V-twin (Guzzi) vs Flat-twin (BMW)

[Cool Runnings]

I may have missed something , technically a boxer motor is a a 180 degree twin with a crankshaft that effectively mimics a 360 degree twin because both pistons move in and out together . Different from a 180 degree vertical twin . I think Huzo was referring to a vert twin with a 180 degree crank .

 Dusty

Now that's not how one boxes 

[Tom]

No....but Boxing day is just around the corner.   

http://ukbankholidaydates.co.uk/boxing-day/
http://www.timeanddate.com/holidays/canada/boxing-day

[jas67]

Did those old 180 cranks have evenly spaced firing intervals ? I can understand in a two stroke with a power pulse every 180 deg, but how did they do it with a four stroke given that there is an exhaust stroke every second one ?

No, the 180 crank four strokes do not have evenly spaced firing intervals.     They're more like:

++------++------++------++------

vs the 360 crank motor's:
+---+---+---+---+---+---+---+---

So, they're actually  more uneven than a 90 degree V like a Guzzi

[Triple Jim]

Now that Dusty, jas67 and I have all said the same thing, it's starting to sound like we think Huzo needs special attention.   

[oldbike54]

Now that Dusty, jas67 and I have all said the same thing, it's starting to sound like we think Huzo needs special attention.   

 He does , he does  Seriously , I was just trying to clarify the concept . Huzo is a smart guy , it was probably me who was confused 

 Now let's discuss the engineering principals behind Twingles   

 Dusty

[ohiorider]

Way too much time on my hands when I made these 4 powerpoint slides (converted to jpg)  Hopefully, it'll run in slideshow mode when you open it.

http://s115.photobucket.com/user/bcgilligan/slideshow/BMW%20Crankshaft?sort=3

Bob

[LowRyter]

Most of the Beemers I've ridden have been boring and mediocre performers.

The Guzzis are engaging and have a little kick in the pants when your rev them.

But the new water boxers have moved the Beemers into another level of performance.  There's no Guzzi offered now that offers the excitement and power.  Perhaps it will change if we get a 1400 sport tourer?   But not now.

[tpeever]

Bought my first Airhead last fall. R75/6. Never owned or ridden one before. Gave it a top end restore this past winter and have been riding it pretty regularly. I really like the bike but I think I agree that Guzzis have more soul and sound better. The Airhead has very nice torque and is much smoother than a Guzzi. Very capable machine. Oozes quality.

[Triple Jim]

tpeever, that sounds a lot like the way I feel about an R75/5 a friend of mine got not long ago. 

[Huzo]

Now that Dusty, jas67 and I have all said the same thing, it's starting to sound like we think Huzo needs special attention.   

Yep it's just possible you're right Triple Jim, the truth is I was referring to vertical twins and instead of starting a bun fight which I seem to do all to readily in certain company.... I thought I'd phrase my query as a question. See here's the thing, anyone who tells me that a parallel twin has a 180 deg crank had better accept the fact that when one piston is at tdc the other is at bdc and if you plot the intervals out on a straight line as was just done before this post, the offbeat pulses are apparent. I'm just not sure everyone here was on the same page. Thanks for the compliment Dusty, but a bit of "special attention" never goes astray.

[Triple Jim]

Ha, well, I think the confusion came when I thought you were asking about the 180 degree crankshaft of a BMW.  Then after Dusty's post, I realized you were asking about parallel twins.

Interestingly, they are still around in numbers.  All the Ninja twins are 180 degree cranks, as far as I can tell.  My 250 is, as is the 500 and 650.  My assumption is that if you want to rev really fast, it's better to have the pistons traveling opposite each other for balance, than having them going up and down together, essentially one big single, as far as balance.  My 250's redline is at 14,000 rpm, and at that speed no one could possibly tell what the firing intervals are.   

[Huzo]

No, the 180 crank four strokes do not have evenly spaced firing intervals.     They're more like:

++------++------++------++------

vs the 360 crank motor's:
+---+---+---+---+---+---+---+---

So, they're actually  more uneven than a 90 degree V like a Guzzi

Yeah Jas 67, that's what I'm talkin' about, but here's one I don't know, why do you think they would do a 180 deg crank on a vertical 4 stroke twin in the first place and I'm not saying they didn't. What would be the perceived benefit over a 360 deg crank where both are at tdc at the same time ? I've heard the b.s. about v twins have more torque than comparable parallel twins of the same bore/ stroke but isn't each cylinder independent of the other and just contributing it's own share of the available torque, and doesn't "know" what the other is doing, I'm wondering if you got a torquey v twin and managed to re arrange the cylinders so they fired 360 deg apart, what do you reckon the new max torque figure would be ? Just asking out of interest, but would love to hear an informed (or otherwise) opinion. Huzo.

[Huzo]

Ha, well, I think the confusion came when I thought you were asking about the 180 degree crankshaft of a BMW.  Then after Dusty's post, I realized you were asking about parallel twins.

Interestingly, they are still around in numbers.  All the Ninja twins are 180 degree cranks, as far as I can tell.  My 250 is, as is the 500 and 650.  My assumption is that if you want to rev really fast, it's better to have the pistons traveling opposite each other for balance, than having them going up and down together, essentially one big single, as far as balance.  My 250's redline is at 14,000 rpm, and at that speed no one could possibly tell what the firing intervals are.   

No worries triple Jim, this is a damn good thread, I love it !!!

[oldbike54]

 So it wasn't me who was confused ???? Hell , that might be a first 

 Dusty

[Huzo]

Take heart oh Dusty one....I'm confused as to who was confused !!? How about we talk about bikes !

[ejs]

V-2 & 270° tvin & crossplane do not have all pistons at end of stroke at same time.
Therefore they have less internal loss of power, I think...:-)

[Triple Jim]

The main problem with all the pistons reaching TDC and BTC at the same time is rotational vibration.  When all the pistons are coming to a stop, the crankshaft gets sped up a little, and when it speeds them up again, it gets an opposite rotational force that slows it down a little, so rotation isn't quite smooth.

Most inline 4-cylinder engines have crankshafts that start and stop all the pistons at the same time too, with the "crossplane" crankshaft type avoiding it, but getting uneven firing instead.

[kirby1923]

Yeah Jas 67, that's what I'm talkin' about, but here's one I don't know, why do you think they would do a 180 deg crank on a vertical 4 stroke twin in the first place and I'm not saying they didn't. What would be the perceived benefit over a 360 deg crank where both are at tdc at the same time ? I've heard the b.s. about v twins have more torque than comparable parallel twins of the same bore/ stroke but isn't each cylinder independent of the other and just contributing it's own share of the available torque, and doesn't "know" what the other is doing, I'm wondering if you got a torquey v twin and managed to re arrange the cylinders so they fired 360 deg apart, what do you reckon the new max torque figure would be ? Just asking out of interest, but would love to hear an informed (or otherwise) opinion. Huzo.

One of the advantages of the 360 deg is traction is better but they sound funny, especially the 90 deg V 4. Most like the sound of the 180 better also. (A big deal)

:-)

[JJ]

Back in the day, I bought a new, red 1983 BMW R80RT (like the one in this photo). It was my only transportation at the time.  Overall, it was a very practical ride with full fairing and removable hard bags.   

It did not have the performance or soul of a Guzzi, but I put >50,000 trouble free miles on that airhead, other than 1 broken clutch cable, tires, and a battery.

[Huzo]

One of the advantages of the 360 deg is traction is better but they sound funny, especially the 90 deg V 4. Most like the sound of the 180 better also. (A big deal)

:-)

Yeah, don't want to thrash this to death, but some of that is gunna take me a while.....

[oldbike54]

 The early 1000 CC airheads (up to '84) are faster than they feel , kind of like an electric motor . Many have said that they felt slow , but both of mine would hold their own with supposedly faster bikes .

 Funny story , there is a guy here in Muskogee that we rode with some in the '90's -'00s . He bought an Ultra Classic in '97 , and proceeded to spend money to make it faster . He the proceeded to buy newer , larger displacement BT's and buy the performance mods . Once a year he challenged my '84 1000 CC beemer , I really didn't think much about it , and even mentioned to him that the 2005 or so RK with a big bore kit and other mods ran pretty good . His son , also a Harley guy , stated , "Dad was not going to stop until he owned a Harley BT that would outrun your old beemer" . Well , maybe $75K later he did have one that would , but just barely 

 Dusty

[JJ]

IMHO, here is another underrated airhead Beemer, the iconic BMW R90S Never owned one, but have ridden several. Cool bike! :1:

Years produced: 1974-1976
Total production: 17,378
Claimed power: 67bhp @ 7,000rpm
Top speed: 125mph
Engine type: 900cc, two-valve, horizontally opposed twin
Weight: 215kg (474lb) wet
Price then: $3,430 (1974)
Price now: $3,500-$12,500+

[Jake]

Had an R80RT - good bike - about 3/4's of the soul of my 850T.   The Beemer is smoother, the T is more voracious.  Liked the Beemer, love the Goose. 
Now have a R750/7 RT to get back into shape.  Rode it before - not much real soul, but it pulls all day long, takes a minute to get up to speed, but still like the big twin thing versus the Jap bikes. 

[Tom]

I just rev'em the nature of the bike and engine comes out.  Didn't appreciate the K75S till I was able to spend the day with one.  I was on a F650 and the friend had the K75S.  Low rpm's felt like a twin, higher rev's like 4.

The R1100RT has grown on me as a capable tourer.  I like the looks however of a R100RT or R80RT but I'd like to get the R90S that I know is available to select people in Honolulu.

[swooshdave]

One of the advantages of the 360 deg is traction is better but they sound funny, especially the 90 deg V 4. Most like the sound of the 180 better also. (A big deal)

:-)

For dirt tracking they tend to like 270˚ because it doesn't put the power down evenly.

[Lannis]

I'll be honest, I don't really care what my bike "sounds" like.   I've had V-twin Harleys, a BMW airhead, multiple British twins and singles, single and twin two-strokes, and two triples.

I have no idea what kind of "character" and "soul" a bike has until it has:

1) Started up for me on a freezing morning.

2) Started up after marinating in rainwater for three days.

3)  Carried me over dark mountains in foul conditions without missing a beat.

4)  Carried me in the flow of traffic at 70 MPH in the fast lane, boxed in between three trucks and a bridge guardrail.

5)  Carried on after hitting an unexpected pothole, leaned way over on a guardrail-less mountain road.

6)  Gotten me home with a big load on blazing hot day through the hills.

A bike that will do that for me (and there have been many) has CHARACTER and SOUL, I don't care how many pistons it has, how big they are, or what order it fires them in.

Lannis

[kirby1923]

I think its more about the time between the power strokes that matters on dirt. That's why the HD with the 45 deg firing has done so well on the dirt because of the long time between power strokes allows the tire to keep better traction by letting the it recover from strokes of power.

I do believe that sound is important to most (a lot of riders) and useful in marketing.

I think I heard that HD tried? to patent the sound of the 45 deg engine configuration. 

[Triple Jim]

I think its more about the time between the power strokes that matters on dirt. That's why the HD with the 45 deg firing has done so well on the dirt because of the long time between power strokes

As is sometimes said "not to be pedantic", but the 45 degree Harley engine firing intervals are 315 degrees and 405 degrees of crank rotation between power strokes.

[kirby1923]

As is sometimes said "not to be pedantic", but the 45 degree Harley engine firing intervals are 315 degrees and 405 degrees of crank rotation between power strokes.

"
A narrow angle V-twin such as the 45° Harley-Davidson naturally has slightly unevenly spaced power strokes. By changing the ignition timing on one of the cylinders by 360° the power strokes are very closely spaced. This will cause uneven fuel distribution in an engine with a single carburettor. The Harley-Davidson XR-750 with twin carburettors was a popular bike to twingle. It had great success in flattrack racing.[citation "

[Lesman]

I had a GSPD for 19 years. I've owned a Guzzi for 5 years(2 years it was partially a part). For the most part . The Guzzi is a simply, more practical version of the BMW airhead. The Guzzi handles better(The BMW is also a pretty good handler), stops better and gas mileage is  dramatically less than a BMW airhead. The Guzzi doesn't nickle and dime you to death over simple repairs.
Most people think Guzzi riders are the guys that ate paste in Elementary. I like my Paste with Hot sauce.
Guzzi may have more character but BMW's are not soul less sewing machines. 
Why are Guzzi's superior to BMW? There is at least one person with a Moto Guzzi tattoo(WayLongWay).