Pulsing/vibration.

Discussion in 'Parallel Universe' started by fiwi, Aug 27, 2012.

  1. fiwi

    fiwi Been here awhile

    Joined:
    May 10, 2009
    Oddometer:
    148
    Location:
    Perth, Australia
    Hello all. I have an issue i woiuld like your opinion on. I posted it here a few months back but seeing as I havent riding the bike alot lately I let it slip. Time for me to get it sorted out.

    Roughly around the 15000km mark, my bike started displaying what can only be described as a pulsing/vibration, peaking at around 3200rpm, and only in 5th gear. Every other gear is fine. I took it into the local BMW dealer and they gave me the usual line, feels normal. Whatever. I was notified of a chain recall when the bike was at 18000kms. Got the chain done and to my surprise the pulsing/vibration was no more, great.

    Recently I took the bike away on a long trip. Everything was going fine till the bike hit around 30000kms, when the pulsing vibration came back. Once again peaking at around 3200rpm, and only in 5th gear. All up i guess I notice it to some degree for a range of about 500rpm. It is very noticable, to the point where I dont like using 5th gear in that range at all. I feel it in the hand grips and through my feet. It is very constant, very rhythmic. I tested it on the way home from work last night. It pulses at a rate of about 160 pulses/vibrations per minute @3200rpm, which is about 73kph, or close to it. If I clutch in and coast at that speed the vibe is gone, so it is when the bike is under load only, so I assume that it isnt the chain or sprockets. I have tested the chain for stretch, checked it right the way around the length of the chain and it appears to be fine. I could be wrong.

    I dont have a huge amount of mechanical knowledge, but I have a couple of queries about this. I originally thought it may be chain or sprockets, due to when it happened the first time, and i had the chain recall done, it seemed to fix the problem. What i cant figure is that if it was a problem with a certain point on the chain, or a sprocket, then at 72 kmh the pulses would be alot faster that 160 per minute, given the length of a chain or the circumference of a sprocket, you get me?. I dont understand what would cause a constant 160 vibes per minute at that speed. I dont understand how the internal gearing works but once again, Im sure nothing has a cycle rate? that slow.

    I dont just want to go out and buy a chain, sprockets and chain tool straight away, a few hundred dollars worth. It could be wasted money. Any thoughts?.
    #1
  2. MikeMike

    MikeMike Long timer

    Joined:
    Feb 28, 2009
    Oddometer:
    4,150
    Check that you haven't lost a balance weight from a wheel.

    Have you done a thorough cleaning of the chain? I mean really degrease it, scrub it, and check it link by link?
    You might find "fronzen" links or a specific tight spot, a location on the chain that is way tighter than other points.
    Check your sprocket teeth for "hooking" where the sprocket teeth take on a distinct "wave crest" type look where the point is ahead of the base. Front and rear sprockets will be, of course, hooked in different directions due to loading.

    Check that your motor mounts are torqued correctly, however I doubt it is that.

    The last thing, when you do your oil change, check for metal debris, more than the usual fine amount, on the magnet in the drain plug. The internal bearing on the clutch side could be going south. But you'll likely hear that easy enough.

    Just a few ideas for you.
    #2
  3. Snowy

    Snowy Long timer

    Joined:
    Dec 2, 2008
    Oddometer:
    2,390
    Harmonic.

    Tyres, chain, sprocket sizes/wear, gearbox output bearing (check chain tension - make suer it's not over tensioned) and the vibrations from the parallel twin are all coming together to produce a harmonic.

    Ride with a half helmet (skull cap, pudding bowl - what ever you guys call them over there) and it'll sound like the chain is slapping against the swingarm as the surging starts.

    It's a motor that's prone to harsh vibration at very specific points in the rev range, which is why it has a dirty big counter weight in the sump. Combine that with secondary vibration of any kind and you get a harmonic when the vibration frequencies line up. So it appears as a much lower frequency "pulsing".

    If you have ever worked on an in line 4 with a counter balance shaft, and assembled it one tooth out of sync, you'll know what I mean.

    I did a lot of Mitsubishi engines 20 years ago and they often didn't have clear marks on the timing drive gears. So you'd end up one tooth off with the counter balance shaft. Hard to know for sure as they still felt remarkably smooth when revving them. But they'd have one point in the rev range where the out of balance caused a harmonic.

    My method for testing was to put a glass of water on top of the engine and gradually bring the revs up to redline. You hit the point where the harmonic occurs and the water just disappears. The glass a split second later. That's how bad a harmonic can be. A very narrow rev range of maybe 50 rpm where the engine just tries to shake itself to bits.

    A combination of factors is causing a similar issue in the BMW drive train. Mine has it, as did the other 2 I've ridden. I figure it must be normal. It hasn't broken....that bit....yet.
    #3
  4. MikeMike

    MikeMike Long timer

    Joined:
    Feb 28, 2009
    Oddometer:
    4,150
    Two things I have noticed in the 3 years with my F650GS is that 5th gear at 100kmh is the very smoothest and it is overall, way smoother between 140kmh and 160kmh on the highway than between 110kmh and 140kmh.
    Oddball bike.
    #4
  5. Lokey

    Lokey redneck

    Joined:
    Sep 28, 2009
    Oddometer:
    252
    Location:
    Susanville, CA
    My F8 does exactly the same thing (fifth gear pulsing) with about 14K miles on it. I feel it is a product of riding for two weeks in the rain in Canada and Alaska and not being able to lube the chain properly. My can of chain lube emptied itself and it took me a few days to find another can. Shortly after that I noticed the pulsing and it has done it since then.

    If you look at my chain it has links that look slightly kinked even though it has been lubed. I feel it is a product of the harmonic vibrations that Snowy mentioned and sympathetic vibrations that develop at a particular RPM + tire speed + chain wear. I adjusted the chain and have largely eliminated the pulse, but it is still there.

    I am going to take a five day trip this weekend to Northern California and am planning on replacing the chain and rear tire when I get home. While the chain shows no real sign of being worn out outside of the kinks, I feel that and a new tire ( old one is a Heidenau K60 that was installed in Fairbanks) should fix the problem.
    #5
  6. fiwi

    fiwi Been here awhile

    Joined:
    May 10, 2009
    Oddometer:
    148
    Location:
    Perth, Australia
    Ok, I hear where you are coming from. One thing I don't understand though. As I said, the vibe/ pulse is at the rate of about 160 pulses per minute at 72 kmh. I would have assumed that any pulse/ vibe in relation to the chain would happen on every rotation. 160 pulses per minute is way too slow for that. In saying that, I don't really understand this harmonics thing very well.
    #6
  7. MikeMike

    MikeMike Long timer

    Joined:
    Feb 28, 2009
    Oddometer:
    4,150
    Lokey, did your vibes start when you fitted the K60?
    #7
  8. JRWooden

    JRWooden Long timer

    Joined:
    Jul 5, 2008
    Oddometer:
    4,646
    Location:
    The great state of confusion
    Fiwi:

    It would be an interesting (and fairly easy to perform) test to swap out your front sprocket for a sprocket with one more or one less tooth just to see what happens. Stock on the F650GS-twin is 17T.I know they make an 18T and the F800GS comes with 16T maybe a pal has one you could borrow?

    If any pals have a chain with a master-link in it perhaps you could do a chain swap for grins as well?
    #8
  9. CheckerdD

    CheckerdD Long timer

    Joined:
    Apr 30, 2005
    Oddometer:
    1,433
    Location:
    Dave Rankine, Reno NV
    My guess is your front tire may have gone a bit out of round. Spin both the wheels with the bike on the center stand. If there is a bit of a wobble you may have found your culprit. If the tire is starting to cup a bit that can cause the same problem. As someone else pointed out you can get similar symptoms if you threw a wheel weight. Dave
    #9
  10. JRWooden

    JRWooden Long timer

    Joined:
    Jul 5, 2008
    Oddometer:
    4,646
    Location:
    The great state of confusion
    If it was a tire problem wouldn't it be just related to speed and not which gear the bike is in?
    e.g. 60mph in 5th gear or 60mph in 6th gear would have same vibration?
    #10
  11. fiwi

    fiwi Been here awhile

    Joined:
    May 10, 2009
    Oddometer:
    148
    Location:
    Perth, Australia
    That's right JR. A stuffed tire or rim wouldn't just affect 5 th gear at 3200rpm. Also when I pull the clutch in and coast the pulse/ vibe is gone. I don't understand how the gears work as such, but is there anyway 5th gear could be stuffed?. Do gears/ cogs become problematic?. Sorry, my knowledge and terminology on this topic is lacking.
    #11
  12. fiwi

    fiwi Been here awhile

    Joined:
    May 10, 2009
    Oddometer:
    148
    Location:
    Perth, Australia
    JR, can you please tell me the reason for trying a front sprocket with more teeth?. I'm willing to try anything. I don't know anyone I can borrow a sprocket from but for $50 I'm quite happy to buy one. Not so keen on doing the experiment with chain yet as it becomes expensive if the. Bain isn't the problem.
    #12
  13. itsatdm

    itsatdm Long timer

    Joined:
    Jun 19, 2004
    Oddometer:
    5,371
    Location:
    Nor Ca.

    I guess 5th gear could be stuffed, except it is not one of those things being reported at a problem. What you are describing can occur if you have a frozen link, which is not uncommon. My experience is, buy a new chain.

    Pulling in the clutch is not a test for a frozen link, there is no torque being applied to it. Look at your chain again.
    #13
  14. fiwi

    fiwi Been here awhile

    Joined:
    May 10, 2009
    Oddometer:
    148
    Location:
    Perth, Australia
    I am trying to steer away from new chain and sprockets for now if I can, but possibly that is the only way to eliminate them as the culprit. Call me slow, but I still don't get it. If there was a kink in the chain then surely at 72kmh the pulse rate would be a lot faster than the 160 per minute I counted. And 5th gear only. Tomorrow I will do a
    Bit more testing on the chain. Thanks all.
    #14
  15. JRWooden

    JRWooden Long timer

    Joined:
    Jul 5, 2008
    Oddometer:
    4,646
    Location:
    The great state of confusion
    The "only in 5th gear" thing really has me :huh:huh:huh:huh:huh:huh:huh:huh:huh

    Just to confirm - you are saying that if you:

    1) drop to 4th gear while maintaining constant SPEED it goes away (because the RPM goes up?)
    2) shift up to 6th gear while maintaining constant SPEED it goes away (because the RPM goes down?)
    3) hold 3200 RPM in either 4th or 6th gear there is no problem?

    It makes me want to ... :1drink

    I suggested a different chain and countershaft sprocket because it would be interesting (and if you didn't have to buy the parts ... not too expensive) to see if the problem went away with a new/different chain, or it the problem moved to a different RPM range if you changed the front sprocket.
    #15
  16. PatrickM

    PatrickM Been here awhile

    Joined:
    May 6, 2012
    Oddometer:
    415
    Location:
    Zephyr Cove, NV
    If it were a car I'd suggest looking at the motor mounts.
    #16
  17. fiwi

    fiwi Been here awhile

    Joined:
    May 10, 2009
    Oddometer:
    148
    Location:
    Perth, Australia
    Yes JR, that is exactly what Im saying. I cannot replicate the pulse in any other gear at any other speed, no matter what I do. Weird.I did another inspection of the chain and sprockets and they seem to be fine. I am booking the bike in to get the brake fluid changed over the next couple of weeks. I will get them to have a look at it. Call me a pessimist but I can guess what their answer will be.
    #17
  18. MikeMike

    MikeMike Long timer

    Joined:
    Feb 28, 2009
    Oddometer:
    4,150
    If it's 5th gear or transmission related, your drain plug will be sporting a very distinct afro of metal.
    It'll take you about an hour to:
    Change the oil and filter and get a good look at your drain plug's magnet
    Check the wheels for lost weights and out of round
    Clean the chain link by link and see if you are missing o-rings or have frozen and kinked links
    Check the sprockets
    Check your chain tension
    Re-torque the motor mounts
    Check tire pressure
    And test ride
    #18
  19. Cambi

    Cambi Adventurer

    Joined:
    May 31, 2010
    Oddometer:
    73
    Location:
    Budapest expat
    Hi fiwi - add me to the list - 2010 - 24 000km - started about 1K or so.
    It's prety light on 5th gear around 3000RPM but just like you - I now avoid hanging there - vibration seems to come from the left hand side of the engine.
    This is how I feel it.
    #19
  20. JRWooden

    JRWooden Long timer

    Joined:
    Jul 5, 2008
    Oddometer:
    4,646
    Location:
    The great state of confusion
    I think MikeMike's list is a good one ... I still am going at your symptoms....:huh
    When you get to the shop maybe you and one of the techs could go for a ride with two bikes - yours and something for comparison ... a few miles out switch bikes and come back in to the dealership....

    weird issue ...
    #20