Intellectual engine questionnnnn...

[slammin.e28]

So, piston driven internal combustion engine.

The question:

The piston, at TDC or BDC, we can all agree it reverses direction, from up to down, or from down to up, right?

Now, in the reversing of that direction, does the piston STOP, then go the opposite direction.

Or by some black magic does it continue in motion in some uncanny oblong circle?






Or, aliens?

[travish325]

Yes it stops, if only for a millionth of a second, But other pistons are at different points so you wont notice it.

Can you go in reverse in your car while driving foward without stopping first?

[slammin.e28]

I have heard arguments for it continuing in motion, from engine builders, etc.

I'm like whuut?

[Wh33lhop]

Theoretically it stops, in practice it will tilt a little bit at the top/bottom of the stroke. It "remains in motion" because it's connected to the crank that remains in motion and it can only be stopped for an instant. But the piston itself stops.

[AndrewBird]

Well, it doesn't pause if that is what you are asking. It is at the top (or bottom) of the stroke the same amount of time it is in every other position throughout its stroke. While it might seem like it is stopping, it is still technically moving, just to a very small degree.

Edit: To add further, it stops going one direction then instantly moves in the opposite, with no gap in time, No pause like I referred to earlier.

[LJ851]

I've built a lot of engines and i think it stops. When you are finding absolute TDC when degreeing cams you can watch it stall momentarily, the crank turns and the dial indicator (on the piston) remains fixed. This is one of advantages of long rods, it increases the dwell time at TDC.

[Wh33lhop]

Well, it doesn't pause if that is what you are asking. It is at the top (or bottom) of the stroke the same amount of time it is in every other position throughout its stroke. While it might seem like it is stopping, it is still technically moving, just to a very small degree.

Edit: To add further, it stops going one direction then instantly moves in the opposite, with no gap in time, No pause like I referred to earlier.

If you are defining "stopping" to have zero vertical velocity then it stops. Just not for any period of time.

[F34R]

I always believed the piston came to a hanging point that was cycled by the other pistons in motion.

[LJ851]

I always believed the piston came to a hanging point that was cycled by the other pistons in motion.

How does that apply to single cylinder engines?

[gtdragon980]

Shit, I got confused by the way you meant reverses direction. Now I get it. In that case, I voted wrong, I would say it stops for a fraction of a second, since the rod has to move from one side to the other, which then it pivots underneath before the crank begins to pull it back down.

[reelizmpro]

Well if you run in a given direction, you don't just reverse in the opposite direction without stopping momentarily. In the case of the piston, they may be including the circular swing of the force on the piston but the piston is kept pretty straight by the cylinder walls/rings with only a very very small gap in between but it still has to "stop" momentarily.

[ADlBOO]

How does that apply to single cylinder engines?

Single cylinder engines have counter weighted crank shafts that provide the momentum.

[F34R]

How does that apply to single cylinder engines?

Momentum created from combustion continues rotation is my best guess. So with the other pistons in multi cylinder engines it allows more hp generated from more pistons forcing rotation?

My best thought out logical response...

[LJ851]

Single cylinder engines have counter weighted crank shafts that provide the momentum.

Thats what flywheels are for.

The counter weighted cranks (on all engines that need them) is to achieve a balance factor for smooth running in a given rpm range.

[slammin.e28]

Okay, for clarification, let's say it's an M30 (tee hee). Multiple cylinders.