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KnifeEdge_2K1
09-03-2004, 10:04 AM
while we're on the subject of engines maybe we should discuss the harmonics of each type of engine like why 3 cylinder engines need a balancer shaft while a 4 cylinder needs twin ballencers while 6 cylinders dont need em at all

i understand it but cant explain it

basically the 3 cylinder will jump up and down because of how the crankshaft and pistons are aranged while a 6 cylinder doesnt because its just two 3 cylinders glued end to end cancelling out each others up down movement

as for twin ballencer shafts in the 4 cylinder engine its gonna take a while

as you may imagine a 4 cylinder inline engine will be comepletly ballenced for the first order force
imagine this

1234
- -
--

this is basically the layout of all inline 4 cylinders

the group 1,2 ballence each other while the group 3,4 ballence each other

the problem is however when piston 1 is at the very top of its movement of the crank shaft piston 2 would be at the bottom but moving slower due to the geometry of the engine
the slower velocity will cause the displacement ratio (sorry i cant put it in better terms) to change causing vibration
this same thing also happens to 3 cylinders (i think) but since most 3 cylinders are low in displacement this effect is minor while in 4 cylinders its more pronounced since they usually have larger displacement, its generally agreed that all 4 cylinders with 2 litres of displacement or more need twin ballencer shafts to operate smoothly and efficiently

ive drawn up a picture to explain this but its kinda hard to understand

KnifeEdge_2K1
09-03-2004, 10:19 AM
there

Matra et Alpine
09-03-2004, 05:59 PM
Not all V6s are 'smooth' runners and some do need balancing.

In fact, some 4s need balancing, but not usually in cars.

The part missing is the assumptions made about firing order and the rotational offset between each firing combusion chamber.

I'll try and find some stuff I have on it, cos balancing gets difficult to describe when we talk about firing order and crankshaft angles :(

But ANOTHER good topic for UCP, KE, and why I've pulled it into it's own thread.

KnifeEdge_2K1
09-03-2004, 08:19 PM
i meant strait 6 :D