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What is a crankshaft and what does it do?

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Updated 9 Oct 2019Jason Unrau
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Of all an engine’s moving parts, the crankshaft is the biggest and heaviest.

There’s no doubt about it, the crankshaft is the foundation on which the combustion engine is built.

No part of the process – intake, compression, combustion, or exhaust – occurs without a crankshaft to put it into motion.

But for most people, understanding how the crankshaft operates isn’t quite clear.

Here’s how it works, what its purpose is, and what can go wrong with the crankshaft.

What is the Crankshaft?

The name ‘crankshaft’ goes back to the early 20th century when car engines were started with a crank handle, and cranking it over was literally rotating the crankshaft with a hand crank.

Today, electric starter motors do that job, but the internal component is still called a crankshaft.

The crankshaft rotates inside the engine but is held firmly in one location at the main bearing journals.

Then, the pistons that move up and down in the cylinders are attached with connecting rods to the rod bearing journals.

The rod bearing journals are staggered strategically, moving the pistons in a rhythm that balances the engine’s mass while in motion.

Keep in mind that the crankshaft has to be extremely strong – it rotates hundreds or thousands of times per minute!

But that’s not where the crankshaft’s job ends.

A sprocket on the front of the crankshaft times it in sync with the camshaft.

These parts function in tandem for the engine to run smoothly.

How Do I Know if There’s a Problem with the Crankshaft?

Lubrication is incredibly important for the crankshaft to stay in good condition.

So, if engine oil changes aren’t performed routinely, it can cause wear and tear on the crankshaft, or cause it to fail.

Crankshaft problems aren’t usually subtle. They include:

  • Engine knocking due to excessive wear on crankshaft main journal and rod bearings
  • Low oil pressure readings from sloppy tolerances
  • An engine that won’t start due to being seized

Can the Crankshaft Be Repaired?

A failed crankshaft is a major undertaking, and even minor damage to the crankshaft can yield major problems.

In some cases, gouges or scratches in the journals can be resurfaced and larger bearings installed, compensating for the material removed from the crankshaft.

If the damage can’t be corrected completely, a new crankshaft will need to be installed or you risk another failure soon after.

How Much Does Crankshaft Replacement Cost?

As mentioned, crankshaft replacement is always a major repair.

It’s part and parcel with an engine rebuild in most cases.

For most vehicles, the crankshaft as an individual component is between $400 and $800.

However, it’s more than a full day’s labour for an experienced mechanic to change the crankshaft, plus there are gaskets, fluids, and other minor parts that will be required.

On average, you can expect crankshaft replacement to cost between $2,000 and $2,800 for most models.

If you’re in need of a crankshaft replacement, it’s a good idea to get a qualified mechanic to do the job to ensure it’s done correctly.

You can use AutoGuru to search and compare local, high-quality mechanics to get your crankshaft replacement booked in.

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Written ByJason Unrau

Jason is a Canadian automotive content writer with a background in the auto service industry, but he’s been hooked on cars and mechanics since childhood.

One of his first cars was an ’80 Mazda RX-7 that’s sorely missed to this day. A ’68 Ford Torino GT, a ’66 Ford Country Squire Woodie station wagon, and a ’96 Suzuki GSX-R 750 have spent time in his fleet of cars, bikes, and trucks over the past two decades.

Jason’s pride and joy is under construction – a turbocharged ’88 Mazda RX-7 convertible. Also on his resume is CASCAR official certification.