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Why Can't I Red-line?

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by Levih, Jun 29, 2009.

  1. Hi there,



    I was just wondering how come my CBR125R starts to valve bounce at 8000rpm, whne the Red-line is, dam cant think off the top of my head but like 11-12k?

    Cheers,

    Levi
     
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  2. Try to find out if it has the correct ignition module. It may be a case of the rev limiter cutting in.
     
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  3. yep rev limiters make it bounce

    do 125's even rev that high??

    what get you trying it in? maybe its a saftey thing to stop you from burning out a lower gear
     
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  4. This is in every gear, when i get to 6th i have to slow down sometimes cuz im revs are getting close to bouncing
     
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  5. When you say valve bounce, I hope you mean bouncing off the limiter? :shock:

    I'm trying to find a dyno chart for the beast, but with a single, there may not be much point revving any harder.

    Anyone know where peak power is?
     
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  6. Does it have an adjustable rev lmiiter programmed to the ecu?

    There are bikes that you can set your own rev limiter - not a bad idea if you want to run the bike in by the book.
     
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  7. Does it rev past that in neutral? You've got a new batch of things to look at if it just wont rev with load on it.
     
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  8. Lol guys im really new to bikes and have no clue what you guys are talking about, englighten me?
     
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  9. Having a rev limiter is the bikes "Computer" stopping the bike reving up harder, it will just die in the ar$e when it gets up near redline or at redline, its the manufacturers stopping you from destroying your bike.

    Valve bounce is when the valves have a like a resonance effect at a high enough rpm for it to kick in that is, and don't stay seated, basically it means its not in the position it should be at that point in time.

    Im sure you can find more on this interwebbie thing to satisfy your curiosity.



    I think your problem is you have a tiny tiny tiny tiny bike and your looking for power it just dosent and will never have.
     
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  10. FWIW, the official specs say peak torque is 8,000rpm, peak power is at 10,000rpm and redline is 11,000.
     
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  11. Red line is the danger zone on the tacko,go there at your peril,valve bounce or float is when you rev the motor to the point where the valve springs are overwhelmed and valve control is lost,its suppose to come off its seat with contact by the cam and return to its seat by spring pressure,when the spring cannot react in time to seat the valve you have uncontrolled and untimed events happening,which can result in valves kissing pistons= expensive bills.
     
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  12. SO peak power is what i should be able to get up to then?
     
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  13. Yes, the engine should be able to rev past 10,000rpm.

    Most modern engines will perform a brief ignition cut on or just before the redline in order to prevent the engine overrevving; in this case the CBR125R should be cutting out somewhere between 10,500 and 11,000 most likely.

    But you should definitely be able to reach 10,000rpm.
     
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  14. The redline issue has me interested in what it really means. Someone (an ex-mechanic but it doesn't really matter about his occupation) once told me that revving past redline doesn't matter if you've got it under load but if you're keeping it constant there (no/hardly any load) then it will damage the motor. Is that pretty much a simple but accurate statement?
     
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  15. Basically when they design the bike they have to set a safe limit to what can rev to.

    As I mentioned before some have an adjustable 'redline' which is more of a power cut to the engine.
    Sometimes people will use it to control the torque on the bike in certain conditions.
    When I went for a recent ride one of the guys with a new aprilla 1000 set his redline a little lower for the break in period and increased it a couple of times.
     
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  16. Ok, so mine is limited at 8k rpm,

    Now how would i adjust this through the computer?
     
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  17. What is a redline? As Geeth said, it's the end of the "safe operating zone" for the engine as designed by the engineers, beyond which you're placing excessive stresses on the machinery and may/will cause engine damage.

    Though it's not an absolute be-all-end-all...

    For example, the 1996 Toyota Camry manual says the engine shouldn't be run at >4500rpm or so for prolonged times even though the indicated redline and ignition cut is more like 6000. The oil pump can't keep up at engine speeds >5000rpm and so you risk oil starvation followed by catastrophic engine failure. ;) But there's little point running it up to the redline anyway because the engine becomes severely asthmatic after 5000rpm.

    On the other extreme, my Tiger 1050 will actually allow very brief forays beyond the 10,000rpm redline in 1st and 2nd gear, in case you don't quite change gears before the engine hits the redline. A friend's VFR750F behaves similarly, allowing brief overrevs. It's really only a courtesy rather than an invitation, however.

    Beyond redline is most certainly not a good place to be for any great amount of time.
    * The faster the engine revs, the greater the stresses on the conrods, crank and throwout bearings, resulting in a shorter engine life and ultimately engine failure.
    * Coolant pumps and oil pumps may not be designed to spin that fast, resulting in lack of cooling/lubrication and then engine failure.
    * As engine speed increases the valve springs may be overwhelmed, resulting in valve bounce/valve float, and on an "interference" engine this will most certainly result in engine failure.

    In short, the redline marker is where the engineers have written "HERE BE DRAGONS" and "ABANDON ALL HOPE YE WHO ENTER HERE".

    But then, there's very little point to overrevving an engine anyway unless you're on a particularly technical racetrack or autocross course.
     
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  18. maybe becuase its a new bike? and they are factory limited till they are fully run in properley? consult your manual /dealer
     
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  19. Thanks for the answers. I was interested on what the condition generally is which results in trouble when operating in the red zone (like the example I gave). I was a bit surprised to read that there are engines out there which have oil pumps that just can't keep up when the engine spins past 5,000 rpm (which effectively makes that the weakest link).


    Levih, maybe try doing a search for other CBR125R owners and ask them if they had the same issue when they had it from new and whether they had the restriction lifted before the run-in period.
     
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  20. Yeah good idea GoTeam, cheers.
     
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