What is Crankshaft: Definition and 29 Discussions

A crankshaft is a shaft driven by a crank mechanism, consisting of a series of cranks and crankpins to which the connecting rods of an engine is attached. It is a mechanical part able to perform a conversion between reciprocating motion and rotational motion. In a reciprocating engine, it translates reciprocating motion of the piston into rotational motion, whereas in a reciprocating compressor, it converts the rotational motion into reciprocating motion. In order to do the conversion between two motions, the crankshaft has "crank throws" or "crankpins", additional bearing surfaces whose axis is offset from that of the crank, to which the "big ends" of the connecting rods from each cylinder attach.
It is typically connected to a flywheel to reduce the pulsation characteristic of the four-stroke cycle, and sometimes a torsional or vibrational damper at the opposite end, to reduce the torsional vibrations often caused along the length of the crankshaft by the cylinders farthest from the output end acting on the torsional elasticity of the metal.

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  1. paradisePhysicist

    Building a better crankshaft (crank and slider)

    I am trying to build a dual input (double input) crankshaft, out of Lego. All the tutorials online use flywheels, but I want a strong high quality crankshaft that doesn't rely on flywheels. The crankshaft is for a 1 cylinder or sinusoidal linear type input. This video demonstrates the flaw of...
  2. V

    Automotive The reason for the low efficiency of the ICE - zero shoulder crankshaft

    I don't know English well, translated using google translate. The working mixture ignites at TDC, and at this point the crankshaft looks up (0 degrees). As the piston descends, the force that the piston needs to travel a certain distance (for example, 1 mm) decreases, up to the moment when the...
  3. nick26

    Measure angular velocity and acceleration from missing tooth wheel

    Hi, I need to come up with a math model for a digital ignition system. I've been thinking about it and I think that I need to measure 2 things to be able to calculate when I have to start charging the coil. They are the angular velocity and the acceleration but how can I do it? the idea is to...
  4. Y

    Why is Point A in Compression in a Simplified Crankshaft with a Load P?

    Summary:: I'm stuck on a year 2 mechanics question. I have this simplified crankshaft with a load P at the end. The solutions to the exercise have said that point A is in compression due to a bending moment but I don't understand why that is. The solutions and my calculations have both come out...

    Trying to find the torque required to turn the crankshaft in my mechanism

    Hello!, First post and I am excited. I am an artist and want to see if the motor I have selected for this mechanism will work for a project I am working on. I am trying to see if the gearbox/motor I have sourced for this mechanism is powerful enough to drive it. The weight of the object I...
  6. raclemai

    I need to maximize my RPMs in a single cylinder flywheel

    I am working on a flywheel single-cylinder engine powered by a 40 psi air compressor. My task is to achieve as many RPMs as I can. I have already bored two exhaust ports in the frame as shown in the pictures attached. I've done some 600grit sanding on points of contact, am using lubricant prior...
  7. Matthew Titus

    Calculating Motor Torque for Cricket Bat Knocking Machine

    Homework Statement Good day, i am currently working on a design project. the device is part of a cricket bat knocking machine. i need advice on how i would go about calculating the motor torque required Homework Equations Tq = Inertia x angular acceleration The Attempt at a Solution attached...
  8. I

    Calculating the forces on a crankshaft assembly

    Hi everyone, So I'm working on this project where I have to determine the total force that is being applied to an assembly that is attached to a crank shaft which is in turn attached to a motor that's driving it. I looked up the equations for the acceleration and velocity of a crank shaft (or a...
  9. A

    Piston with crankshaft: what is the temperature of gas entering the cylinder?

    Homework Statement Homework EquationsThe Attempt at a Solution e) I know the temperature is lower in the transparent container but how do you represent this
  10. person123

    B Confusion About Oscillating Mass

    I'm sure there's an obvious answer to this, but this problem has been confusing me for some time. Imagine there were a massive object attached to the end of a crankshaft. A force is applied to accelerate the crankshaft, causing the mass to oscillate. Assuming there is no friction, what would...
  11. ramzerimar

    Dynamics problem: Crankshaft angular speed?

    Homework Statement Homework Equations Kinematic theorems: The Attempt at a Solution Ok, I'm trying to use another angle, phi, and find some relation betwen phi and theta so I can derive the equation for the angular velocity of rod B with respect to S, but I'm stuck at that point. How...
  12. Prasad birari

    Automotive One piece or multi piece crankshaft

    Just curious to know what difference does it make while using multi piece crankshaft instead of single piece crankshaft?
  13. F

    Design Your Own 50ci Engine: Balancing Crankshaft

    Hi, I am going to design my own 50 ci engine, straight 4 cylinder 2 stroke. I know nothing about how I should go about the crankshaft... Very few drawings so far, can anyone guide me on any formulas i should use to figure out what i need, based on piston weight, rod weight and size, etc...
  14. A

    How to calculate angular acceleration of crankshaft?

    Hello. I am currently undergoing a university project and require the angular acceleration of a crankshaft? I only know the angular velocity from the RPM and I have strongly considered that it is not possible. Just looking for some reassurance? Cheers
  15. W

    Do I Need a Counterweight for My Crankshaft?

    I have a crank shaft that lifts a flatplatform up 0.5 inches and down 0.5 inches. The load here is about 250 lbs. So just one load on this 3" long steel shaft with 1 inch thickness. Is it necessary to have a counter weight for this? If so, how much should the counterweight weight? The shaft...
  16. C

    Drilled crankshaft, Honda Africa twin

    Hello everyone! I'm new here, I'm italian, so please forgive me for my bad english. So, here the situation.. i'm a owner of a Honda Africa twin, which unfortunately has the crank shaft( where the pinion has to be inserted ) that has the teeth a bit worn. So i opted for a modify : I drilled the...
  17. E

    Questions to do with crankshaft of an engine

    Homework Statement A cylinder in a truck engine are shown in Figure Q8.1 below. The piston slides without friction in the cylinder of diameter 150 mm. The combustion chamber is subjected to an internal pressure of 50 bar gauge as a result of fuel combustion without any leakage past the piston...
  18. R

    Speed Torque characterstics of Crankshaft

    Hi all, I want to know reason behind the variation of torque with respect to the rpm of the engine. I understood that the torque would decrease as the engine rpm increases.But, When i look into the characterstics graph of speed vs torque of the crank shaft engine(Graph is attached),It...
  19. S

    Crankshaft Balance: Is a 45° Angle Possible for a V8?

    So for the last 3 years (off and on) I have been designing an engine. I have gotten much more serious lately as it could help me get a job that I seriously want, but somethings have stopped me in my tracks. On of the biggest things is the g.d. crankshaft. It is a pain because it does so much for...
  20. Baluncore

    Automotive Crankshaft axis offset from cylinder axis?

    I have always thought of connecting rods as straight and the crankshaft axis being line bored in the same plane as the cylinder axis. Is there an advantage in offsetting the crankshaft slightly to compensate for the difference between the compression and power stroke pressures ? Is the answer...
  21. Y

    How to Redesign a Crankshaft for Dual Connecting Rods?

    I am redesigning a crankshaft to support two connecting rods per journal from it's stock one per journal. I will be machining a new crankshaft out of 4340 billet. This design will reduce the counterweights to 9mm in thickness. This engine is a 9k redline design so I need to get this right. Can...
  22. B

    How to calculate force needed to push piston based on crankshaft value

    Homework Statement How do you calculate the force needed to push against a piston based on the mass of the vehicle, the rpm of the crankshaft, radius of crankshaft (same distance as the center of the crankshaft to the attachment point of the connecting rod and the crankshaft), and the length...
  23. M

    Calculating the force on a Crankshaft in a Steam Engine

    Given that I have a steam engine, and now its size, the size of the piston, the length of its stroke and the force acting on the piston at certain points, I need to calculate the force on the crankshaft. Now, I now that Fx should be the same where the piston meets the crank, and we can ignore...
  24. P

    Crankshaft Failure Mode Analysis

    I have a broken crankshaft where I am trying to determine the cause of failure. here are some pics of the cracked surface. what is known: 1) the crank shaft was under very light load at time of failure What do you guys think?
  25. I

    Piston stroke length based on crankshaft degree

    I am wanting to form an equation I can use on excel that allows me to find how far the piston has gone down depending on how many degrees the crankshaft has turned. I know the length of the stroke but I also know that the stroke is not linear to the degrees turned, as in the stroke goes farther...
  26. Ranger Mike

    Is Offset Grinding the Key to Increasing Engine Power?

    Grinding the crankshaft is a relatively straight-forward process. The crankshaft nose is placed into the head stock chuck and the crankshaft flange (in some cases the crankshaft seal surface) is secured in the tail stock chuck. At which point the main journals can be ground. The rod journals are...
  27. C

    Crankshaft Lubrication in IC Engines: Questions Answered

    as i have seen, usually in ic engines, the oil is forced into the journal bearings and then it travels along passages in the shaft to connecting rod bearings. but how, does it enter the passages in main bearings with so much centrifugal force. if i understand correctly, the cetrifugal force is...
  28. R

    Can a Car's Engine Rotate in Reverse at Startup?

    Hi guys Let a single cylinder ic engine. Now when we start the engine , then depending upon the position of crank the last time we switched off the engine, it is possible it may rotate in reverse direction because piston just has to reciprocate so acco to crank position at rest it may move...