Cylinder Offset Changes Everything
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Published 2023-03-26
If you observe these two engines in rotation you can see that they do the same thing. The crankshaft rotates, the piston reciprocates, the rod does it’s own thing. However this is nothing other than a superficial illusion, because this little offset actually changes everything. Despite being made from the same parts these two engines are fundamentally different. The cylinder offset impacts power and efficiency as well as engine size, it dramatically influences engine balance and it disrupts the length and duration of the piston strokes. And in this video we will explain how and why all of this happens and why many recent engines employ an offset cylinder configuration. We will start simple and then gradually increase the level of mind-bogglingness until you get completely sick and disgusted of looking at these two engines and close this video. Let’s see how long you can last.
So let’s start easy. Heres’ the first fact: The offset cylinder engine makes more power and is more efficient. Why? Let’s imagine that both pistons are just a bit past the start of the combustion event
So we have combustion pressure building inside the chamber resulting in massive forces pushing down on the piston. But the piston is obviously connected to the crankshaft via a wrist pin which means that the piston also pushes down on the rod and then the rod pushes down on the crankshaft. The problem lies in the fact that the rod is inclined at a certain angle. The downward force exerted on the rod is directed at the small end of the rod, meaning that this force is actually trying to spin the rod or flip it over if you will. As the rod tries to flip over it ends up pushing the piston against the cylinder wall which increases friction. The sharper the angle of the rod the harder the rod pushes the piston into the cylinder wall and the greater the friction. As you can see the offset cylinder allows us to noticeably reduce the angle of the rod which reduces friction. Reduced friction means that less of the energy generated by the engine gets wasted on friction which means that there’s more available to be converted into usable work a.k.a power.
Next up let’s talk about size. Yamaha on their website claim that an offset cylinder engine is more compact. Now this isn’t a lie per se, but this statement is only true under certain conditions. As you can see in our example both engines are of the same size. In fact the offset actually makes this engine wider overall. So why did Yamaha say this? Well they said it because the only other way to reduce cylinder friction is to make the connecting rod longer. As you can see if we make a zero offset engine with a longer rod the resulting rod angle ends up being noticeably reduced which leads to reduced friction, however the a longer rod obviously leads to a much taller engine. So basically what Yamaha is trying to say is that a zero cylinder offset engine can’t have reduced friction without being taller because of its increased rod length. So the offset cylinder engine is only more compact than when compared against a zero offset engine with a longer rod.
Now let’s address something that you have probably already noticed. The offset cylinder engine obviously has a longer stroke. How is this possible if the crankshaft is the same? As we know, an engine’s stroke or the distance the piston travels from top dead center to bottom dead center is determined by the length of the crankshaft throw or the distance between the center of the main journal and the rod journal. This distance is what determines the diameter of the imaginary circle drawn by the crankshaft during rotation and the distance between these two points on the circle ends up being the stroke of the piston.
On the offset engine bottom dead center is here. As you can see the line which connects the crankshaft with the piston is obviously longer in the case of the offset engine because this line is at an angle. Now what connects the piston to the crankshaft is obviously the connecting rod which means that in order to retain the same stroke the offset engine would have to employ a longer rod. If you keep the rod length the same it means that this line is forced to become shorter which pulls down the piston an additional distance which increases stroke.
00:00 Power and efficiency
03:31 Stroke length
05:35 Unequal strokes
15:06 Balance
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#d4a #cylinderoffset #enginebalance
All Comments (21)
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100 cars that changed the world: amzn.to/3DGXDf6 Stem engine model: amzn.to/3Y5iZLv Motivation: www.youtube.com/channel/UCt3YSIPcvJsYbwGCDLNiIKA 1-2-3 count with Car parts: amzn.to/3jxP7Z6 Patreon: www.patreon.com/d4a
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Your calm, gentle tone without any background music or sudden, "startling" audio tracks makes this channel leagues ahead of others. No distractions. Just pure education. Thank you! ❤❤❤❤
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I love these videos, you have a great ability to take deep dive into a complicated, almost nerdy subtopic, and illustrate it in a lighthearted and engaging manner.
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In the trucking world the offset cylinder (commonly referred to as downsped engine) does wonders for the engine performance. Slower piston speed means more torque at lower rpms while increasing fuel efficiency. It also increases exhaust temperatures which helps with all the emissions components. Pretty amazing to move up to 80000lbs at 950rpms at 65mph and getting 10-12mpg.
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I am a automobile teaching professor the degree angle of rotation was explained phenomenaly hats off i will recommend this video to my students and show this video in my coming lectures
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So many of academic books seem like they are written for people who already understand topic at hand. Your approach is complete opposite of those boring and soul crushing books. Thank you! D4A channel is top tier! Your passion and dedication shows, and it's obvious you have a lot of empathy and understanding for those of us who are at the beginning of our learning journeys.
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People are always surprised how well these videos take complicated topics and explain them clearly step by step. That's what we need to teach kids in school - the way to organise your thoughts in to small chunks, put them in a timeline in a correct order and present them to others. It's reading, writing and critical thinking working together to produce successful communication. That way you accurately express your thoughts, the other person understands them as you meant it and everybody is on the same page. Also, that's how you teach others. Also, it's THE way to erradicate common misunderstandings and arguments people get into simply cause they got each other wrong. All the fights in the comments sections, under news articles, in the public arena, in the media... You need to learn to think like an engineer, in logical steps. Then you can explain a trip to Mars to a 5-year old.
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Many years ago as a student I visualized this idea of an offset crank and wondered if it would develop more torque. Thanks for so thoroughly exploring and explaining this topic. Fascinating.
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Not a engine person at all but you break down the Physics so simply and speak with such a passion that its a joy to watch.
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I'm a mechanic with some engineering experience and your videos are amazing for bridging the gap between practical and theoretical knowledge. The way you teach by gradually introducing the mathematical concepts alongside the practical demonstrations make your explanations work. I'm sure someone with no engine experience would struggle, but I think your videos are an excellent resource for people like me who need more theory, or people like engineers who understand the theory but rarely work with the actual application.
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I love your style. The combo of personality, accuracy, detail and pace is perfect. I've been teaching for 27 years and it's is rare to find these properties, all in one presenter. Thank you.
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Seeing this video is a bit of a shock! I proposed this idea to General Motors (I was a Chevy guy then) about 60 years ago! I had built a flat model where I could tilt the "cylinder" to create an offset and crudely measure the change in intake/power strokes to the compression/exhaust strokes. I sent them a letter and some drawings mostly stressing the benefits of increased duration of the intake and power strokes. I had figured out most of what you cover in your video save for the vibration issues. I believed the vibration wouldn't change with a cylinder offset. I think I also missed the different stroke lengths but hey, I was only 15 or so at the time. To my great surprise, GM responded! They said they had tested the idea and it didn't yield any noticeable benefit. Did they just blow me off or had they really tested it? If they did test it, did they change the ignition and valve timing, I'll never know. Great video! 👍
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Explaining relatively complex things in a comprehensive way requires serious knowledge. Great video! Thank you for sharing it!
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It's amazing how changing a single parameter (crankshaft offset) produces such complicated knock-on effects for a multitude of other parameters. Thank you for breaking it down and making such a complicated amalgamation of forces understandable!
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Excellent video! You missed one very important point. The offset cylinder moves the point of maximum combustion pressure closer to the point of maximum mechanical advantage. Also, the same effect is often achieved with an offset piston pin location in the piston design. The lengthened intake stroke duration is very helpful in naturally aspirated engines. Getting air in is much more difficult than getting it out!
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Haven't learned as much about an engine since I learned about combustion cycles at 8, about 35 years ago! Great video!
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I learn so much from your channel. I've built several engines in my lifetime and have worked as a mechanic in the past. Videos like this show me the gap between what I KNOW and what I fully UNDERSTAND. Thank you and please keep the lessons coming.
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The "classic" mechanical name for crankshaft offset from center bore line is "DeSaxe" offset. It has been used for nearly 90 years (off and on) for Two Stroke engines (especially Model Airplane engines), but there were even some stationary steam engines which were "DeSaxe'd". Up until only recently, vibration and harmonics were always a problem. Kawasaki first used it on some of their big bikes in the early 2000's but didn't quite get it right for some time. Now, it's pretty common. Back in the early 1990's my automotive mechanical engineering professor said there was nothing new (un-tried) in internal combustion engines for nearly 60 years... he was right. Many of the first attempts were way ahead of the technology (particularly materials, and understanding the concepts of good combustion chamber design). We take for granted CAD and Fluid Dynamics modelling software and digital ECUs. Back then, they had slide rules, sine and cosine tables. Perhaps the most advanced thing available in the late 1950's was something akin to an oxygen sensor (the size of a tanker desk) in the engineering area... times have changed. Great Video!
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I had no idea of this technology . Your explanation of this was very clear. I can only imagine the time spent editing this video. Thank you for your time and effort to create this.
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I made it to the end! When I was young I raced bicycles. All of the dynamics you have mentioned are directly related to bicycles. When you are starting at the line no one in they’re right mind would set the peddle at the twelve o clock point. You might even hurt yourself if the peddle can move freely in reverse. Seat position forward and back are important as is seat height. I never thought about why some of the practices we used were helping. Great video!
