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

[aargee]

If you can give any other proof that says so, I'll eat my words.

No, you don'tve to take back your words as we're not even debating or arguing here; we're just sharing our knowledge here.

But I thought the Youtube was well more explained than anything. Are you saying that's insufficient?

[iamvik]

Just to jump into this pond:

Parallel twin: engine with 2 cylinders whose axes are parallel.
In-line twin: engine with 2 cylinders that are placed parallely next to each other.

The crankshaft configuration and cylinder firing order have no relation to the names parallel twin or in-line twin.

E.g. A V-twin is a V-twin, whether it's called a V-twin, like most manufacturers do or an L-twin, as Ducati does. It is just a different name that's all.

[aargee]

Last night I'd a little time in train other than reading & was thinking about this parallel & inline twins (no wifey to bug ).

Parallel twin - I hope this setup can be made only with a maximum of twin cylinders unless the engine needs a double firing on two-two cylinders at the same time. Idea being on a 4 cylinder configuration, with all 4 cylinders at top, with 2 cylinders firing at 180 & other two at 360. Pls let me know if this is not clear, I can explain further.
Inline twin - Does not have any such limitation & can have 2,3,4,5,6,8 cylinder configuration with 360, 240, 180, 144, 120 & 90 degree firing. (7 gave me a odd figure of 102.8 & thought it would be difficult to construct)

So, experts, is my assumption above right or wrong? Pls don't let this thread to sunset & share your knowledge with me pls.

[aargee]

I was just thinking about the Cheetah, Horse, Wolf & a Deer & observing their running pattern. Here're my observation

Cheetah - Puts RHS front leg, LHS front leg, LHS back leg & finally RHS back leg & at any point in time, there's only one leg on the ground.
Horse - Puts RHS front leg & RHS back leg, LHS front leg & LHS back leg & at any point in time, there're two legs on the ground either from left or at right
Wolf - Puts RHS front leg & RHS back leg, LHS front leg & LHS back leg & at any point in time, there're two legs on the ground either from left or at right
Deer - Puts RHS front leg & LHS front leg, RHS back leg & LHS back leg & at any point in time, there're two legs on the ground either from front or at back

So what're these doing on a parallel & inline twin engines? Before the mods could delete my ridiculous post, let me convey what I'm trying to say.

Look at the pattern of Cheetah, it just goes like firing on cylinder 1,2,3,4 or 1,3,2,4 like an inline, the firing is spread out & hence the tremendous power & the body weight of Cheetah is less to support the weight on one leg at a time.

Look at all other animals, the firing pattern is 1-2-1-2 like a parallel, at any point the firing is only on two & irrespective of the body weight the speed still prevails.

PS - Something seriously wrong with my brains these days!!!

[aargee]

Adding another thought...
On a 4 stroke engine - A Parallel twin engine can be constructed only with two cylinders & an inline engine can be constructed only when there're more than two cylinders.

On a 2 stroke engine - I'm not even sure if a parallel twin exists or there can be an engine with more than 2 cylinders. Even if one can be made with more than 2 cylinders, then its inline.

Appreciate for any pointers.

PS - No wonder I couldn't get a video on an inline engine for a 2 cylinder.

[iamvik]

I don't understand your confusion. Saying a parallel twin can only be 2 cylinders is obvious since you've added the word twin! Inline and parallel are the same thing; I don't understand why you seem to think they are not such. If you want, you could call an in-line 4 cylinder as a parallel four cylinder. It's all just semantics.

The RD350 is a 2 stroke parallel twin. Kawasaki used to make parallel 3 and 4 cylinder 2 stroke bikes upto 750 cc. Don't remember the names, though.

Animals walk and run with different gaits. At no point will their body weight be supported by only one leg since that would be unstable. Comparing animal gaits to engine firing orders is weird and I don't see any value in it. For you to understand firing orders you would have to be familiar with mechanics and particularly kinematics and dynamics of machines.

[aargee]

I don't understand your confusion.

I've no confusions

Saying a parallel twin can only be 2 cylinders is obvious since you've added the word twin! Inline and parallel are the same thing;

No; you need to go through previous pages to understand; look at the videos & then come back pls.

The RD350 is a 2 stroke parallel twin.

LOL; pls check & get back as I've checked its inline.

Kawasaki used to make parallel 3 and 4 cylinder 2 stroke bikes upto 750 cc. Don't remember the names, though.

Again, pls check & let me know, I would like to learn more if you can get me the models.

Animals walk and run with different gaits.

Right, but no animal can change its running/walking position. Imagine you run with both your hands & legs & I'm sure you'll be unable even to walk.

At no point will their body weight be supported by only one leg since that would be unstable. Comparing animal gaits to engine firing orders is weird and I don't see any value in it. For you to understand firing orders you would have to be familiar with mechanics and particularly kinematics and dynamics of machines.

Pal, do you want a debate or an argument here? Pls try to understand & then come back for a healthy debate; I'm only posting my thoughts here just by mere observation, it could be wrong, but if you disagree you've to prove me wrong. I've clearly explained the engine firing & animal's movements in my post. If you're unable to understand, pls let me know what you haven't understand before concluding it doesn't have a value in it.

PS - Animals have taught human invariably many things. 2 Years back I came across an article that was stating that automotive engineers are working along with biologist/veterinary (could be wrong on the terms) to understand the animals to incorporate their structurals.

EDIT - The pic of RD350 crankshaft is given here - http://www.froggy.se/skalmanmc/rd350...rank/index.htm
If you look the pics carefully, you can observe that when one of the piston goes up the other comes down; if it were parallel, then both would be up or down at any point in time.

[iamvik]

I've no confusions


No; you need to go through previous pages to understand; look at the videos & then come back pls.


LOL; pls check & get back as I've checked its inline.


Again, pls check & let me know, I would like to learn more if you can get me the models.


Right, but no animal can change its running/walking position. Imagine you run with both your hands & legs & I'm sure you'll be unable even to walk.


Pal, do you want a debate or an argument here? Pls try to understand & then come back for a healthy debate; I'm only posting my thoughts here just by mere observation, it could be wrong, but if you disagree you've to prove me wrong. I've clearly explained the engine firing & animal's movements in my post. If you're unable to understand, pls let me know what you haven't understand before concluding it doesn't have a value in it.

PS - Animals have taught human invariably many things. 2 Years back I came across an article that was stating that automotive engineers are working along with biologist/veterinary (could be wrong on the terms) to understand the animals to incorporate their structurals.

EDIT - The pic of RD350 crankshaft is given here - Yamaha RD 350 crankpage
If you look the pics carefully, you can observe that when one of the piston goes up the other comes down; if it were parallel, then both would be up or down at any point in time.

Whether or not pistons are moving in phase or not, cylinder axes are parrallel, crankshaft pin axes are parallel, connecting rod planes are parallel. So why wouldn't an RD engine be considered and called as parallel? What makes it non-parallel geometrically?

I agree that we can learn a great deal from observing animals but it's all based on context. It's not that I don't understand your post about animals gaits but the context is completely different from engines. I think comparing animal gaits with engines would only be in the same context if an engine had four cylinders arranged parallely but as a square, with each cylinder being one corner. This would experience balance issues similar to quadruped animals.

Look for yourself at dogs, the most common animal in cities. The way they walk is different from the way they run. It is easy to observe that while walking they pair diagonally opposite legs and while running they pair adjacent legs. The transiition gait between walking and running seems to be a mix of the two.

If you make an argument or observation and someone disagrees with that, it does not oblige them to prove you wrong since your argument may not be wrong to begin with. It could be that what they state is more true than what you state. Since all the statements so far in this thread have been rational and civil, why do you assume that once somebody disagrees with you it becomes a fight?

[aargee]

Whether or not pistons are moving in phase or not, cylinder axes are parrallel, crankshaft pin axes are parallel, connecting rod planes are parallel. So why wouldn't an RD engine be considered and called as parallel? What makes it non-parallel geometrically?

Pal, why don't you, for once, watch the videos posted on page 2/3 on parallel twin & inline, understand them and then come back to debate? I know you're desparate to prove me wrong, which I sincerely like to otherwise I would be always in the wrong notation, but pls talk with respect to context is my request.

Look for yourself at dogs, the most common animal in cities.

Dogs are well known for faithful animals, but not the fastest animal (Cheetah) or used for riding (Horse), so appreciate if you can take a right example to debate.
PS - I've already taken a dog family - The Wolf.

[sadsack]

I would like to add something here. But first a disclaimer. I am not a techie and after following this discussion I have consulted someone who claims to be in the know of things. As per that person, parallel and inline can both be used to denote cylinders that are placed side by side and have little to do with the firing order or the movement of cylinders. In technical terms one has to say "parallel (or inline) twin with so and so firing order".

It is not really possible to conclude anything from the You Tube video since one is showing a twin cylinder and the other a four cylinder. The depiction of the four cylinder seems to that of an uneven firing order and a cross plane crank shaft leading to pistons 1 and 4 and 2 and 3 moving almost together. This cannot be conclusive evidence to differentiate between a parallel twin and an inline twin.

The Wikipedia article should be taken with a pinch of salt, since we are not aware of the expertise of the person who posted that information there.

[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.