The crankshaft is the main rotating shaft that turns the up-and-down motion of the pistons into the spinning power that drives the wheels. It is the backbone of the engine's lower end.
Animated: how a Crankshaft actually works
🔧 How It Works, Step by Step
1
Receive piston force
Each connecting rod pushes on an offset section of the crankshaft called a crank throw.
2
Convert to rotation
The offset throws let the downward push of the pistons spin the shaft, like pedals turning a bicycle crank.
3
Ride on bearings
The crankshaft spins on oil-cushioned main bearings that keep it centered and friction low.
4
Send out power
One end drives the flywheel and transmission while the other drives the timing gear, belt, and accessories.
🧩 The Key Parts
Main journals
The polished sections that ride in the main bearings and hold the shaft in the block.
Rod journals
Offset surfaces where the connecting rods attach and apply force.
Counterweights
Balance the spinning assembly so the engine runs smoothly.
Reluctor ring
A toothed wheel the crankshaft position sensor reads to track engine speed and position.
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The 50 most common check engine codes with likely cause and DIY fix cost. Sent once.
🩺 Signs of a Failing Crankshaft
Deep knocking from the bottom of the engine
No-start or stalling from a sensor fault
Vibration that grows with engine speed
Low oil pressure warning
Metal flakes in the engine oil
⚠️ Common Problems
Spun or worn bearing
Oil starvation or high mileage wears the main and rod bearings, causing a deep knock and eventual crankshaft damage.
Crankshaft position sensor failure
A failed sensor leaves the computer blind to engine position, causing hard starts, stalling, or a no-start condition.
Cracked or bent crankshaft
Severe detonation, a seized bearing, or an over-rev can crack or bend the shaft, requiring a rebuild.
💰 Cost to Fix
$200-$4,000typical range to repair or replace, parts and labor
❓ FAQ
What does the crankshaft do?
It converts the straight-line motion of the pistons into the rotating motion that turns the flywheel, transmission, and ultimately the wheels.
How much to replace a crankshaft position sensor?
Most crankshaft position sensor jobs run $200 to $500 including parts and labor, far cheaper than replacing the shaft itself.
Can a crankshaft be repaired?
A machine shop can polish or regrind worn journals and fit oversized bearings, but a cracked or badly bent crankshaft must be replaced.