Triumphrat

zero_B

I'm probably opening up a can of worms here...

"Lifespan" of anything is based on how well its treated and taken care of. I own many old vintage things that have no problem functioning today. Yet, I decided to ask this question.

It always looks to me that anything inline has a tendency of lasting a long time. Inline 4 cylinder cars, parallel twin motorcycle engines, single cylinder thumpers.

Does a V-twin motor last as long?
I always see older V-twin motors with trouble, that is including cars. It seems like their life expectancy is shorter compared to inlines.
Is this true, or is it just me?

Diego

I don't think there's any good way to tell. Too many variables.

"Older V-twin" would mean Harley to most people, and a lot of older Harleys did need a lot of attention. But that was design and manufacturing shortcomings more than anything else. Older parallel twins weren't all that much better.

Inline fours became big about the same time that the Japanese manufacturers realized the perception that motorcycles needed engine overhauls every 25 or 30 thousand miles was a major impediment to mass market acceptance of their product, and they decided it was worth the investment to design better balanced engines (four cylinders make that a little easier), make them of modern alloys, machine them to tighter tolerances, incorporate oil filters, etc. That raised the bar considerably! And, I believe it also coincidentally contributed to the perception that inline is more durable than the V configuration, even though there is no fundamental physical reason why it should be true.

Modern V-twins and parallel twins, built with the same philosophy that revolutionized the Japanese inline-4s, both seem to be almost equally indestructible nowadays.

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John

HiDesert

Hey, what about Ducatis?

There's also Guzzi and Vincent. I'd expect, other variables like metallurgy and production line quality control being equal, that v-engines would be at least as reliable as inline engines. I've heard writers talk about how deceptively fast v-twins are, meaning their torque gets you up to speed without wringing their necks. That could equate to longer engine life, but there are an awful lot of variables to keep track of.

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Catenaccio

To satisfy my own curiosity, I'd love to buy a Moto Guzzi Griso 8v to answer the question. Alas, she who must be obeyed gave me her answer long before I asked.

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Sal Paradise

Inlines share overhead cam shafts, gaskets and carbs or linkages. They have only one head. Inlines are simpler Simplicity =longevity. Inlines are easier to balance. balanced engines dont shake apart.

All else being equal, overhead cam inlines will last longer.

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wabill

You left out this design. Took this and many more pics today.
I've posted more pics at the following site and here's a sample.
http://picasaweb.google.com/screechS3/StillAround#

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Lee

I agree with Deigo that there are too many variables. Manufacturer, models, riding techniques, diligence to maintaining, road types, speeds, weather, cost bracket or quality of the bike and the list goes on. The design of V twin versus inline both have advantages. But as the article below eventually states it is rider preference.

"There are lots of engine options for motorcyclists: Singles, Twins (in parallel, horizontally opposed and Vee configurations), Triples, inline-Fours and V-Fours, horizontally opposed flat-Sixes, rotaries and even jet turbines! Yet with all these options, the most popular engine types for motorcycles have been, and continue to be, V-Twins and inline-Fours. As the pinnacle of motorcycle technology has arguably swayed in favor of the 1000cc Superbike, let’s look at these two engine configurations up close and do a little compare-and-contrast examinations.

V-Twin sportbikes, from the high-dollar Ducati 999S to the low-buck Suzuki SV650S, have been making a strong resurgence in recent times. Excellent midrange performance courtesy of relatively high torque values means easy access to engine power in the hands of the average rider.

But what makes this so? It’s not simply displacement, because in this comparison, we’re only looking at one-liter engines. Instead, the reason V-Twins have relatively more torque than an inline-Four has nothing to do with what you’d expect, such as the engine’s basic layout.

As CW Technical Editor Kevin Cameron explains, “For the most part, this is a function of valve area. The temptation in doing any sports or racing engine is to put into the head the largest valves that will fit. When this is done with a four-cylinder engine (250cc per cylinder in a one-liter Four), the result is more valve area per displacement than with a Twin of the same size (500cc per cylinder in a one-liter V-Twin). The result of this tactic is power concentrated at the top of the rev scale for the four-cylinder, and power concentrated in the middle for the Twin.”

Why is that? It all has to do with intake-charge velocity. When the intake valves open, the downward movement of the piston creates a vacuum (unless you’re running boost, but that’s a story for another day) in the cylinder, drawing a fresh air/fuel mixture into the combustion chamber. Internal-combustion engines are nothing more than glorified air pumps; so because our one-liter inline-Four and V-Twin engines have the same displacement, they therefore flow a similar amount of air per crank revolution. And that means the volume of the incoming charge will be similar in either engine type.



To take advantage of this fact, the engine designers strive to increase the intake velocity of the V-Twins to help them make more peak horsepower, while they try to decrease the intake velocity of inline-Fours so those engines can make more peak torque. What they end up with are two different engine platforms with very similar intake velocities.

“Every competent engine designer attempts to use the highest intake velocity he can get away with,” says Cameron. “In earlier times, sharp port angles and sudden changes of section interfered with flow, so the engineers came to believe that very large ports were necessary. But as better shapes came into being, they found that smaller ports could be made to flow just as much–if not more–air as before. This has been the legacy of the recent ‘flowbench’ period of port development–that small, well-shaped ports can flow plenty of air and improve torque by raising the average velocity in the port.”

We know, however, that Twins and Fours are not equal, and the reason is that there are still limitations that having more open valve area cannot solve. First, as intake velocity is increased, you begin to have a problem with the intake charge reaching supersonic speeds. A shock wave builds inside the intake tract and air begins to “back up” behind the wave. This severely impedes intake velocity and imposes the limit at which an engine can inhale. Additionally, an inline-Four has twice as many power pulses in any given time period than a V-Twin. What’s more, Twins have more frictional losses in the valve train, thanks to needing two sets of slightly larger cams, two cam chains, stiffer springs pushing on larger, heavier valves moving through more lift and, of course, all the bearings necessary to support all the extra hardware.

To counteract the fact that a V-Twin only produces half as many power pulses per crank revolution, you could simply make the engine rev higher. But even if you were able to ignore the frictional losses (which increase by the square in relation to cam rotation speed–and remember, you have four cams pushing on the aforementioned bigger valves and hardware), you’d run into an even bigger issue, in fact the biggest issue: piston speed.

“What really determines how high an engine can rev is its peak piston acceleration, reached at TDC on every revolution. This is typically something like 7000 gs right now. Above that, there are problems with piston and ring reliability. Peak piston acceleration is directly proportional to stroke length, and to the square of rpm. In Superbike racing’s previous 1000cc Twin/750cc four-cylinder formula, this difference worked in favor of the Twins, even though the formula had been carefully set up so that the difference in displacement would be offset by the smaller engine’s shorter stroke and ability to rev higher. But in fact, the Fours could not rev as high as that formula assumed, because they reached that maximum piston acceleration sooner than thought.”

From an engineering standpoint, torque alone doesn’t make an engine configuration viable. That’s why packaging has played such a strong role in the success of the V-Twin. Not only are V-Twins narrower, but contrary to popular belief, they offer greater flexibility in fore-aft weight distribution due to their broader polar moment. Inline-Fours, on the other hand, are wider than V-Twins, obviously, but longitudinally shorter. In a front-to-rear plane, at least, that shortness is helpful in achieving the “mass centralization” goals that most sportbike manufacturers currently ascribe to. But the width of inline-Fours means they are generally harder to flick side-to-side than their V-Twin counterparts.

But wait! There’s more. By utilizing a shorter stroke, with smaller valves in smaller bores, Fours can rev much higher than Twins can. And because a smaller bore size means a smaller combustion chamber, the mixture is likely to burn more completely because the flame front has a shorter distance to travel; and that, in turn, allows the use of higher compression ratios. All of these factors equate to an engine that produces more peak horsepower than a Twin. No matter what sort of engine format you like, more power pulses per revolution, with more revolutions available over a given time period, equal more power

Then there’s the subjective feeling that V-Twins provide. Producing one large power cycle per crank revolution, and staging those pulses at staggered intervals, not only yields a character that can be felt and heard, it punches all the right feel-good buttons.

Does that mean inline-Fours are better? Absolutely not. As Cameron puts it, “In simple terms, the four-cylinder should slaughter the Twin in terms of power, but when can you use it? For a few seconds at the end of the straights? Meanwhile, the strong midrange of the Twin can allow its rider to get a better jump off most turns, which gives an advantage most of the way down the next straight.”

What all this means is that, unless you’re involved in a serious racing program, it doesn’t really matter what motor layout powers your bike. Whether it’s a torquey V-Twin or a high-revving inline-Four, the bottom line is that a rider’s emotional preference is, as is often the case, the only real measuring stick that matters.
– Calvin Kim

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miker

IMO, it's not the configuration of the engine, but the stresses it's put under.

I have a 1995 Jeep Cherokee with almost 300,000km on the clock. It doesn't burn oil, doesn't use water and whilst it's a bit rattly in the top end is as solid as a rock, even though it may be a little down on HP to what it was new.

I have a 1982 Harley, it's got over 160,000km on the clock, it's had a complete rebuild about 30,000km ago, but not because it failed, but because it may have failed. I didn't know it very well, so wanted to make sure. It also doesn't burn oil, it just goes and goes.

My Speed Triple on the other hand at 100,000km was starting to feel a little tired, there weren't many more more valve adjustments available, so it was perhaps going to at least need a head rebuild in the near future.

Then, take the actual revolutions required to run the same distance. Without doing the calcs, I'd have to say that the Speed Triple engine, with a red line of 9,000rpm and a cruising rpm of around 4,000 to 5,000rpm, may have spun over more in it's 100,000km, than a Harley travelling twice the distance, because they redline at a lower rev range, and require only about 2,500 - 4,000 rpm to give the same cruising speed. The Jeep is the same at 100kph the tacho is at about 2,000rpm. My son's Hyundai Excel is at 3,000 rpm. It's done 120,000 km and is toast, burning oil and using water.

These are just anecdotes of course, but in my experience and opinion when it comes to bench racing, an engine with a lot of torque will out last an engine with a lot of horsepower any time.

Mick

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GuzziT

while i appreciate the jack kerouac reference, i must disagree with your statement. a straight 6 and a 90 degree V twin are about the only perfectly balanced engines. in line 4s require some sort of balance shaft.

and as far as longevity, guzzis do 100k frequently.

http://www.guzzitech.com/100k/100k.html

Skull Crusher

Actually a 5 cylinder is almost perfectly balanced.

Cheers

Jeff: