Shaking forces in wins

[JCsman]

There has been some discussion on V-angles and which are superior lately. Of course there are no "right" answers, but for the math freaks and engineers in the crowd (good graphics too - just scroll past the math) here's the inside scoop..

http://www.dinamoto.it/DINAMOTO/on-line%20papers/twin%20motors/twin.html

I must be getting old. At one point in my life I'd have dove into the math here until I "understood" it. Maybe later. But the graphics are pretty illustrative.

Boxer fans might note that the perfect balance shown is not the whole truth since the cylinders are offset when viewed from above.
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Now, you guys can further my education. Here's a thought I posed a long time ago on another board. But I didn't explain it at all well (based on the responses). Imagine a boxer engine with "knife and fork" connecting rod set up. Like the H-D, but a WIDE fork and three crank throws instead of one. The "two" con rods on one side tie together to a single piston.
UPDATE: Dang - I tried a "graphic" using lines off the keyboard ( _ & |) that didn't work. Looks OK before I save, then a mess. And I can't upload a paint file......... Hope my words are clear this time.


Of course the engine is:
- longer
- more complex
- has a heavy set of connecting rods (that fork would be a bear of a con rod to build)
- More expensive

But it should be as close as possible to balanced primary and secondary forces. That avoids complex devices to minimize vibration and should allow relatively high revs.

With today's counter-balancers, and the complexity, I suspect this is an answer to a question better left unasked. Still I await wiser heads telling me just why this is so obviously the dumbest thought since the mono wheel.

[Deans BMW]

Not a dumb thought at all. One of the goals in performance is to lighten the recprocating mass, allows a safer and more attainable hi RPM.

I have had the opportunity to ride a Boxer Beemer with Titanium rods and lightened pistons, all balanced and with lightened flywheel as well, to put it mildly, simply amazing in its smoothness and responsiveness.

[Wild Will]

I've owned plenty of V twins, but they were all 90 degree. Math aside, they were all smooth, unlike the vertical twins of my yout', and were smoother than my 1100 BMW flat twin. The 1200 flat twin has a counterbalancer, and is as smooth as the KTM twin with counterbalancer. The only HD I rode was not smooth, but it wasn't hung by "Heim" joints isolating the vibes from the frame.

My favorite engine configuration is, by far, a 90 degree vee twin, as in Honda Superhawk, Suzuki SV, Ducati either air or liquid cooled, and the latest BMW flat twin. I ride my 1200 GS regularly at over 7K RPM, and it's very smooth.

I've read, although not felt (although I've ridden several), that the F800 is vibey at higher RPM's. I'd definitely test ride a new Interceptor if I was in the market; all I want now is a pristine RZ 350 and a 250 Metralla!

[NoRRmad]

The "knife and fork" con-rod setup requires that the pistons both move in the same direction, which would make vibes like a big single. You could reduce the small vibration produced by the piston offset by having two con-rods on one piston, and two opposing crank throws for that piston on each side of the crank throw for the other piston. The pistons could then be coincentric, but you'd have to balance two small con-rods against a single one.

[JCsman]

The "knife and fork" con-rod setup requires that the pistons both move in the same direction...

NoRRmad,
Your response reflects the same misunderstanding I had before. My inability to articulate, I suppose. A drawing, if I could get one to post, might have helped.

The H-D knife and fork with a single pin crank would indeed act like a huge single.

I tried to make my difference clear with references to "wide" fork and three throws. Sorry if I'm unable to make the verbal picture clear.

[JCsman]

This crude drawing may make it clearer. The heavy line is the crankshaft, the boxes the pistons, the finer lines the rods. (In hindsight I should have made the single/knife rod a VERY thick line!)

Dean is, of course, correct. There would be heavy reciprocation mass. But if weights were equalized it should be in balance.

http://www.motorcyclistcafe.com/forums/picture.php?albumid=3&pictureid=62

[Sir Limpsalot]

It would, indeed be in balance. The "standard" boxer layout is also in balance apart from the "rocking couple" caused by the offset which your solution seeks to address. I suspect that as the effect of the rocking couple is quite small the improvement would not be worth the effort.

Will, my two favourite 90degree Vee twins are this one..

http://www.theshop.co.nz/TBIKE/items/images/b6620_7.jpg

http://www.bellacorse.com/images/bcz002a.jpg

And this one..

http://i296.photobucket.com/albums/mm184/andy_d17/nec2008209.jpg

Cheers,
Si.

[JCsman]

I suspect that as the effect of the rocking couple is quite small the improvement would not be worth the effort.
Cheers,
Si.

Yeppers, Dean convinced me. Might work as an improvement on Dave's washing machine though.

[DarthRider]

Yeppers, Dean convinced me. Might work as an improvement on Dave's washing machine though.

What do you mean?
How could you improve on this?

http://r1150r.smugmug.com/photos/44315759_pkWrP-O.jpg

If it's good enough for the Germans, and to wash our clothes, it's OK with me...BMWs & Maytags forever!

[Deans BMW]

Bill, you left the piston rings off your drawing.......................

[JCsman]

Bill, you left the piston rings off your drawing.......................

That damn CAD tech is FIRED! :):):)

My old drafting* professor would be stunned at the quality of my work!

* Yes, for you kids out there, I mean drafting with lead pencils.... man how times have changed. Now where did I put my slide rule?

[Deans BMW]

Bill in one of my former lives, I spent many a day on the drafting table, also had a "Lofting" table.

The lofting table was for full size Aerostar Aircraft working drawings, I actually enjoyed it.

[panthercity]

What do you mean?
How could you improve on this?

http://r1150r.smugmug.com/photos/44315759_pkWrP-O.jpg

Turn it into a benchracer with a Bankee pipe?

http://www.panthercity.net/bnchraces.jpg

[DarthRider]

Turn it into a benchracer with a Bankee pipe?

http://www.panthercity.net/bnchraces.jpg

I have the motor Bob...you have the pipe?

[panthercity]

Not any more. Last I saw it was still down on the Lancaster Dyno. Oh, and I trashed the bars and the number plates on later projects.