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weird intermittent hesitation on the TT250
I've been reluctant to ask about this for awhile now because it's so intermittent. In that, I mean at 8k miles it's probably happened maybe 10 times, and hopefully I can accurately explain it.
The best way I can relate is that it feels as if when you are on a bicycle, and the chain slips off for just a brief second. It's only happened in 5th, and only over 45mph, but most often will happen at full throttle when I'm trying to keep up on a 55mph road. Just a real quick "zip" for about half a second where the power is lost and the engine revs, and then immediately back to normal. I have yet to see something abnormal in my chain or sprockets. I suppose the same thing might happen if I pulled in the clutch for a second, so my best guess is it has something to do with that. Could this be clutch fade, like I've heard mentioned on these engines? What does that even feel like (or mean, for that matter)? |
Are your hands on the clutch lever when it happens? I've had the same hesitation on my Hawk. It turned out that when I hit a bump I was accidently hitting the clutch lever so the clutch briefly slipped.
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I don't believe so, but I'll pay attention next time, maybe I'm just not noticing. I keep 2 fingers on the brake 100% of the time but never on the clutch when cruising at a steady speed, as far as I can recall...
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Nah, not likely clutch fade. When you end up with clutch fade the opposite tends to happen. The clutch starts to drag when the lever is pulled back and it can make shifting to neutral difficult, or getting into gear from neutral a bit harsh.
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Is your clutch lever adjusted properly? Are you using a wet clutch compatible oil? And is yer hoof riding on that shift lever? I'm just thinking out loud.
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I understand the presumption that the clutch is involved since it is like the clutch is slipping transiently. But I wonder if the guide yoke(s) on 5th gear(s) is not fully engaging the dogs.
Does shifting into 5th feel like a deliberate "full throw"? If the rotating shifter guide that positions the yokes is not completely in the fifth gear position, the dogs could be incompletely engaged. I am calling those guide yolks because I don't know the proper name for them. They moved transversely on certain gears on the counter rotating shaft, and drive shaft when you select a gear. Maybe get the rear wheel off the ground and manually go through the gears (shift with left hand while rocking the rear wheel back and forth with right hand so the dogs can align). See if it feels like a solid and complete chunk when it gets to each gear position, particularly between 4th and 5th. Do this with engine not running, of course. |
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I think so, but it did happen awhile ago and I have since adjusted the clutch, and it's happened since. Maybe I'll recheck that again just to be sure. The ol' hoof isn't riding on the lever, I'm pretty good about getting right back to ball-of-toe being back on the foot peg immediately after a shift. |
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Interesting, I have no idea what any of that means :tup:. But I'll give it a try to see what happens. It does feel like the shift into 5th is a "full throw", just as solid as all the rest. Like I said, this happens maybe one time, sometimes a second time a few seconds afterwards, and that's only about every few months of riding, and I ride a few times per week at the least. It's not a major pending concern at that rate, but I'm just trying to get a grasp on what might be happening in case it starts to get worse. |
Here's a good article on how it works (with correct termnology!)
https://www.uti.edu/blog/motorcycle/transmission The things I called guide yokes are called shifting forks. This animation really nails it, and makes it easy to understand. The shift drum needs to get fully to the next position to get the gears lined up so the dogs are fully planted. The video shows the detent with a sprung roller that holds the drum in position when in a gear. They call the counter spinning axel the input shaft, and the drive shaft (with front sprocket) the output shaft. https://www.youtube.com/watch?v=g8xnIFf4id4 |
I had a small pickup with a 5 speed. When the synchronizer in 5th gear went out it wouldn't stay engaged at all. I had to put a strap over the shifter to hold it in gear or it would throw it out. The transmissions are made on the same principle with 2 shafts and shifting forks. If it kicked out there would have to be something to push it back in. You may have to tear it apart to find out. Seems more like the clutch being pulled and then released or the clutch pads overheated and slipping. I would look at the clutch pads.
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