Date: 11 May 2020

The different types of crankshafts

Crankshafts are one of the most crucial parts of internal combustion engines and are made to withstand extremely heavy loads during engine use. There are several different types of crankshafts, including:

Fully built

Fully built crankshafts are made of components that are shrink-fitted after being fabricated separately. Fully built crankshafts can be found on most older engines, in which crankpins, main journals and webs are forged individually. After the journals and crankpins are created, matching holes are bored within the webs. These webs are then heated up and the journals and crankpins are slotted into the holes which expand in size due to the heat. As the webs proceed to cool down, the holes begin to shrink, gripping the journals and crankpins in place to prevent them from slipping as the engine is operated.


For welded crankshafts, each element is made of webs with crankpins and half of the main journal on either side. The number of forgings are calculated based on the size of the unit and are then welded together using the submerged arc welding technique. The forgings are then stress relieved and connected together to create the crankshaft. Welded crankshafts have the benefit of a continuous grain flow, which allows the webs to be made thinner which can create a shorter and more lightweight crankshaft. However, welded crankshafts are more expensive to manufacture and so only a few of them have been used successfully.

Semi built

With semi built crankshafts, elements such as the pins and crank-throw are created out of a single forging. The crankshafts of large two-stroke crosshead engines are usually semi built. The advantage of semi built crankshafts is that by creating the crankpin and two webs from a single forging, the steel's grain flow follows the web all the way around through the crankpin and down to the other web. The webs can be made thinner than in conventional methods and a hole is drilled through the crankpin, which makes the crankshaft more lightweight without reducing its strength.

If you're in need of a specialist on-site machining service, crankshaft repair service or line boring services, get in touch with our friendly team at In-Situ Machining Solutions by giving us a call on +44 (0)1788 572777 or by dropping us an email at [email protected].

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