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pulsing gearbox

Discussion in 'Technical and Troubleshooting Torque' started by dah dah, May 17, 2005.

  1. Hi all,
    I have been riding my YZF600r Thundercat for a couple of months now and have noticed something that has got me curious.

    It could be the colder mornings, but I have been noticing that (after warming the bike until choke off) there is a pulsating feeling in the gear box. When I coast with the clutch in and engine at idle speed I can feel it most. After it is fully warm, it is hardly noticable. I have changed the oil and that has seemed to help a bit.

    Is this normal, am I paranoid?

  2. It's alive!

    I don't imagine it's the gearbox. More likely the plugs are fouling a little on choke, then cleaning themselves up after running wihout choke.
  3. I like that idea, I didnt think it was too serious
  4. Or maybe one of your brake discs is a bit warped? That might give you a similar sensation, and it can be easier to spot when you're coasting.

    Just trying to be lateral! :)
  5. Dont think it is a disk, as I cant feel it through the brake lever, and it goes away after it gets properly warm.

    Does a chain change much when it warms?

    Any thundercat owners experience the same?
  6. The reason I thought about a disk was because I've a similar problem with my car.

    When I had new brake pads put in, the dealer told me the front disks were a little grooved and asked if I had experienced any vibrations when braking.

    I told them I hadn't, and on that basis they said they wouldn't machine the disks as I wasn't experiencing any problems.

    I don't have any unusual sensation through the pedal when braking, but I've noticed a noise v.similar to the one you've described - easiest heard with a window open at low speed (eg coasting). (The brakes work fine.)

    Just a thought, anyway!
  7. That is so odd... My mate has the same problem every 15,000km on his Thundercat as well. The reason why it reoccurs is that he kills the chain... for some reason unknow to me he ends up with tight spots on his chain...

    Almost to the dot every 15K he brings the bike in for a new chain and sproket set. Every time I have put on a different brand name chain and new sprokets... So my theory is that I adjust the chain after the initial wearing in time coffectly... than he over tightens it onece or twice causing unusual ware...
  8. Tight spot in the chain! yes that was my prognosis, but I tightened it a bit and it didnt make much difference, and it goes away when warm? hmmm
  9. Be care full with tightening a chain with tight spots...

    Find the tight spot and measure the slck there... other wise it will be to tight and the chain will deterioate real quick...

    PM me if you want a new chain and sproket set...
  10. If it "goes away when warm" then most likely it will be fuel system related (electrical systems will tend to work best when cold)....

    However - can you decribe "pulsating"? Why did you initially think "gearbox"? Does the problem occur under power as well? Have you looked at the sparkplugs? - if so describe the deposits....

    There is a problem that can occur - that it gearbox related and it does feel like pulsating sometimes....but typically only a one or two gears and under power....You don't want that as it is typically a bent shifter fork (and a couple of stuffed gears) ......Chain? MMMmmm...maybe but I would say unlikely - do what the guy above says and see if it is within tolerances...

    Get back to us...

  11. You did mention that changing oil made a slight improvement. Could it be internal friction/resistance in the gear box as the oil would be cold and of course thicker. As the oil warms up, it becomes thinner and flows better meaning less film resistance. An engine can warm up, and a temp guage will confirm this. But that is more so heat from the combustion chamber. For other components of the engine and gear box, their heat is more so generated from riding which takes time to catch up. Perhaps try a syth oil as they often have a wider viscosity range. Just a thought.

  12. Hi guys,
    I thought it was the gear box as the left foot peg is where I can feel it the most. I still think it might have something to do with the chain or sprockets because the 'pulse' seems like it would be in line with a full rotation of the chain.

    It doesnt happen under throttle, in fact it is riding very well, can feel it most when coasting at low speed. 60km+ feel it a lot less.

    The other thing i tried is rolling down a hill in gear with the motor off and clutch in, but the engine was still a bit warm then - there was a bit of the feeling, and the chain was quite a bit noisey as well (normal?).

    and using fully synth oil

    Tonight I gave the chain another clean and lube and I will see how it goes in the morning.

  13. Hmmm...you are the best judge as to where it is coming from. Chains often have sections that are a little "stretched" more than others. Which of course means that as that section runs over a sprocket it can make a vibration and/or noise. Warm chains always have less resistance than cold ones as well. One way of checking is to check the slack in many diff locations to see if chain stretch is the issue. Or turn the rear wheel by hand and run your finger against the chain to feel for any significant irregularities. The other thing it may be is the front sprocket. Often I have seen these to be the culprits as well as they are often outta sight. This is also especially the case when sometimes chains are replaced and "new sprockets are fitted". Which does not always mean both sprockets are changed.

  14. I suppose if I cant figure it out, its off to the mechanics!
  15. Well, its fixed! - I went to one mechanic and he said that it needed a new chain and sprockets, so i waited until the netrider night to get them (good idea). I then went to another mechanic to fit them and 3/4 way through the job he discovered hard crud on and around the front sprockt, this was making the feeling! He also noted that the original chain and sprockets were not very worn - good thing I didnt go to the first mechanic or buy their gear.

    So im happy its fixed, but dissapointed in the original diagonsis. wont be going back there! - but back to being smoooth!