BMW R1200R R1150R/T F800 K1200R R1100R/T R1250R RnineT Message Board

And other BMW Boxer engine design features and engineering decisions.

Stolen, copied, extracted, and reused...

"THE BMW BOXER CONCEPT: ADVANTAGES AND DISADVANTAGES (A QUESTION OF PRINCIPLE)

Both Boxer motors and the K series are built on the same fundamental principles at BMW (automotive design - trans. note). The construction principle: crankcase with additional cast bell-housing for the dry clutch and starter drive gear. Bolted up to this is a separate transmission housing containing the final drive output shaft. All the shafts are oriented in the same direction. In the world of motorcycling manufacturers today, only Moto-Guzzi retains an identical construction concept.

ADVANTAGES:
Motor and transmission as separate entities may make later repairs more economical, since less labor time is required to service separate components.
The separate gearbox can be lubricated with special transmission oil. Thus in principle it should be possible to provide a "lifetime" lubricant. The oil remains clean forever, since there is no wear material from the dry clutch being deposited in the oil (as would be the case with a wet clutch - trans. note).
The motor lubricant is not burdened with the wear and contamination of the transmission and clutch. Thus longer oil change intervals can be recommended.
All rotating shafts are lying parallel in the same plane, resulting in better mechanical efficiency.
DISADVANTAGES:
Noise suppression of the separate transmission and crankcase housings and large dry clutch bell housing is not very effective. The primary drive reduction must take place in the transmission after the clutch. This increases the rotating masses in the transmission. This has an adverse effect on shifting comfort and noise when changing gears.
Crankshaft rotation perpendicular to the rotation of the wheels may have an adverse effect on chassis stability.
Crankshaft torque reaction is not cancelled by a counter-rotating clutch or similar heavy rotating mass.
The motorcycle leans along its long axis under acceleration. This constructions results in a long engine/transmission package. Thus a shorter wheelbase, desirable for good handling, is scarcely possible.
Shaft drive vastly increases the unsprung weight of the the rear wheel assembly. This impairs the suspension behavior of the machine.
Shaft drive mandates a wide separation of the footpegs. This is not ideal for the seating position."

Damn good reading at bedtime ... but, I still love my R.

As with any design, there are trade-offs. But, IMO, the Rs are the most intelligent motorcycle design out there.

Keith

Mike

It was very hard for me to masticate your word representation......I was both wonderfully happy and confused.

The only thing that comes to mind is:

Have you ever been fortunate to have to change a clutch on your R? It is a close second to being thrown on a mound of red ants with your body dipped in honey......ahhhhh....what a pleasure.

As a matter of comparison and for those that have a new K bike, the whole tranny can be pulled out of one side of the bike and the clutch can be changed in a jiffy......hey I love to change oil......

This post is not an attempt to demean any writen material or bike ownership. I had the pleasure of owning a nice and dear R, unfortunately we can't go on believing that a 60 year old design is still, with some modern updates is the leading edge of technology.

Boxermainia - I have no illusions that the bike I love is leading edge technology. But then, I ain't the latest model either and I can still perform pretty well when called upon!

What a lovely topic, Mike. An engineering design thread! I'll be surprised if I manage to beat Ves in posting a message.

The parallel here is Porsche with its 50 year old design. It still hold its head very high in the supercar league and with some justification.

Both manufacturers have stuck with a tried and tested engineering design which works. Both designs are still managing to survive because enough people are voteing with their wallets and are still buying them.

The only controversial thing I would have to say is that I'm a perky-tit man. I prefer the concept of a 90 v twin over the 180.

Long live the BMW engineering concept (and the Guzzi!)

Ride safely,

Rog

6758

Did someone call me...? I thought I heard my name...

In addition to the Rockster I own a CBR1000RR. Lack of riding comfort aside, it represents the pinnacle of what a street motorcycle is meant to do... go really fast from point to point regardless of the line that connects those two points. It has about 160 hp at the crank, very smooth, and more suspension adjustments than most people will ever figure out. It's a tool... a scalpel that allows you to dissect any road. When I ride it, I can look straight ahead and I don't see anything but the road... I just feel it beneath me, responding to my every command. It is cold, efficient, and without character. And it is like every other crotch rocket out there. Put them next to each other, take off the insignias, and you'll have to look closely to tell the difference between them.

On the other hand, when you look at a BMW boxer, there is no mistaking it even a block away. That's part of the attraction. By sticking to their design, whether through indifference, stubbornness, laziness, or conservativeness, they now have something that is very unique. The first time I saw my R850R sitting in a front yard with a For Sale sign on it, it just struck me. It didn't look like anything I had seen before, and I had to turn around to get another look. There's just something about the lines that's pleasing to the eyes. Maybe it's the big jugs, or the wide tank that comes to a narrow waist. I can literally just sit there and look at the bike, like it's some sort of industrial art... the more you look the more you see.

But then, when you look beyond the appearance, you find that it's mechanical design and function are just as unique as the appearance. The anti dive front end, the unique shaft drive design, the oil cooling, it uses the engine as a stressed member for mounting the suspension, the unique turn signal layout, the ease with which maintenance can be done.

So, I find that it's esthetically and technologically pleasing. I can appreciate it at multiple levels... it's like an ogre (some would say it's as ugly as an ogre)... it has layers... The final layer is how it feels under you as you're railing through the curves. And it feels good and solid.

As for why it handles as well as it does. My guess is this. When a gyroscope is rotating, it resists being rotated perpendicular to it's rotation of axis. That's why a rotating wheel is inherently stable. It does not want to fall over. Any rotating part is a gyroscope. Any gyroscope rotating front to back will resist being tilted side to side (works against the motorcycle leaning). Most engines and gears rotate front to back so they resist being tilted side to side. The BMW crank and gears rotate side to side, so they do not generate any angular momentum that resists side to side motion. I don't know how significant that is, but that's my story and I'm sticking with it.

boxermania wrote: unfortunately we can't go on believing that a 60 year old design is still, with some modern updates, the leading edge of technology.

I fully agree, to my current understanding.

But, as a balance, I make my living at the bleeding edge of technology. There is something to be said for the tried and true. Subject to the goal that you are seeking, of course.

(This is me, coming squarely from the "what the hell do I know" category)

-Kyle

To me, the boxer-powered BMW roadster is a thing of beauty. It fuflills its intended purpose as few other mechanical devices do. Each and every variation of the Roadster is a classic.

mac

Ves wrote:Did someone call me...? I thought I heard my name...

In addition to the Rockster I own a CBR1000RR. Lack of riding comfort aside, it represents the pinnacle of what a street motorcycle is meant to do...

Sorry Ves, but the Fireblade is NOT a "designed specifically for the road" motorcycle. It's a converted racebike (like all SuperSports machines: softer suspension settings, a few tweaks to chassis to make it managable, softer engine tune and thicker seat padding - well, on most of them....). It's designed to do around a supersmooth race track at race-winning speeds. Down your average, cheaply tarmaced non-trunk road it'll bounce all over the place and be highly uncomfortable.

The BMWs are designed purely for the road, and hence excel on it.

Just to make my comments perfectly clear.....I have been passionate with IC engines since I was a kid and have been fortunate to continue my involvement, both as a hobby and professionally as I matured.

The Boxer engine was a brilliant design when conceived, many years ago. Simple design, aluminum castings, short, strong crank, 180 degree firing, air cooled, few moving parts, automotive type clutch and later, automotive charging system. What a blend of technologies !!

Of course with every design there are compromises, in this case:
1) Temperature diferential from the front to the rear of the cylinder, ie, thermal expansion potentially affecting the circumference (roundness) of the cylinder. This in itself places an additional burden on the sealing job required by the rings.
2) Horizontal cylinders retain sugnificantly more oil (due to the fact that they don't have gravity working with them) than inclined or vertical cylinders, once again burdening the ring's job.
3)The automotive clutch has the benefits of being dry, but the tranny/engine being an structural part of the package the clutch is not easy to access and change.
Likewise, the clutch diameter is affected by the available room, in this case 6.5" which if abused will wear out fairly quickly.

This are just a few of the design elements and no, they are not design killing elements but one should be aware of them to minimize problems during ownership.

Last but not least, add on the problems that arise as a result of what I will refer to as "engineering designs to meet regulatory constraints"

These in itself involve the frollowing:
Surging - Itself the attempt by the OEM to lean out the A/F ratio at steady state conditions so as to meet with: adequate mileage, emission regulations and corporate image.
Excessive oil consumption while new - The result of the required accomodation of rings to cylinder surface to keep in check all of the original design shortcomings. (See above)
Lastly - All the other nagging failures experienced by a limited number of owners, primarily as a result of improper machining or assembly or poor design. Such as the clutch spline failures, diferential bearing failure and grabby servo assisted brakes. These failures, being of limited nature it is best for the factory to plead ignorance and take care of the squeaky wheel at the dealer level.

This is not a frontal attack of the brand, just explaining the design to learn what to look. I owned both a K75 and an R1150R. These bikes, once you understood their shortcomings, were two of the best bikes that I have ever owned.