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I have heard that use of counterweights in crankshafts also help with bearing life because "counterweights reduce peak main bearing inertia loads". Is this true? If its true how does that exactly help reduce the loads on the bearing, i couldnt quite understand it.

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Yes, because the counterweights are there to reduce or elimination of vibration.

If you consider the vibration is caused by a movement of the crank against the bearing then it can be considered it is causing damage.

Engineers calculate the offset rotating loads for the rotation of the crank and design the counterweights accordingly.

Then if the power strokes overlap then the engine feels smooth: consider a v8 or v12 compared to a 4 cylinder. Of course a 4 cylinder can have a heavy flywheel to help this.

An inline 6 is known as a smooth engine as it is in balance for primary forces.

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  • I understand that they reduce vibrations etc and therefore the load on the bearings but for example early 911 crankshafts had no counterweights, it didnt need them because boxer 6 has great primary and secondary balance and the conrods cancel each other out as well.So there wasnt really any need for counterweights as far as engine balance goes (from what i understand) But later porsche introduced counterweights to the cranks to "reduce the load on the bearings and make them last longer". Thats what i read about why they introduced them and i wondered how exactly that will reduce bearing loads. Apr 21 at 15:27
  • @TimothyScherer well, looks like I answered your original question so now you are changing the goal posts. Not playing that game.
    – Solar Mike
    Apr 21 at 15:36
  • Thats what i tried to ask with my original question but i tried to keep it as short as possible so maybe there was a misunderstanding due to that. I probably should have worded it better in my first post, my bad. Also i didnt understand what you mean by game im not trying to trick you or something. Apr 21 at 15:55
  • Even if an engine is well-balanced overall, it’s beneficial for the crank to be balanced for each piston, otherwise it will tend to flex (albeit only a tiny amount) which will transfer force onto the crankcase. In a perfectly balanced engine the main bearings would only support the weight of the crankshaft, but crank flex could lead to much larger forces.
    – Frog
    May 22 at 6:23

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