The Pros and Cons of Every Motorcycle Engine Type

Hello, this is why you should seek, or avoid, each type of engine. Foundationally, we have our single. One piston and one cylinder. The biggest benefit is cost. I only need one carburetor, one cylinder head, one valve train, one exhaust system. Short of sticking a Roman candle up your butt, this is as cheap as internal combustion gets. I choose singles when I'm buying old pieces of ----, because this hides very few surprises. Another benefit is long power gaps. Four strokes only make boom on one of four strokes. Or 180 degrees of the 720 degree crankshaft cycle, meaning singles have 540 degrees of silence. And they go bang, rest, rest, rest, bang, rest, rest, rest. At the rear wheel, in top gear, that might only be one power pulse per revolution of the tire, giving your rubber all this time to recover grip. So singles make the best dirt bikes. Twist your wrist and you'll slide the tire for one fraction of one revolution, making it forgiving to feel the edge of traction, since you won't lose the whole tire at once. However, it sounds like a lawnmower. The cadence thump, thump, thump, is why singles are nicknamed thumpers. Another downside is vibration. We have one piston moving up and down, one counterweight moving down and up. So we're left playing shake the weight, fore, and aft. And this is why singles shake a lot, and generally can't exceed 7,000 RPM without rattling to pieces. And there are also limits on how big a piston can get before falling apart, so singles tend to top out around 650 cc. At 7,000 RPM, that's very slow. To go faster, we must increase capacity by adding more cylinders. The easiest and oldest method being the V-twin. See, our pistons attack from two angles, so we can use the same crank pin on the same crankshaft, but get double the power. Early V-twins weren't even bulkier than singles, only 20 degrees between cylinders. However, modern big-bore engines use wide pistons, and their skirts crack, crack, crack into each other at bottom dead center, so the V had to widen. And widen. Today's Vs are usually 50 degrees apart or more. Ducati famously calls their 90-degree jobs L-twins. Such spacing means we need two discrete fueling systems, two cylinder heads, two valve trains, two cam drives, double friction loss, double complexity, double cost, and there's worse. To snorkel air between your cylinders kills half your fuel tank volume. And think of the heat! How are we to keep our fresh charge cool when it's wedged between two pistons? How are we to prevent the rear cylinder overheating when it's sheltered behind the front? It's an inescapably awkward shape to fit in a motorcycle. There's free space I have but can't really use, and filled space I wish I could use for the swingarm pivot, but can't. So V-twins tend to get really long. And cruiser bikes that prefer straight roads. After a complete circle of the city, the racer who returns first before the record stops, wins the right to seek the prize. Enter the narrow mazeways of London, where Brits pioneer something more compact, the inline twin. With two pistons side by side, inline twins are horizontally short. Also we can once again use one head, one valve train, one cam drive. The intakes are all on the right side, the exhausts all naturally on the other. There's reason inline twins are the most used motorcycle engines. However, because the pistons are side by side, inline twins necessitate a longer crankshaft with separate crank pins. Like a fat kid approaching the teeter-totter, we're staring down a significant balance problem. Your first thought is to fire the twins 180 degrees apart. So when one piston flies up, the other flies down, seems balanced. And it is in one axis. See look, the pistons act on different points of the crankshaft. So while one pulls up here, the other one pushes down here. Rock, rock, rock, rock. It's called a rocking couple. Now, what's annoyingly buzzy on a motorcycle can be catastrophic on a wooden airplane. It was a bad show to have crashed an aircraft. So World War I aero engineer Max Fritz built boxer twins, two pistons punching straight at each other. You can see that the piston forces are inherently balanced. And because the heads don't have to clear each other, they can act on very nearly the same point of the crankshaft. No rocking couple. And since the cylinders are flat, it's easier to pump oil into the engine. Less fighting gravity, free horsepower. The pros stack up compellingly if you have a 40-foot wingspan. BMW famously had to bribe Max, with a coal stove in war-ravaged Germany, to even consider putting a boxer twin on a motorcycle. It's an illogical choice for carving corners or cutting through trees, and must be fueled with the tears of engineers. But boxers became iconic for the more mature riders. And remain so, largely because the low center of gravity makes it easy for old men to pick up off a sidestand. Next on my shitlist of engines is the inline triple. Three ducks in a row, and if you look carefully, you'll notice at least one piston is always moving. See, on singles and twins, there's a moment of dead stop. Either at top dead center, bottom dead center, or one of each, no piston is moving. And we call this inertial imbalance, because it makes the crankshaft go whoosh, whoosh, whoosh, speeding and slowing every rotation. But on a triple, if this piston is stopped, these two are moving. If this piston is stopped, these two are moving. Momentum is equalized across the crankshaft, so it can spool up faster, hitting higher revs. We know power is proportional to the multiple of RPM, so triples can hit the highest horsepower yet, and as the Jehovah's Witnesses would say, you've now heard the good news. Because the rest is bad. Three is an uneven number of cylinders, and a three-legged dog will never hump smoothly. We could balance it in Y, and that would cock up X. We could balance it in X, and oh, that would ruin Y. Add one balancer shaft, two, ten, it doesn't freaking matter. Triples will always shake, and that annoys the perfectionist in me. So let's one-up to the inline four. A nice even number. Remember our 720-degree cycle, divided by four cylinders, and then subtract the 180-degree length of a power stroke to get zero, as in zero time that the crankshaft is not receiving power. Zero silence. And for the first time, it's not bum bum bum. It's buuuuuuuuuuuuuuuuh! Which is why inline fours are nicknamed screamers. Oh! Screamers balance all pistons and both rocking couples, so they can spin extremely fast. It's maximal power per displacement. However, there is one significant con. A sneaky little ---- called secondary imbalance. Here's our piston on our crank. Top dead center, and then 90 degrees, and then bottom dead center, then 270 degrees, and then top again. But because Pythagoras was a little bitch, this height, it's not actually halfway. It's a little bit less than half. So our piston must move faster to get here, and slower to get there, slower again to get there, and faster again to get back up there. That means some force must exist at mid-stroke to change the piston velocity, versus top and bottom. Bullshit! Inline fours have the worst possible secondary imbalance, then. It's not fatal. Engineers just add a balancer shaft to fix it. But geeks hate moving weight around. That's why I never go to the gym. Our only solution is the unicorn, the unattainable, the inline six. We're talking Honda CBX. We're talking Kawasaki Z1300. We're talking Benelli A song sung but three times that still rings in our ears. Do you hear the theoretical perfection? Our inline six is the smallest possible engine with perfect balance. All primary forces, all rock and couples, all secondary forces, are naturally neutral. Even the crankcase volume stays continuous so as not to incur pumping losses compressing air. But, and this is a wide bariatric but, we are back to the boxer problem. What is the point of having a lovely engine that turns into a road crayon at 30 degrees of lean? Let's take a step back and rearrange our inline four into a v-four. I admit the secondary forces don't cancel, but because of the v-angle, well, they don't add one to one either. It's more like one plus one equals one point four. We have a smaller rocking force acting on a shorter crankshaft. And because sequential pistons are now on opposite sides of the engine, we can use large bores without needing a long block. I'll stand behind a bold statement. The v-four is the best engine for a motorcycle, period. Near perfect balance, allowing for 20,000 rpm big bore power in a conveniently sized square. Just look at the MotoGP grid. Ducati, Aprilia, KTM, Honda, 20 of the 22 fastest motorcycles in the world run v-fours. However, those motorcycles cost 1.5 million dollars. And to fit four pistons on half the crankshaft requires crepe thin webs and bearings. And to get that, you basically have to employ to machine them from adamantium. Honda once spent for their VFR. Yamaha for their VMAX. Ducati's Panigale. Aprilia's RSV. But they're generally unobtainium. So if you get a chance to own a v-four, do it. Singles are for saving money and riding dirt. V-twins add power if you mind adding length. Inline twins kind of lope along and sound like a sewing machine, unless it's one of the new 270 degree jobs. Boxers are dumb. Inline triples are inherently unbalanced. You'll see these marketed as raw engines, but I sold you a raw hamburger. Would that be desirable? Inline fours are the first true screamers. Constant power being a better way to rev fast, though you'll need a balancer shaft. And inline sixes are theoretical perfection, but realistically impractical. We've been gradually adding width and cost, and this is the point of diminishing return. Thank you very much for watching. And yes, I left a few engines out. I can't talk about them all at once any more than I could ride them all at once, which is why VOOM deserves your attention. VOOM is an insurance provider that offers pay per mile coverage. You snap a photo of your odometer each month and pay just for the distance traveled. Why hold full-size insurance policies for multiple part-time bikes, or even for one bike if you ride less than 2,000 miles a year? Click the link below and make a quote. If you live in one of these states, you could save up to 60% on motorcycle insurance right now. Click the link, make a quote, and see what you get.