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Discussion Starter #1
I'm sitting in the airport waiting for my flight and I'm thinking about motorcycles. I'm wondering -- what are the pros and cons of the various engine configurations: V vs. flat vs. inline. Is it simply a matter of the space the engine takes up? Is one design simpler than another?

I'm not an engineer, but it seems to me with these kinds of things there's always a series of trade-offs being made. What would those trade-offs be?

No reason for this question ... just curious.
 

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I'm posting my opinions here, and others will likely have more to add, or point out that I'm wrong in places. In my experience, horizontally opposed engines (BWM, VW Beetle (old one) Subaru, small aircraft engines) are the best balanced and smoothest engines that you can make. The forced of the pistons one one side of the engine are opposed by the pistons moving on the other side. The crank shaft is set at 180 degrees and 90 degrees, depending on the number of cylinders that you have. They are smooth, powerful beauties. But, their "flat" design makes them very wide, which is a disadvantage on a motorcycle, where you want engine to be narrow. However, this flat design keeps the center of gravity very low on a bike, which is a big advantage.

A V engine (2 or 4 cylinder, or that funky 5 cylinder that Honda was making...) puts the cylinders in a very narrow arrangement, since they can be put in front of, and behind, the crank shaft. This makes for a nice configuration for a motorcycle, since the engine is narrow. Also, since the cylinders are angled, the engine is less "tall" than an inline engine, which keeps the center of gravity down. The disadvantage is that the forces inside a v-engine are a bit out of balance. this causes vibration and increased load on the bearings an other moving parts. They shake a bit, and have a slightly lower service life. However, a v-engine creates one of the nicest sounds ever heard in any engine, and this makes them even better suited to motorcycles.

Inline engines are usually in the form of parallel twins, inline 4s, or in the case of the Honda CBX, and inline 6. The pistons are moving parallel, which allows them to be balanced almost as well as a horizontally-opposed engine. This makes them run very smooth. They are a tall engine, which means the center of gravity is higher, which is a disadvantage in a motorcycle, but most manufacturers have found ways of balancing this, so it's not a huge deal. inline engines can really rev, and often you'll see the redline for one around 14,000 RPM in the case of the Honda CBR bikes. (Insane!) Also, and inline has one cylinder head, which means that dual cams requires only one cam chain which saves on parts, makes the engine simpler, and results in fewer moving parts. Since the pistons are usually times at 180 degrees, the ignition can be kept simpler by not seeming a coil for each cylinder. One coil for every 2 works just fine, it's just that every cylinder always has a spark when the pistons comes to the top. Sometimes there fuel and air there, and sometimes it's on the exhaust stroke.

Others will give you more info, but this is at least a start!

--Justin
 

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With 6 cylinders or less an inline has to be superior. That is a tried and true design for decades and very hard to beat. Those old Detroit inline 6's are still running strong, just you can't tear them up.

More than 6 cyclinders and the v's are the way to go, can you say V8?

On our bikes the 2 cylinder v is prolly the worst design for a motor. The only reason it was devloped was to get a bigger motor to fit between our legs. :lol: After it was made it looked really cool so the design stuck and is still with us. But everyone knows that a inline 4 or even a pancake 4 in a sport/touring bike will blow the, er, mirrors off our v-twins.
 

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Right, the V8 (or V12!) is one of the smoothest engine designs ever. Even some V6s, if the firing order and timing is right, can be very smooth. But for 4 cylinders and under, the inline and pancake engines are amazing.

It's true, the V-twin is about the worst engine (from a pure mechanical point of view) that you would want. But the size, sound and look of it make it a winner anyway.

And for what it's worth, the vibration (as long as it's not excessive) is part of the fun. As long as we're not competing for 1/4 mile record-setting times, the V-twin is perfectly adequate power plant for our laid-back cruising motorcycles.

--Justin
 

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Good write-up Justin!!

Dont' forget the V-Twin 90deg that is a horse of a different color when it comes to V-Twins - Especially in the Performance area- Ducati, V-Strom, KTM, etc). They still have all the design limitation of the V-twins with respect to extra cams, chains etc but they are much smoother and produce a butt load of HP for their displacement.

And the V-twins and V-4s that are set in like the Guzzi's and the ST1300 are better at getting power spinning through the trans without having to make a lot of 90deg turns.

Have you ever seen a CBX? They are collectible now, but a wonder to behold......and one of the first winning hondas in the early 60's was an inline 6cyl - 250cc I believe - not sure they made it in 125cc, but it was work of minature proportions and very high rpms. Just tore up the TT tracks.

Seems there was an article I read about engine configs in one of my MC mags just this month - I will have to dig it up.
 

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One other reason the "inlines" got to be very "popular"(read...with bike makers) was the simplified manufacturing process. One could use many of the same machines for engine manufacture from the 2 cyl. to the 6 cyl.(inline) and the V-Twin/V-4 (motorcycle) and the flat 2-4-6 (again motorcycle).

They also have been "centralizing" the engine packages(to help with CG) so as to move the engine CG front/back or up/down. They also "lean"(tilt) the engine block forward to aid in intake air flow OR to help with "handling". On many of the "new bikes...try to get your hands/fingers in/near some of the carb/FI components!

Now, why didn't Yamaha really bring the vertical Twin 850 T-Rex(sounded like a V-Twin...changed the crank timing) for use in the USA. What a machine!!!!!!

Bullzeyet
 

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Excellent description, Justin.
One thing I would add from an engineering viewpoint is that there is nothing inherent to the in-line design that makes them rev higher. It's because of their inherent tallness that the manufacturers tend to make them short stroke anyway, and the short stroke is primarily what leads to a higher rev ability as well as a higher rpm for peak torque. In-line industrial engines are mostly big, long-strokers and turn comparitively low rpms.
On the other hand, the geometry of v-twins lays out easier when the crank throw is longer, so they tend toward the long stroke, low rpm side there.
+1 on all comments re vibration, wear, and esthetics!
 

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Another basic fact is: more cylinders equal less displacement per cylinder for the same overall displacement as a huge v-twin pounder.

The smaller cylinders therefore have smaller pistons, which have less mass, and can change directions much more quickly and smoothly than just two huge steel fists, a la the big Victory engines.

That means much higher rpms and compression ratios can be achieved, overall resulting in a more efficient engine in regards to total weight and hp and torque.

-K
 

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Aaaaaaaah, the sound of a CBX with a Vance & Hines 6 into 1 with no baffles going thru a mile long tunnel on the PA turnpike and "rowing" thru the gears. Just think of the sounds of a F-1 racer or Indy type car at full song !!! Sweeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeett !!!!!!!! :twisted:

Bullzeyet
 

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Discussion Starter #11
gat803 said:
That's simultaneously beautiful and insane! I love it.

Thanks everyone for your commentary. Fascinating topic.

I recall reading motorcycle magazines back in the early 70's and I think someone had a huge one-cylinder bike ... either 500cc or 750cc. Bultaco I think. Given what I've read here about counter balancing and such, how in the world did they keep that bike from shaking apart? The crankshaft must have had a cinder block strapped to it to offset the piston.
 

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For motorcycles:

V-twin: Most displacement in the smallest space

In-Line: Most Power for displacement

Flat/Opposed: Least amount of vibration

Those are the BIG plusses that separate them.
 

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TucsonDon said:
I recall reading motorcycle magazines back in the early 70's and I think someone had a huge one-cylinder bike ... either 500cc or 750cc.
Honda still makes the XR 650.
Single lung thumper powered.
Dual sport scooter, and I have always wanted one.
 

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gat803 said:
TucsonDon said:
I recall reading motorcycle magazines back in the early 70's and I think someone had a huge one-cylinder bike ... either 500cc or 750cc.
Honda still makes the XR 650.
Single lung thumper powered.
Dual sport scooter, and I have always wanted one.
I used to ride a 76 Yamaha 400 single cylinder dirt bike. Take about shake rattle and roll! Talk about a thumper, that was it's nick name, the yellow thumper!

Sweet bike though, it would climb up the side of a building if you could figure out how to make it hold on.

8)
 

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rickbb said:
I used to ride a 76 Yamaha 400 single cylinder dirt bike. Take about shake rattle and roll! Talk about a thumper, that was it's nick name, the yellow thumper!
AIR a friend had one of those... I used to get a kick out of watching it mosey along a dusty road in a high gear, throwing up a little mini-rooster tail of dust every time the cylinder fired.
 

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my FIL had a Suzuki Savage that was a single-cylinder.. I think it was a 650. It was fun to ride, but didn't make nearly the power of my 600 vlx.
 

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tubes_rock said:
Right, the V8 (or V12!) is one of the smoothest engine designs ever. Even some V6s, if the firing order and timing is right, can be very smooth. But for 4 cylinders and under, the inline and pancake engines are amazing.

It's true, the V-twin is about the worst engine (from a pure mechanical point of view) that you would want. But the size, sound and look of it make it a winner anyway.

And for what it's worth, the vibration (as long as it's not excessive) is part of the fun. As long as we're not competing for 1/4 mile record-setting times, the V-twin is perfectly adequate power plant for our laid-back cruising motorcycles.

--Justin
tubes_rock,

In view of some of my research, I've come to the conclusion that if not for balance shafts, inline 4's wouldn't be much to talk about really.

I'm an opposed fan, pure and simple. But...that doesn't mean that an in-line 4 can't be a awesome powerplant, it just means that they need a little more to get there.

I've been under the weather lately and my wife and daughter will be screaming at me if they catch me 'e-mailing'! Gotta go.

EDIT: I'm really pressing my luck here, but I needed to add this.....just think Mitsubisi Evo VS. Subaru WRX. There's some interesting things going on there!

John
 

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Olivereaman said:
tubes_rock,

In view of some of my research, I've come to the conclusion that if not for balance shafts, inline 4's wouldn't be much to talk about really.

I'm an opposed fan, pure and simple. But...that doesn't mean that an in-line 4 can't be a awesome powerplant, it just means that they need a little more to get there.

I've been under the weather lately and my wife and daughter will be screaming at me if they catch me 'e-mailing'! Gotta go.

EDIT: I'm really pressing my luck here, but I needed to add this.....just think Mitsubisi Evo VS. Subaru WRX. There's some interesting things going on there!

John

I'd have to agree. Inline engines do not balance themselves do
to one cylinder being TDC while another is BTD.

Inline engines have massive counter weights on the crankshaft to compensate for rotating assembly. They don't balance themselves.

Now, if you REALLY want a smooth running engine and one that purrs so
pretty... you want a large radial engine. Oh what a beautiful sound!
 

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Discussion Starter #19
litnin said:
Now, if you REALLY want a smooth running engine and one that purrs so pretty... you want a large radial engine. Oh what a beautiful sound!
You're not speaking of a rotary engine, are you? Or are you referring to the type of engine the old WWII planes used to have? Other than for novelty purposes, has anyone every produced a radial engine for either car or motorcycle?
 

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litnin said:
Olivereaman said:
tubes_rock,

In view of some of my research, I've come to the conclusion that if not for balance shafts, inline 4's wouldn't be much to talk about really.

I'm an opposed fan, pure and simple. But...that doesn't mean that an in-line 4 can't be a awesome powerplant, it just means that they need a little more to get there.

I've been under the weather lately and my wife and daughter will be screaming at me if they catch me 'e-mailing'! Gotta go.

EDIT: I'm really pressing my luck here, but I needed to add this.....just think Mitsubisi Evo VS. Subaru WRX. There's some interesting things going on there!

John

I'd have to agree. Inline engines do not balance themselves do
to one cylinder being TDC while another is BTD.

Inline engines have massive counter weights on the crankshaft to compensate for rotating assembly. They don't balance themselves.

Now, if you REALLY want a smooth running engine and one that purrs so
pretty... you want a large radial engine. Oh what a beautiful sound!
Litnin,

Now, if you REALLY want a smooth running engine and one that purrs so
pretty... you want a large radial engine. Oh what a beautiful sound!



No matter what else, that qualifies you from this day forward as my lifelong buddy! :D :D

My Dad took a lot rides in an A-26 powered by two of the finest Pratt & Whitneys ever built, and they brought him back home everytime!! There was a whole lot of hrupmhhh about those v-12's and P-51's and I'm not here to start a argument, but Dad told me enough stories to know what was really what, but when they wanted to get to Germany and back or provide cover from N. Africa to Europe, the men all wanted Radials! High power, light weight, silky smooth, fuel efficient, and dependability were their hallmark! From where I live I can still hear them rumbling overhead once in awhile,.... that distinctive sound is all their's. Their one major drawback was engine oil hydraulic locking in the lower cylinders. With all those cylinders it was very easy to blow a jug completely off the engine if they weren't careful!

I wonder....as much as Harleys get bashed, I wonder what would happen if they continued those cylinders all the way around? I think the might have butchered an otherwise very good design. I wonder what they'd look like? Glenn Curtiss was a true pioneer in both aircraft and motorcycles. I would really like to take some time and study his designs someday.

John
 
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