Difference between "Inline Twin" and "Parallel Twin"?

[sadsack]

I made a mistake in my previous post. In the third line of the first paragraph it should read "movement of pistons" instead of "movement of cylinders". Please excuse me.

[mansuryayas]

You know Aargee you are very clear in what you are saying, and I am very sure that it would be very difficult to build a Parallel 4 Cylinder engine but Inlines can have any configuration.

Parallel twins are known as such due to their inherent Twin Nature to work in sync, 1up both up, 1 down both down, they may fire are different cycles but they are different from inlines

[sadsack]

This is an old thread that seems to have been revived again. I do not know if I am doing the right thing by prolonging this again. Since the motorcycle under discussion here has been the Kawasaki Ninja 250R and since I own one, I had actually asked the mechanic about the piston movement. Fortunately he was working on an engine that had been stripped and one could clear see the piston inside the cylinders. They do not move up and down together, I saw this for myself. It is also not as simple as one is going up and the other is going down. They do not move together but where the position of one piston is relative to the other is difficult to tell since the mechanic also did not know the angles on the crankshaft and the firing intervals. The works manager was also very clear that "parallel" indicates the placement of cylinders and not movement of pistons. You can have longitudinally placed parallel twins or transversely placed parallel twins, the second being almost the norm since it helps more compact packing of the engine in the frame. The same explanation is true for inline as well. I was told by the works manager that in the case of twins the "convention" is to use the term twins while in more than two cylinders the "convention" is to use inline. For example in inline four engines you can have the screamer engines that have an even firing order facilitated by a certain angle on the crankshaft (do not know the exact angle, so not mentioning) and these engines have a tendency to "wail" or " scream" (and hence the name screamer) and these engines are known to be very hard on tyres. The other configuration which is the "growler" or big bang is due to a cross plane crankshaft (again I do not know the exact angle) but here the firing order is not even and therefore the engine sounds as if it is a bit out of tune at low revs and also produces "gruff growling sounds". This configuration is less harsh on the tyres and gives the rider better throttle control. However what is important here is that in the "growler" inline configuration due to the cross plane crankshaft the movement of pistons is not as if the firing within cylinders happens in sequence from 1 to 4. The geometries will dictate the order of how the cylinders fire. It can be 1 and 4 and 2 and 3 and more such combinations. This is a layman's explanation, I am not a techie but parallel twin does not denote the parallel movements of pistons.

[icemang]

What I am posting below agrees in toto with what I was taught at various places by various people. This explanation should set to rest the issue. The differences between the two are amply given by the red font.

Credits and courtesy Wikipedia

A straight-two engine, (aka straight twin, parallel twin, inline twin, or vertical twin) is a two-cylinder piston engine that has its cylinders arranged side by side.



The motorcycle world generally refers to these engines as "parallel twins" or "vertical twins", and the term "straight-two" is obsolete. "Parallel twin" refers to an engine mounted transversely across the frame; and the term "inline twin" refers exclusively to an engine mounted inline with the frame, such as the Sunbeam S7. In four-stroke designs, the parallel twin is usually vertical or near vertical. An exception is the racing-only AJS Porcupine, which featured nearly horizontal cylinders, and Suzuki two-stroke, small bore, street-bikes.

[Da1AnOnlyHermit]

I think they are the same. As far as i can remember its the same layout with different names. I'll try to dig out the book I read a long time back!

And as far as the cheetah goes at 'max revs' its 1 an 2 then 3 an 4 that is their 'sprint cycle'

The elephants on the other hand always do 1,3 and 2,4 all through their 'rev' band.

[aargee]

Yes, they're the same

[Berlin]

Originally Posted by aargee

Yes, they're the same

a very good thread.

so the parallel twin and inline twin are the same with different names?

i read the thread from top to bottom, but i couldnt understand some posts, because i am technically not up to mark...

[aargee]

Originally Posted by Berlin

so the parallel twin and inline twin are the same with different names?

Yes they are; if my previous posts are confusing, that was when I started.

[psr]

I hope the links below helps in understanding the engine configurations...

Motorcycle engine - Wikipedia, the free encyclopedia

http://en.wikipedia.org/wiki/Straight-two_engine