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Bad vibes

Discussion in 'Technical and Troubleshooting Torque' started by Iondah, Nov 8, 2006.

  1. I've been test riding a few bikes recently, one of them which I really liked the look was a 1997 Yamaha SRV250 which I basically had my heart set on until I took it for a spin.

    The problem was that when I got off, the thing I felt like I was sitting on a jack-hammer instead of a bike. The thing was vibrating so much that even at 60km/h in 4th I could barely read the speedo. I was very disapointed because its a beautiful bike to look at with a lot of character. Just the absolute pits to ride... since then I've got my eye on a Zeal which is SMOOTH as. Anyway...

    What makes a bike vibrate like that, and is there something seriously wrong with it or just how some bikes are?

  2. That could be your problem right there. The SRV may be a 'V' twin, but it still needs revs, and you are probably lugging the poor thing at 60 in fourth. My ex-wife had one of these, and they do vibrate a little like all 'v' twins, but no more than any other as I recall.
  3. It is a V-Twin.... 60 in 4th was just a guess though (didnt take note of exactly which gear I was in). I was trying to fang it a bit so low revs wasn't the problem. Even when sitting idling the thing was buzzing all over the place.
  4. There must be something wrong with it then, it's exactly the same engine as a 250 Virago, and they are not known for bad vibration. I suspect a timing or spark plug problem, or loose engine mounting bolts.
  5. I'm with Incitatus on this, shouldn't be that rough. I own one an its much smoother than a CB250 when revved.

    BUT.... Its not quite the same motor as a Virago, the bottom end is the same but the heads have been modified and they run more aggressive cam timing. So if you're off the cam it'll be rough but that should go away completely once you've wound it up.

    60kph in 4th seems slow. I'll only be in 4th at that speed when slowing down. That's 3rd gear territory. They have a rev limiter so you won't over rev it. 4th is good for 110kph with plenty of revs left. Are you sure you didn't go into 5th accidentally ?


  6. yeah, even my old parallel twin Yamaha XS-650 didn't vibrate as badly as you describe here
  7. I rode one years ago. It wasn't like you describe, Iondah.
    I strongly suspect the one you were on may have been running on one cylinder. See if you can find another one to try before making up your mind.
  8. they run more aggressive cam timing.

    never heard of agressive cam timing, please explain.
  9. its where the cams are enthusiastically punctual with a hint of anger :p
  10. lol, yeah, theya are more aggressive and have less patience.

    What I mean is that they generate their power higher up in the revs. The trade off is they are not as smooth at lower revs.

    Its the same as race car cam timing vs road cars. Normal road cars are tuned to generate their power at lower revs with more torque down low so the car is smoother and easier to drive, but this comes at the cost of a lower peak power.

    In the race setting, smooth power delivery at low revs isn't as important, but overall higher horsepower is so the cars are tuned for the higher power.
  11. so it runs different cam timing? so its not pissed off at you or anything?
  12. cams are the egg-shaped thingo's that open your valves to let fuel in and exhaust out.

    the higher the lumpy bit is, the more it forces a valve to open, therefore letting in more fuel. if the lumpy bit is lumpy for longer, it lets more fuel in for longer.

    i assume when you mention cam timing you are talking about the period of time for which the cam opens a valve. because other than that 'timing' is the relationship between inlet/compression/IGNITION/outlet and exhaust. to sum up (for a four stroke) its how the bang bit is timed to keep the motion of the engine perpetual.

    i too have never heard of "cam timing" before
  13. My ex had one... wonderful little bikes they are!

    They do vibrate a bit on the over run but they have to be the best looking modern 250 around :)
  14. That's it. Cam timing just like ignition timing relates to when things happen relative to the piston position.

    Some different cam timing parameters are;
    -Duration (for bot inlet and exhaust valve, how long they are open)
    -When the valves open and close
    -Overlap (how long both the inlet and exhaust valves are open together)
    - Lift (how much the valve lifts)

    Changing a cam on any given engine to a different one with different settings (like those above) will change how smoothly the engine runs at low revs, how hard it revs, etc. Just like changing the ignition timing can change how an engine behaves or misbehaves. :)

  15. Must be sumfing wrong with it - I bought one new in 1996 and had no vibration over and above 'normal' whatsoever. Revisit another one as mentioned, they're a top little bike.
  16. Well, I didn't buy it but it sold that weekend so I guess someone liked it!