Vibration at 4k rpm and up

Discussion in 'Mechanics Garage' started by Miketegra, Sep 16, 2006.

  1. Miketegra

    Miketegra New Member

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    Well, as the title says, I'm experiencing some pretty noticeable vibration at engine speeds over 4000 rpm's. It doesn't seem like it's the chain or suspension because the vibrations disappear when coasting at speed (pull the clutch in and let the revs drop). The vibration is also present when the bike is in neutral or in gear with clutch in, just revving it over 4k sitting in the driveway.
    It seems to idle smoothly and throttle response seems normal.
    Relevant Data:
    1995 VFR 750
    15,500 miles
    Yoshimura carbon slip-on
    Unknown jetting situation, but seems ok...no backfiring or rich smelling exhaust
    Most likely original R/R, but I have not checked
    Due for 16k service soon, so plugs are probably pretty old, valve lash has not been checked lately either.

    So far, the only things I can think of are:
    -bad carb synch
    -loose engine mount
    -fouled plugs
    -small gremlin in #4 cylinder ;)

    So any grease monkey's out there have thoughts on the matter?

    Mike
     
    Last edited: Sep 16, 2006
  2. WhiteKnight

    WhiteKnight Well-Known Member

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    It could be those, but does the vibration go way at any point above 4000 rpm? There is some natural vibration (due to harmonics) between 5000 and 6000 rpm, at leat on my 93 model.
     
  3. RVFR

    RVFR Member

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    hmm I'd be taking it in for the 16k service a bit sooner. Also if it were me I'd be all over every nut and bolt, but because it's so 4K rpm and up specific I'm thinking it's inside, but to tell for sure I'd have to see, hear and feel it myself to be able to give you what I thougt it could be. I was going to say counter shaft sprocket lose chain. put if it goes away when doing like 40 and you pull in the clutch it goes away then it aien't that, but what gets me here is, you say it does it when in the driveway in neutral and you take it to 4K and up does it get worse say as you go up in rpms? what about neutral clutch out does it make a diff? when you pull the clutch in neutral of course you say it does but does it change in anyway as to get one to think it could be clutch related. man a good one, I'd like to know too, as I have a 97 thou it has 30K and runs like a very fast swiss watch..still good to know what you find, still think since it is close for the 16k service might as well bite the bullet and take her in. good luck, sorry not much help this time.
     
  4. Miketegra

    Miketegra New Member

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    I just did a little testing in the garage:
    It acts the same in neutral as it does in 1st gear with the clutch pulled in: Vibration starts at around 4k and seems to "follow" the rpm's....ie. the frequency of the vibration seems to keep time with the engine. The amplitude/severity of the vibration does not seem to increase with rpm's.
    Also, I noticed that when holding it around 7-8k rpm, I noticed a definite, but slight "surging" of the engine up and down....not too noticeable, but definitely there.
    Anyway, I plan to check the torque on the engine mounts, replace the plugs and do a valve adjustment in the next week or so. I'm trying to get in touch with an old friend who is a total Honda Guru Mechanic....he has a carb synch tool I hope to borrow, and he may have some good advice re: the problem as well.

    Mike
     
  5. RVFR

    RVFR Member

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    Good luck, lets us know how it turns out.
     
  6. Miketegra

    Miketegra New Member

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    I got in touch with my old riding buddy and Honda mechanic Gary.
    Went to his shop and let him rev the bike up a few times in the driveway. He seemed to feel there was no undue or excess vibration, and figured I was just used to riding inline4's and was not used to the V4's unique vibration. I pointed out that my windshield even vibrates noticeably at 4-6k rpm's, and my throttle hand goes numb, but again, he didn't think the vibration was excessive or out of the ordinary. I should have had him jump on and take it for a ride, but we were pressed for time.
    Anyway, we synched the carbs up, although they were not very far out of synch anyway, and changed the spark plugs. The old plugs looked pretty normal. Didn't have time to check the valves, but Gary figured 1. they were probably close to specs and 2. it wouldn't really make the bike vibrate anyway.
    So it seems that doing the carbs and plugs may have made an improvement, but nothing tremendous. Although, my hand didn't go numb on the way home, which I was quite happy about. I'm not sure if this was due to an improvement in the bike, or due to the fact that I hauled ass home and was running closer to 6k+ rpm's and not the usual 4500 or so...ie. my hand would go to sleep riding at more normal speeds that kept the tach down near 4 or 5k. This seems to confirm my recollection that the vibration actually decreases somewhat past 6 or 7k. If I recall correctly, the amplitude of the vibration seems to drop off at higher rpm's, but the frequency seems to increase along WITH the rpm's. (sorry if I'm rambling here....kinda thinking out loud :)) It rained today and will probably rain tomorrow too, but I will try to get out and give it a more thorough test-ride as soon as I can.
    I asked my buddy what he thought about loosening and then re-torquing the engine mounts and he thought that was a good idea. Unfortunately, to do it properly, I will need to get Honda tool 07HMA-MR70200 at $65, but seems like its worth it. Don't know if you have seen this post, but it looks promising: https://www-auth.cs.wisc.edu/lists/vfr/2003-April/msg01823.shtml
    I might take it to the dealership and let them look at it, but honestly, if my friend Gary thinks it's ok, I'm inclined to agree with him. Perhaps after he's ridden it, he can make a better assessment. Unfortunately, he is often out of town quite often on business and is running an XR650 in the Baja 1000 this year so he's got alot on his plate at the moment.

    Mike
     
  7. squirrelman

    squirrelman Member

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    Dija??

    did u consider that a worn out chain can cause vibrations like ur describing??
     
  8. reg71

    reg71 Poser Staff Member

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    another cheap thing that helps is gel grips. a lot of us on here run pro grips which are around $10 at most dealers...
     
  9. Miketegra

    Miketegra New Member

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    Yeah, I'm going to pick up a pair of better grips within the next few days.
    Here is a question though: do your (or anyone's) mirrors vibrate at certain rpm's?
     
  10. reg71

    reg71 Poser Staff Member

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    Mine vibrate a bit at 4k but I usually only glance at them quickly so I don't know if you'd call it 'bad' or not. At highway speed, I'm at 5-5500 rpm and they are some of the clearest mirrors I've had on a bike.
     
  11. RVFR

    RVFR Member

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    Nope, no vibs..
     
  12. avfr

    avfr New Member

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    Any news regarding the vibrations?
    My FS also have a the same described vibration but it appears from ca 3000 rpm`s.
     
  13. Miketegra

    Miketegra New Member

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    I really don't have any updates on this issue. I've just kinda learned to live with it and accept the vibration as part of the bike's personality.
    A guy stopped by the shop the other day with another 95 VFR and while I didnt ride it, I did feel the bike as it idled and was revved up....pretty much seemed like mine....it had a pretty similar vibration.
    I think my issue is that I was so used to the smoothness of inline four motors, that the v-four seems buzzy to me. I've pretty much accepted it as normal at this point. I've also ridden a few other bikes recently (RC51, Yamaha R1), and honestly, the vibrations on my VFR don't seem too out of line compared to the other bikes.
    Next time I ride into work, I'm going to have one of the mechanics take my bike for a ride and see what they think about the vibrations. Also, there is talk of loosening and then re-torquing the engine mounts as a possible solution.
    I'll keep you updated if I come across any solutions or information.
     
  14. Rev

    Rev New Member

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    Hmm, you may be on the right track with the engine mounts but I'd say you might have a bad isolation mount. I can't tell by looking at the fiche; do the mount bolts have rubber bushings? If so, maybe one is cracked, hardened or otherwise damaged.

    The other thing about riding around at 4000RPM is that is at the lower end of the range for the VFR. Try dropping down a gear which should put it in the 5000-5500rpm range (maybe not that high but you get the idea).

    Other questions:
    Did the bike sit for a long time unused?
    Does the vibration stay consistant or increase/decrease as the rpms go up?
    What color were the plug tips? Tan or black?

    If I think of the VFR engine as 1/2-a-V8, then I wonder if the engine has the equivilant of a harmonic balancer. And if so, does it/could it wear out?

    Having only 15K miles, that engine is pretty fresh. My '94 has been trouble-free for the nine years and 11k miles I've owned it; it even sat for a year in storage (with no prep) and it runs great. Dunno what else to say, will think about it. Hope my ramblings help.
     
  15. avfr

    avfr New Member

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    I dont think the VFR is supposed to vibrate so much. I am going to deliver mine to a garage soon. I first noticed the vibration when i was downshifting. A light trembling that i felt came from the rear of the bike. Checked chain and sprockets. Front sprocket was totally warped. All teeths worn. Changed both sprockets and chain. But still a vibration. I belive the excessive wear on a sprocket only driven 13 000 km is due to the vibration
    Did all kind of test like you described and found the same things as you.
    Checked bearings etc. but all seems fine.
    A friend of mine checked the bike and simply by measuring the temperature on exhaust outlets we found that the front cylinder to the right was running very cold. (100 degrees celcius while the 3 others had a idle temp around 170 degrees)
    i belive the fault lies in the carburettors. My friend adjusted some settings on the carburettor but it was still not correct. Better, but still some bad vibes.Sorry if my english is not up to date.
     
  16. Miketegra

    Miketegra New Member

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    avfr~

    Does the bike vibrate when revving, but sitting still in neutral? How about when you are riding at speed....pull in the clutch lever....does the vibration go away? Have you checked the engine mounts?
     
  17. avfr

    avfr New Member

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    Yes the bike vibrates when standing still and when riding at speed with clucth pulled in. But only when revving engine. As soon as it hits ca 3000 rpms it vibrate and it comes and goes up to about 7000 rpms. As soon as the rpms drops its a smooth ride. Have checked all engine mounts execpt the lower one that needs the special tool. All where thight.
     
  18. Miketegra

    Miketegra New Member

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    Not sure what to tell you except, maybe take it to a mechanic. You might also want to read the link in my previous post about the engine mounts. You are not checking to see if they are tight, but rather, loosening them all, then tightening them in the proper order and to the proper torque spec.
     
  19. avfr

    avfr New Member

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    Ok. I will make a post when a mechanic has gone over my bike. Maybe he finds something of interest to all with the same problem.
     
  20. avfr

    avfr New Member

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    Hi
    A little update. The bike has been to a "doctor" and he found that there was something wrong with the spark plug caps on two cylinders. Enough contact to make the engine run but bad connection made the engine misfire at certain rpm`s
    He measured the voltage/amps ? running thru the wires and noticed that something was wrong.
    He just removed the old ends, shortening the wires and reconnected the spark plug caps and all was fine.
    Just talked to him on the phone and hope this solves my vibration trouble.
    Will update when i have driven the bike myself.
     
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