Wierd mystery pulsing/whirring sound.

Malcolm Leick

Registered user
Joined
Jan 16, 2009
Messages
276
Reaction score
0
Location
Bamford (The Peak District) , England
This seems to be my week for posting new threads!

I noticed a strange sound on the bike today for the first time. When the engine is under load, i.e. the throttle is active, there is a strange whiring sound, like something metalic rubbing, which pulses at about 2 cycles per second. The speed of the pulsing increases the faster I go, but disapears completely if I shut off the gas. The bike has 43,000 miles on the clock and I have never heard this before. Engine performance is not affected.

Any thoughts? F650 GS twin BTW.

Is it the sound of something expensive breaking???

A few times in the recent past I have also had a loud high pitched metalic screeching when accelerating from standstill. Usually the bike stalls. There is no routine slippage on the clutch and the adjustment is fine...so again I am mystified. It's happened 2 or 3 times in the last year and afterwards, everything is as normal.

Any clues?
 
Malcolm Leick said:
This seems to be my week for posting new threads!

I noticed a strange sound on the bike today for the first time. When the engine is under load, i.e. the throttle is active, there is a strange whiring sound, like something metalic rubbing, which pulses at about 2 cycles per second. The speed of the pulsing increases the faster I go, but disapears completely if I shut off the gas. The bike has 43,000 miles on the clock and I have never heard this before. Engine performance is not affected.

Any thoughts? F650 GS twin BTW.

Is it the sound of something expensive breaking???

A few times in the recent past I have also had a loud high pitched metalic screeching when accelerating from standstill. Usually the bike stalls. There is no routine slippage on the clutch and the adjustment is fine...so again I am mystified. It's happened 2 or 3 times in the last year and afterwards, everything is as normal.

Any clues?
Click to expand...
I had a similar cyclic sound it turned out to be the rear wheel bearings.
 
You can get a similar low frequency sound by the chain not being adjusted correctly, as it sets up an oscillation on the bottom of the chain when under load ( acceleration), and this gets transmitted through both the crown wheel and the pinion. It disappears on decelaration or no load because the bottom of the chain is then under tension.

This noise can also be exacerbated if the chain isn't lubricated properly.

As far as the screaching is concerned, have you checked the state of the front pinion cog and it's teeth?
 
JWFr said:
You can get a similar low frequency sound by the chain not being adjusted correctly, as it sets up an oscillation on the bottom of the chain when under load ( acceleration), and this gets transmitted through both the crown wheel and the pinion. It disappears on decelaration or no load because the bottom of the chain is then under tension.

This noise can also be exacerbated if the chain isn't lubricated properly.

As far as the screaching is concerned, have you checked the state of the front pinion cog and it's teeth?
Click to expand...

This sounds favourite to me - if it sounds mechanical it usually is - and if the chain and sprockets are worn along with a loose chain you're gonna get that sort of trouble...... and its dangerous!
43000 miles - when was the last chain and sprocket change - if you're not using an oiler it should be on atleast its 3rd set and probably due a 4th?

Steve
 
JWFr said:
You can get a similar low frequency sound by the chain not being adjusted correctly, as it sets up an oscillation on the bottom of the chain when under load ( acceleration), and this gets transmitted through both the crown wheel and the pinion. It disappears on decelaration or no load because the bottom of the chain is then under tension.

This noise can also be exacerbated if the chain isn't lubricated properly.

As far as the screaching is concerned, have you checked the state of the front pinion cog and it's teeth?
Click to expand...


My apologies , I 'm having a bad hair day today! I don't mean crown wheels or pinions, I mean bl**dy sprockets. I've been stuck inside a complex sterring box for the last week, and I can't get the damn things off my mind.
 
As ever, thanks to everyone for your suggestions.

The chain is actually pretty tight as the tyres were changed last Saturday. Come to think of it, that's how long it has been making the noise! I thought it was maybe a little overtight.

I have a Scottoiler and my chains do seem to last a long time, about 25,000 on the first OEM one. I do have a spare front sprocket so I may put that on and see if it makes a difference.

I'm still owed a chain by BMW as I have never had the recall job done, and Rainbow said they would do it whenever I was ready. Do they give you a new sprocket at the same time? I'm running on a gold DID chain at the mo, but I guess they will only fit the standard OEM chain when they replace it.

I was worried it might be something going belly up in the gearbox or engine, so if it is a chain/sprocket problem I will be mightily relieved.
 
If the chain is too tight then your output bearing inside the gearbox might be knackered,,,,be careful how you precede from here...
If the shop has tightened the chain too much and has knackered the output bearing then a full strip of the gearbox is needed..
I have tightened my own chain too much but only went 20 odd miles before it was correctly adjusted, luckily no damage occurred...
It all depends on how tight it is with your weight on the bike, and how many miles you have done....
Lets just hope it was just tight and not stupid tight, with your weight on the bike there should be at least 20mm of play, better a slightly loose chain than a tight one...
Good luck.
 
Malcolm Leick said:
As ever, thanks to everyone for your suggestions.

The chain is actually pretty tight as the tyres were changed last Saturday. Come to think of it, that's how long it has been making the noise! I thought it was maybe a little overtight.

I have a Scottoiler and my chains do seem to last a long time, about 25,000 on the first OEM one. I do have a spare front sprocket so I may put that on and see if it makes a difference.

I'm still owed a chain by BMW as I have never had the recall job done, and Rainbow said they would do it whenever I was ready. Do they give you a new sprocket at the same time? I'm running on a gold DID chain at the mo, but I guess they will only fit the standard OEM chain when they replace it.

I was worried it might be something going belly up in the gearbox or engine, so if it is a chain/sprocket problem I will be mightily relieved.
Click to expand...

The chain recall replaced both sprockets and updated chain, I had my 800 replaced at 8K, now done 32K with Scottoiler, and ready for replacement soon :)
 
No - on the side stand.

Swapped the front sprocket for a 16T ( I had a 17T on it) and I think I see the problem. The chain has good play most of the way round - but at a couple of points it goes much tighter.

On the centre stand, in second gear, this seems to set up a sort of oscillating wave through the chain as the wheel spins. On the road, the pulsing noise is still there.

Not sure what to do now as if I tighten it any further it will seize up, and if I slacken it, it will be too loose for most of the chain revolution.

I guess it's time for a new chain and sprockets?
 
A chain be it on the side stand or centre stand wont give you an accurate reading.
To check a chain, sit on the bike and feel the tension of the chain then move the bike forward about two inches, bend down and feel the chain again..so on and so on...
I bet ya the chain is too tight, and with tight spots on the chain that might be where the pulsing is coming from...
With a chain always have it too loose than too tight..Your output bearings will thank you for it...
Also, have you thought about your rear wheel bearings, especially the brake side, as this side only has one set of bearings where as the sprocket side has two sets of bearings..Good luck...
Also have you checked your rear wheel/ chain alignment, that could make a funny noise if the alignment is way out.......Take a very close look at your sprocket teeth, front and back and see if there is any witness marks telling you if the alignment is out......Tosh
PS, i'm no expert, this is only what I have learned from fellow tossers on here
 
A chain will be at its tightest when the front and rear sprocket centres are in line with the swing arm pivot.
Use a strap (or volunteer weight) to get all three in line and then check chain tightness. (Obviously wont need much play - but you'll be able to tell if it's over tight).
 
Malcolm Leick said:
Thanks. Checked the handbook and you are absolutely right. Tweaked again but I still have a tight spot in one place.

I'll get the parts ordered.
Click to expand...

Have a word with Greg Masters of this forum. He is wise :rob in the supplying of things chain and sprockety, for reasonable prices to boot! :thumb
 
Rainbow had a quick look tonight and said the sprockets are starting to go. They have agreed to replace FOC as the original chain recall was never done. If the noise persists after that, I'm stumped. Setting off for a week long tour around Southern Ireland on Saturday so I hope the currrent set up holds out!
 
Nippy Normans supply Touratech, Wunderlich, Desert Fox and many other makes of accessories.
You must log in or register to reply here.


Back
Top Bottom