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Buzzy Beemers?

PostPosted: Mon Jul 22, 2013 1:27 pm
by Mike James
Hiya,

I've finally been able to take some multi-hour trips this summer with the '07 F800ST that I bought in the fall. I am dealing with the handlebar vibration now and go most of the problem licked -- at least my hands aren't falling asleep any more. I added heavier bar ends, and changed my posture and gripping style.

In my research on this problem, I have learned that parallel twins are inherently "vibracious." Since I'm thinking about upgrading to a newer bike in the semi-near future, I want to make sure I'm not looking at buzzy bikes.

Are there BMW models and/or engine configurations that are less prone to engine vibration?

Is your bike especially buzzy or not buzzy? What model do you have?

Thanks!

Mike

Re: Buzzy Beemers?

PostPosted: Sat Jul 27, 2013 6:37 pm
by Mike James
My K75s is a lot less vibratory, but I don't know why exactly.

Three cylinders have a higher harmonic than two cylinders at the same RPM?

Re: Buzzy Beemers?

PostPosted: Sat Jul 27, 2013 8:32 pm
by Slider
Buzzy Beemers, wasn't he Hopalong Cassidy's side kick?

Re: Buzzy Beemers?

PostPosted: Mon Jul 29, 2013 11:33 pm
by Mike James
Bump.

Re: Buzzy Beemers?

PostPosted: Tue Jul 30, 2013 11:07 am
by Unity
Engines with multiples of 3 cylinders are inherently smoother. There might be better explanations on the Web, but here's what I found quickly:

AutoZine Technical School wrote:While single-cylinder engine fires once every 2 revolutions, twin-cylinder engine fires once every revolution, 3-cylinder fires once every 720 / 3 = 240° crank angle, 4-cylinder fires once every 180° (half a revolution) .... 12-cylinder engine fires once every just 60° crank angle. Obviously, the more cylinders the engine has, the smoother the power delivery becomes.

This explain why we prefer V12 engines than in-line 6, although both of them achieve near perfect internal balance.
. . .

Inline 3-cylinder engines

As the engine fires once every 240° crankshaft angle (720° / 3 = 240°), the crankshaft design is as shown in the below picture. (Firing order is: 1-3-2)

It seems that no matter how the crankshaft rotate, the combined center of gravity of all 3 pistons and con-rods will remain at the same location, hence no vibration generated. By mathematical analysis, you can also find there is no forces generated in vertical direction as well as transverse direction. (actually, I really performed such calculations) So why did we hear that 3-cylinder engine need balancer shaft ?

In fact, the calculation is wrong because it assumes the engine is one point, thus the forces of all 3 cylinders act on this single point and result in complete cancellation. In reality, the forces act on 3 different locations on the crankshaft, thus instead of canceling one another, they make the crankshaft vibrating end to end.

Image

Don’t understand? look at the above picture, the side view of the engine. Piston 1 is at the top now and is going downward, thus generates an upward force to the left end of the crankshaft. Piston 2 is also going downward, thus generates an upward force to the middle of the crankshaft. Piston 3 is going upward, thus generate a downward force to the right end of crankshaft. As the engine’s center of gravity locates in cylinder 2, you can see forces from piston 1 push the left end of the engine upward while forces from piston 3 push the right end of the engine downward; After 180° rotation, the situation will be completely reversed - downward force at left and upward force at the right. In other words, this is an end-to-end vibration with respect to the center in cylinder 2.
(Site is here.)

--John
(Next time you're at an aircraft museum, count the cylinders on a radial engine.)

Re: Buzzy Beemers?

PostPosted: Wed Jul 31, 2013 9:03 pm
by Mike James
Thanks for the insight John.

It would seem that the number of cylinders is only part of the equation as to what makes a Beemer buzzy.

Boxers (flat twins) are two cylinders as well, but I don't hear much about vibration being an issue. Or do I hear wrong?

Do you need to go to a 4-cylinder K bike before you get a smooth ride at highway speeds?

The reason I'm asking these questions because I'm trying to go with a group from Frederick to Niagara Falls in September, and I know my F800ST will be a rough ride after the first few hours. :(

Thanks,

Mike

Re: Buzzy Beemers?

PostPosted: Wed Jul 31, 2013 10:51 pm
by Unity
I'll leave the discussion to the F650/F800 riders now.

--John
(Yes, boxer twins have some vibration too. On long rides last summer I started having trouble with substantial loss of feeling and dexterity in the thumb and first 2 fingers right hand. The hand specialist I'm seeing doesn't want to fix my vibration-induced carpal tunnel syndrome surgically, not yet, so I'm able to ride now thanks to occasional corticosteroid shots. Better living through chemistry.)

Re: Buzzy Beemers?

PostPosted: Thu Aug 01, 2013 12:51 am
by Mike James
I'd like to ask the RxxxxRT riders if they get a much engine-related vibration at highway speeds.

Thanks.

Re: Buzzy Beemers?

PostPosted: Thu Aug 01, 2013 2:38 pm
by Blixa
Could a throttle lock help with the vibration? That way you won't have to grip the throttle as tightly, which may provide some relief on a long trip.

Re: Buzzy Beemers?

PostPosted: Thu Aug 01, 2013 4:36 pm
by Chiba
Mike James wrote:Boxers (flat twins) are two cylinders as well, but I don't hear much about vibration being an issue. Or do I hear wrong?

I don't know about other people, but my hands get sore & numb from vibration after many hours in the saddle on my R1200GS. On my K1200RS (4-cylinder), I don't have this problem.

Re: Buzzy Beemers?

PostPosted: Thu Aug 01, 2013 5:22 pm
by BKling
R1150RT. I don't find my RT to be buzzy, but I do use a throttle lock to relax a bit when I can. I have also found that prior to a tuneup they can vibrate a bit more, I am not sure that would apply to an F series.

Could tire balance contribute to your problem?

Re: Buzzy Beemers?

PostPosted: Thu Aug 01, 2013 10:14 pm
by Mike James
Could a throttle lock help with the vibration?


I've got one and it helps keep my hands loose on the grip. I do get some weird/unsafe surging when I bump it accidentally though. I wish real cruise control were affordable!

Could tire balance contribute to your problem?


It's a possibility, but this is a high frequency buzz - maybe in the 50-60Hz range. I'll play with motor RPMs vs. actual speed om my commute in tomorrow and see if there's any funny business

It's funny - I've been looking at the 4-cylinder forums: K-Bikes, Concourses, etc. and they all complain about buzz too. :(

Mike

Re: Buzzy Beemers?

PostPosted: Fri Aug 02, 2013 11:27 am
by sati8d
Also try the short version of Cramp Buster for $10 - it works because you're not gripping the throttle, but pressing it with the meaty part of your palm - it's made a HUGE diff for me on my GS Adv with knobby Heidies and I commute too. I also have the Kaoko Throttle lock - really helps on longer trips, not for commuting.
There are also wraps you can beef up your grip - they're made of a neoprene - pretty cool, was going there, but the Cramp Buster solved it for me.

Re: Buzzy Beemers?

PostPosted: Fri Aug 02, 2013 11:49 am
by Mike James
No funny business with tire vibration. It all comes down to engine RPM.

Also try the short version of Cramp Buster for $10

Have had that for a while and they do help a lot. Gel gloves help a bit too. Posture and relaxing the grip is the biggest fix.

I realized this morning that my Heli riser is probably amplifying the vibration since it puts the grips further away from the frame. I would take it off to check but it was such a pain in the @$$ to put on! Also taking it off would defeat the purpose, since I'd be putting more weight on the grips.

I am coming to the conclusion that all bikes buzz -- some more than others. The 3 and 4 cylinder bikes are better but not perfect.

I'm considering the purchase of a 4-cyl 2013 Concours - can't afford the BMW equivalent (the Costco-Kawi deal is quite enticing) --- or a Honda ST1300. Also will be trying two rented V-Twin Harleys this weekend to see what they are like. One with and one without the motor shock mounts.

Have a good weekend everybody!

Mike

Re: Buzzy Beemers?

PostPosted: Sat Aug 03, 2013 4:30 pm
by jpsmith
Everything has a resonant frequency dependent on the velocity and displacement of the excitation(s). It could even be that separate motions are combining and amplifying. Eliminating one would neutralize the other.
My Goldwing has a couple of combinations of throttle, load, and speed that fuzzes the mirror or a peg. My R1200RT had a couple of sweet spots too. You just need to ride around them as best that you can. Check your bike over and keep a check that all of your bolts are tight and that the engine and frame vibration isolators are not worn out. Have fun, ride safe. Jim