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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: Mongrel on August 19, 2018, 02:23:46 PM
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So, at around the 60 kmh mark, or right below around where I usually shift from 3rd to 4th, I've noticed a pulsing deep within the drive train, possibly from the clutch or tranny. It's most pronounced when you're in the low ranges of 4th gear, so I've adapted by waiting slightly longer to shift from 3rd to 4th, but I can still feel it faintly and much faster in the high end of 3rd gear.
This smells like it might be a transmission issue to me (luckily I already have a replacement handy), but I'm interested in hearing other thoughts before I try to dig in and figure out what's going on.
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I think you're lugging the engine if you shift from 3rd to 4th at 60 KPH. I cruise all day at 60 KPH in 3rd and don't shift until about 80 KPH.
How are you sensing the pulsing? Vibration through the handlebars? Sounds? Variation in road speed with a constant engine speed?
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My bike has the typical change in vibration/engine feel at about 4.5k revs or so that seems typical of K bikes, is it that you are feeling?
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hard to diagnose like this, but my first thought was the u-joint. No good reason that would just manifest itself in 4th, does it do it when coasting in neutral? Then try coasting in 4th with the clutch in. That might narrow it down.
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I don't recall any pulsing in neutral coasting in 4th, though I'll double check when I go out today. Hard to describe exactly how I feel it, but basically through my feet and butt - it doesn't seem like it's coming from further back.
@Rob: Historically, mine doesn't lug if I shift around 65 or so (which is the actual speed I usually shift around). I think I'm usually dropping from ROUGHLY 3500-3700 to 2500-2700 RPMs on that shift? The pulsing is definitely new in the past few months. About since we changed the tires, so I wonder if something happened then. It's not the balance, because Ed did a very careful and thorough job in balancing the wheels.
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Small update. Wasn't easy to even get out of 3rd in the first place given the usual Toronto traffic, but I found a few stretches here or there :riding:
No pulsing when coasting with the clutch in while in 4th, and I actually do feel the pulsing somewhat through the handlebars. Definitely seems to synch with engine speed more than ground speed.
Also my guesses for RPMs was way off, lol. I do usually shift from 3rd to 4th around 65kmh on level ground, but this is almost always from 4000 RPM in 3rd to 3500 RPM in 4th (and I'm almost instantly back to 4000 and rising if I'm still accelerating). Not that I think that affects troubleshooting much.
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My bike has the typical change in vibration/engine feel at about 4.5k revs or so that seems typical of K bikes, is it that you are feeling?
By the way, this isn't it. I know what you're talking about - that higher pitch of the engine getting into its high RPM sweet spot. That's definitely not the issue here.
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It could be:
- Incipient bearing failure in the rear drive. Raise the wheel off the pavement, grab it on both sides and see if you can wobble it or shift it fore and aft.
- It could be a failing driveshaft.
- It could be an effect from loose mechanical connections—tire bolts, rear drive bolts, transmission bolts, etc..
- It could be an effect from the loss of a wheel weight.
- It could be you have hypersensitive buttocks and appendages so vibration damping cushions, an electric moto or an avocation in relevant product testing might be considered. :2thumbup:
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I don't think it's the first two. I recently installed a new driveshaft I bought off Rob and they were in really nice shape and the rear drive is a replacement as well. I'll check the rear drive anyway, and go over the other stuff.
Except for my ass - my wife's more qualified to perform that inspection. :hehehe
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Well, checked everything but the driveshaft. Guess it'll be time to lube up soon enough anyway, so I'm sure I'll see that then.