Why inline-4 engines needs counterweights?
Why inline-4 engines needs counterweights?
(OP)
Hello, if in inline-4 engines primary forces are balanced (1-st and 4-th cylinder balances 2-nd and 3-rd cylinder) then why does it need counterweights on crankshaft?





RE: Why inline-4 engines needs counterweights?
The crankshaft may be a big chunk of steel ... but it can and does want to flex and bend, constrained by the main bearings.
RE: Why inline-4 engines needs counterweights?
Piston speed is not sinusoidal, which means they are at different speeds throughout different portions of the stroke.
While 2 pistons are at TDC, the other two are at BDC. The pistons change direction faster at TDC than they do at BDC.
That creates excitations and secondary imbalance. This is why you rarely see a high revving 4 cylinder, or any other flat-plane crank engine having large displacement. My boat has a 3.5L 4 cylinder, but that uses a cross-plane crank with all the counterweights you could want!
"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin
RE: Why inline-4 engines needs counterweights?
RE: Why inline-4 engines needs counterweights?
"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin
RE: Why inline-4 engines needs counterweights?
Cheers
Greg Locock
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RE: Why inline-4 engines needs counterweights?
We need to get on the same page before this turns into a nerd fight.
"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin
RE: Why inline-4 engines needs counterweights?
RE: Why inline-4 engines needs counterweights?
"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin