Strange R1250GS engine noise. - Page 22 - BMW R1200GS Forum : R1200 GS Forums
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post #211 of 220 (permalink) Old 11-Sep-2019, 01:36 AM (275)
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Originally Posted by Slijkmoto View Post
The enigma just grew bigger ; my dealer just reported to me that he'd exchanged the throttle bodies from his quiet R1250GS with those of his noisy R1250R , with the following results :

- the QUIET GS remained as quiet as before
- the NOISY R remained as noisy as before (but with a slightly different kind of noise).

CONCLUSION : the throttle bodies don't appear to be the (only) cause of the resonance noise...

Now I really dont know anymore...
It has to be something to do with airflow, it has been horribly wet here the last few days and riding in to work this morning in torrential rain the noise is hardly discernible, I am guessing it is the denser air making a difference.

We know for sure from your video that there is an oscillation taking place in the throttle butterfly and in my case I have just got lucky being able to tune it out to a degree by moving the butterfly to a different angle in relation to the intake port.

It is nothing to do with the shape of the airbox or air filter or intake hose shape up to the throttle body itself as these are all removed in your video.

Your dealers experiment also rules out the quality of the actuators themselves so it has to be something to do with the inlet tract of the cylinder head or the inlet valves themselves.

Modern casting techniques would rule out surface finish to the intact tract I should have thought, some of the old cylinder heads I have worked on had very rough surface finishes. But could it be related in some way to the casting of the heads? something has to be disturbing the airflow on our bikes and causing the flutter.

One other possibility I guess is a firmware/sensor issue, some form of feedback causing the butterfly to over correct its movement
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post #212 of 220 (permalink) Old 11-Sep-2019, 03:51 PM (869)
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Hi all,

Is there any way to put a screen upstream off the valve? What I'd like to do is change the flow profile of the air. It could be that the air hasn't "settled down" and is all chaotic, thus causing the noise.

Kam
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post #213 of 220 (permalink) Old 11-Sep-2019, 11:40 PM (194)
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Quote:
Originally Posted by Kam View Post
Hi all,

Is there any way to put a screen upstream off the valve? What I'd like to do is change the flow profile of the air. It could be that the air hasn't "settled down" and is all chaotic, thus causing the noise.

Kam
That was my initial thought, I had in mind designing and 3D printing a ring with a small protrusion into the airflow that would fit on top of the throttle body. This would disturb the airflow and hopefully alter the resonance.

The problem is warranty though, the clips used to hold the rubber hoses in place look like one time only use so unless these are easy enough to purchase and dont require a specialist tool to fit this is a non starter.
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post #214 of 220 (permalink) Old 12-Sep-2019, 03:14 AM (343)
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I think the clamps are easy to purchase but require a special tool , provided to the BMW dealers.
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post #215 of 220 (permalink) Old 12-Sep-2019, 01:00 PM (750) Thread Starter
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R1250GS.
Made by BMW.
Developed by owners.
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post #216 of 220 (permalink) Old 12-Sep-2019, 03:53 PM (870)
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Thank you Slijkmoto for the video file showing the open top of the throttle body with the sound coming from the butterfly valve (if I'm describing things correctly). I note that the sound significantly reduces when the person puts their thumb on the valve, but not entirely disappears.

Now it gets interesting, because, at about 800 km on the clock, and for the past week or so, I am able to hear a sound relatively close to the sound in the video. I experience this sound on easy-moderate acceleration from standstill in first gear. With harder acceleration is isn't apparent, but I think that that is due to the higher general engine noise masking it. If I accelerate very gradually, it isn't apparent. The volume is what I would call low - I can't hear it with full face helmet's visor closed and I'm not wearing earplugs. Can't hear it once I'm moving with any speed at all, maybe due to the usual noise coming up from the front wheel and air passing the triple clamp, etc.

Now, it's very similar, but I can distinguish it from another, "second" sound that I hear on acceleration (any acceleration effort, low, medium, hard), which sounds very convincingly to me like the fluttering of the butterfly valves that one would more/less expect to hear on any acceleration - this sound is close in musical pitch (freq.) to the one above and which I hear in your video, but this "second" sound seems normal to me, is also (for me) pretty quiet and seems like the normal sound of the moving butterfly valve on acceleration as the engine pulls air.

What grabbed me as I listened to your video is that the sound there seems to me, to be similar to the fluttering of the butterfly valve on normal acceleration as the engine pulls air, but this sound in the video has a more metallic nature to it, more harshness, which for the past week, has been how I myself have characterised the sound that I described first above - "that sounds a little like the "normal" butterfly valve air movement sound, pitch is close if not the same, but this sound has a more metallic nature to it - maybe like two pieces of metal being rubbed together - like a pan shuddering gently against the muffler, or something like that".

So, I'm not sure if I'm hearing the same "abnormal" sound as you and Maturerider have been suffering. I can say categorically that this harsher metallic sound that I'm hearing, not dissimilar to your video, is certainly quite low and so far (fingers crossed) hasn't changed/increased, hasn't got to the high volume that the two of you have described sadly. If I accelerate gently, (pretty gently) it doesn't seem to occur, but I still always hear the gentle, airy, fluttering sound of the butterfly valves. I interpret that sound as normal.

so to close, two questions:

1) the sound that the two of you are hearing is/has become definitely loud and impossible to ignore, right? someone said it had induced tinnitus? That's what I think you both said way back.

2) am I right in describing the more normal sound that I'm hearing on acceleration to be the normal airy-fluttervalve sort of sound from the butterfly valves moving normally as the engine pulls air, normally? that is, on acceleration from standstill, is it indeed normal to hear a low volume fluttering kind of air sound? sort of a "whiffling" sound? can I attribute that sound to fluttering of the butterfly valves? do butterfly valves indeed flutter normally as air is pulled into the cylinder? or do they just open and stay fixed in place?

I can definitely distinguish these two sounds, rather related, but the one that I don't attribute to normal functioning of throttle bodies so well, seems more metallic, slightly rougher/harsher, and more like two pieces of metal being rubbed together, or like a soft sound coming from a muffler pan or similar, shuddering/vibrating when you accelerate. The butterfly valve sound that I think that I'm also hearing seems more obviously airy, it seems the obvious sound that a throttle body should make as air passed through it and through a fluttering valve . . .

?

thanks for reading this, guys!
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post #217 of 220 (permalink) Old 12-Sep-2019, 04:37 PM (901)
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Slijkmoto, you mention earlier on that you made a recording yourself? Do you still have this, would it be possible to forward that to me? Rereading your posts along with Maturerider, your sounds are very loud, and Maturerider described it as a rattle/knock etc. . . . not a fluttering, shuddering/whimpering sort of sound that I'm hearing.
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post #218 of 220 (permalink) Old Yesterday, 12:40 AM (236)
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The next two days I shall be driving my car north to Belgium and I’ ll check the availability of my own video recording when I am home.
However the strange noise I am experiencing doesn’t cause any tinnitus, but has a pitch and frequency that cannot be muffled neither by my quiet helmet, nor by my 33DB foam earplugs that do muffle all other typical GS engine rattles.

Last edited by Slijkmoto; Yesterday at 01:21 PM (764).
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post #219 of 220 (permalink) Old Yesterday, 06:29 AM (479)
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'05 1200 GS
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post #220 of 220 (permalink) Old Yesterday, 12:26 PM (726) Thread Starter
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Love it! Very funny.

That's me in the video. Although with all the noise I now look a lot older.
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