30 August 2010

Engine Vibrations

I know, the R1200GS is a twin. It's a twin with two big combustion chambers. It will vibrate. It does vibrate. There is just no way around.

But, the amount of vibration, the frequency, and how it feels matters.

When I test rode a bike from SJ BMW I felt vibrations but that didn't bother me. I did about 150 miles on a single day with the demo bike I had over a weekend - didn't want to push the generosity all too much - and I had no problems at all.

When I got my own one, a 2010 R1200GS, it had different vibrations than the demo model. More intrusive. More annoying. I got tingling hands and feet after even short rides. It was so much that it became painful after a few days. I really didn't know what to do, the only thing I could do was to wait, break it in, have the throttle bodies sync'ed (remember, big opposed twin with throttle cables) during the 600 mile service and see how far that goes.

The vibrations smoothed out around the 300 mile mark. I didn't know why, and I was pretty happy. I could still feel my hands and feet a bit disturbed after longer rides, but it wasn't a problem anymore. Then the service was done and it was even better.

At around 800 miles something happened again, the vibrations came back. Not gradually, not over time, not slow. I was on my commute from home to work, off-ramp from 280 in Cupertino, just switched gears down into 4th and bang it was vibrating again. Now, that was weird. I didn't know what happened, but from one second to the next, the engine vibration changed, I think I heard something, but can't be sure as I always wear earplugs while riding. Still, the vibrations were back and I had no idea why.

On Saturday I talked to Tom at SJ BMW whether he had heard of that before. Wanted to talk to Chris, too, but he was too busy preparing bikes for Bonneville racing and I really didn't want to bother him with my "vibration problem" which could have been just me.

So, later that day, I started thinking about the whole situation and what I did when the vibrations slowly went away and also what I had done before they came back and there was only one thing: I used different fuel.

When I got the bike initially, Tom told me, they use 89 AKI rated fuel when filling the bike. This is also what BMW recommends as the minimum rating. I immediately used premium (91 AKI). Don't know why, maybe I thought I do some good for the bike. Now, when I got it back from the 600 mile service, I wanted to find out where my decreased gas mileage was coming from and filled the tank again with 89 AKI rated gas. Here are the fill ups:
  1. 0 miles, 89 AKI
  2. 144 miles, 91 AKI (6.13l / 100km; mileage from last fill)
  3. 279 miles, 91 AKI (5.12l / 100km)
  4. 452 miles, 91 AKI (5.4l / 100km)
  5. 578 miles, 91 AKI (5.9l / 100km)
  6. 741 miles, 89 AKI (5.8l / 100km)
  7. 932 miles, 91 AKI (5.5l / 100km)
So, it was vibrating when I got it. It smoothed out around the 300 to 350 miles mark. It was okay until 800 miles or so, I don't recall the exact number, but it was around 800 to 820 when the situation mentioned above happened and it started vibrating again from one second to the next while riding. It seems to be smoothing out again. Slight tingle in hands and feet today at the 1040 miles mark.

So far this is just a guess. I haven't reproduced it enough and I don't know whether I want to when it smoothes out again as it really involves some pain - believe it or not. But for the sake of science I might run 91 rated gas for a while, at least two or three fill ups, then maybe switch back to 89 for one and see whether the vibrations come back. It takes some time doing all this as I'll not be riding that much over the next couple months, but still, I'm curious myself and want to find the reason for the vibration. My complete non-expert theory right now is that the anti-knock sensor in the bike together with whatever the injection system / computer does to prevent knocking or ringing (basically to prevent early ignition) puts it into a state where it vibrates more. This is a totally wild guess and completely non-technical, just gut feeling and enough knowledge of what the bike does to do some stupid guessing.

But I have time and have the chance of trying it out. So I probably will. I'll report how it goes.

6 comments:

  1. Understand from local dealer that new 2010 R1200 engine basically slightly higer vibrating tendency due its DOHC system than SOHC earler version. But it has more power ^^.

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  2. It is possible but it doesn't explain the significant differences I'm experiencing on a single engine ...

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  3. Yes you right!! Hope you figure it out sooner or later or get used to it ^^;

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  4. Me too, absolutely! But I'm determined to find out ...

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  5. Guido:

    There's only ONE solution to your dilemna. I have to come down and ride the bike back to British Columbia and give it rigourous testing in the mountains at different altitudes using a combination of different octane ratings at differing speeds at high RPM, also to factor in the differences in gas blended at different stations. It will take a while but as you are not riding anyway makes sense to get an expert opinion. I will return the bike in early spring along with my conclusions.

    You can thank me later . . .

    bob
    www.wetcoastscootin.blogspot.com

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  6. Yeah, of course ... ;-)

    Can I say thank you right now for the nice and self-sacrificing offer? You would do this all for the sake of science and my well being. Aaaaah!

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