshaft does
The crankshaft turns the up and down motion of the pistons into the spinning motion that powers your car. It works under huge stress, so it can run into some specific problems.
Common problems
1. Cracks and breaks. Metal fatigue is the main reason crankshafts break. Cracks usually start in high stress spots, like the curved transitions or around oil holes. Once a crack is found, the part is usually considered unfixable because it could snap without warning.
2. Worn or scratched journals. The journals are the smooth surfaces where the bearings ride. If oil runs low or gets dirty, metal rubs on metal and scratches them. That leaves too much gap, which can cause a loud, deep knocking sound.
3. Bending. Extreme stress or heat can bend the shaft. This wears the bearings unevenly and causes vibration. The journals may need machining, or the whole part may need to be replaced.
4. Damaged sensor or sensor ring. A bad crankshaft position sensor can throw off engine timing, leading to rough running or stalling. On some engines the sensor ring is part of the crankshaft itself, which makes repairs harder.
How it is fixed
There are not many quick fixes for a damaged crankshaft.
1. Inspection and machining. For minor damage, a machinist can grind the journals slightly smaller, as long as the hardened outer layer is not ground away too much.
2. Replacement. This is the most common and reliable fix. The old crankshaft is swapped for a new or rebuilt one, along with matching undersized bearings. It is often the most affordable option too.
3. Advanced rebuilding. For costly or hard to find crankshafts, shops can build up worn surfaces with metal spraying or laser cladding. This takes special equipment and careful quality checks to get the hardness and strength right.
How to prevent problems
1. Change your oil on time. Clean oil keeps a thin protective film between the crankshaft and bearings. This is the most important thing you can do.
2. Fix oil leaks quickly. A leak can leave the engine short of oil and cause fast, serious damage. Leaks from the front and rear main seals can also harm the crankshaft surface.
3. Do not ignore strange noises. A deep knock when you speed up, or unusual shaking, is often the first sign of a crankshaft or bearing problem. Get it checked right away.
