Bandit Alley
MODEL SPECIFIC => SUZUKI BANDIT 250 & 400 => Topic started by: Squishy on November 14, 2015, 01:21:36 PM
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Hello,
Since my 4000km trip last summer (where my 400 got hammered :motorsmile:) I've noticed a shake in the rear, felt through the footpegs. I feel it about 4 times a second at 50km/h.
I figured it was something like the chain, rear wheel bearings or output gearbox shaft bearing..
After I checked all of these but found nothing (chain is only 1.5 years old and well maintained, no play on rear wheel/output shaft), I did some test rides to locate the problem better, and noticed it was only happening in 3rd gear. It's worst at around 4500rpm, 50km/h.
In 2nd gear or 4th gear at 4500rpm or 50km/h there is nothing.
Does anyone have any experience with this kind of symptom? Is a symptom of a worn gear sprocket?
There's no play on the output axle, and even put in 3rd gear at 4500rpm on the center stand, but axle looked perfectly stable.
Thanks
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Is it only on constant throttle? Or is it acceleration/ deceleration?
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Is it only on constant throttle? Or is it acceleration/ deceleration?
It happens on constant throttle, and also when I accelerate slowly.
It's hard to tell whether it happens when I go full throttle because of all the noise and of course the tremendous g-forces the 400 produces.
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and of course the tremendous g-forces the 400 produces.
:bandit:
Have you checked for play on the swing arm?
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and of course the tremendous g-forces the 400 produces.
:bandit:
Have you checked for play on the swing arm?
Not specificly, but there's no play on the rear wheel and on the center stand when turning the wheel at 4500rpm in 3rd gear the wheel is rock solid.
Also a play in the swing arm should also be felt in 2nd of 4th gear...
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You are right, the chain and rear wheel will be moving the same speed whether in 2nd or 4th at that speed.
But the frequency the motor creates at 4500rpm combined with the frequency of whatever is not correct could combine to create the resonance issue, that is why it is only in 3rd gear.
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You are right, the chain and rear wheel will be moving the same speed whether in 2nd or 4th at that speed.
But the frequency the motor creates at 4500rpm combined with the frequency of whatever is not correct could combine to create the resonance issue, that is why it is only in 3rd gear.
It could... theoretically. However I tried 4500rpm in 2nd gear and 4th.
I also tried 50km/h in 2nd gear and 4th... so that resonance has to be VERY specific if it only happens in 3rd gear.
Also it happens at about 30-60 km/h.. so not that specific.
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Similar thing happened to my other bike - 1965 Jawa 250. I went to ride for maybe 20 km s, there have been short photosession with another similar machine and then we went home. Bike started to shake in 4th gear about 2 to 4 times per second. With my bike it was rather violent shaking and for sake of safety I finished my trip in 3rd gear (it has no 5th gear or above). Result was bent shifting fork for 3rd & 4th gear resulting in partially engaging two gears at the same time. When that happened the bike shaked resulting in the partially engaged gear to slip off and then again. At this place I have to make a note that this particular bike is notorious for problems with bent or worn shifting forks causing variety of shifting problems.
If your sprocket was worn I think you would hear *LOUD* whining from gearbox each time you engage 3rd gear. Even slightly worn and/or off axis sprocket (e.g. due to worn bearing) would make *A LOT* of noise at low RPM eventually getting less loud as the RPM raises due to rotational forces compensating misalignment.
My 6th gear sounds a little bit like this when it finally reaches some speed: https://www.youtube.com/watch?v=p1uchm4dOSg in low RPM. As the RPM raises above 6k there's is virtually any unusual sound. I've learned that it is caused by worn or out of limit bearing of 6th gear sprocket and the sound is caused by misaligned gearing contact patch. Some bikes have this condition but it looks like it does not tend to make any intermittent damage. I am checking oil for metalic parts and during last 12 000 km it is clean of any metal particles.
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If your sprocket was worn I think you would hear *LOUD* whining from gearbox each time you engage 3rd gear. Even slightly worn and/or off axis sprocket (e.g. due to worn bearing) would make *A LOT* of noise at low RPM eventually getting less loud as the RPM raises due to rotational forces compensating misalignment.
My 6th gear sounds a little bit like this when it finally reaches some speed: https://www.youtube.com/watch?v=p1uchm4dOSg in low RPM. As the RPM raises above 6k there's is virtually any unusual sound.
My bike has also started making a whining noise... but not in 3rd gear.. I think it's in 5th and/or 6th gear...
The shaking itself is not very violent. I can easily ride the bike without any problems or being afraid of it shaking apart... But at low speed it's definitely noticeable. It's like there's a small stone in my tire, or a VERY small dent in the rim like on bicycles.
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Check how 6gear motorcycle gearbox shifts. If sprocket pair engaged in 5th and 6th gear is at the same end of gearbox I would suspect one of axle bearings (but it is only quick tip and I am glad I didn't have to dismantle my bandit's gearbox yet).
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It's why I suspected the outgoing axle bearing.. But I can't find any play in it.. and it looks very solid when turning on the center stand.
Doesn't mean it can't be worn though... :stickpoke:
Perhaps it's the other axle... :yikes:
edit: i just looked at the diagram.. obviously both axles are in use for every gear.. so I don't see how a bearing problem could only show in 3rd gear.. I'm suspecting the 3rd gear sprocket or the 3rd/4th drive gear.
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Worn bearing IMHO wouldn't cause shaking. Shake means something has irregular shape and/or gets slightly blocked periodically. If sprocket was so much off-axis the whine heared when in 3rd gear would be hearable even on Moon.
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Mine also has a bit of a whine in 6th gear...
I think you posted the incorrect youtube link ventYl...
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I think you posted the incorrect youtube link ventYl...
Why? It makes exactly that noise at 0:35 :bandit:
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Oh! hahhaha
I watched the first 10 seconds of the video and was confused :rofl:
Ok cool, mine has a lower pitch than the one at 0:35
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Btw, when I tried setting the chain tighter.. the whining got MUCH MUCH worse, and it pretty much every gear.. but I figured it was the chain rubbing against the glider or something..
Now I think about it might have put more strain on the axle or bearing, causing that noise..
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I think you posted the incorrect youtube link ventYl...
Why? It makes exactly that noise at 0:35 :bandit:
Well, then I think it is time to inspect your gearbox. IIRC It should be accessible after removing oil pan with engine in frame. Wasting one day by gearbox inspection is better than wasting whole bike when something blocks gears while in motion. Gears are still available and the price is not killing.
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I think you posted the incorrect youtube link ventYl...
Why? It makes exactly that noise at 0:35 :bandit:
Well, then I think it is time to inspect your gearbox. IIRC It should be accessible after removing oil pan with engine in frame. Wasting one day by gearbox inspection is better than wasting whole bike when something blocks gears while in motion. Gears are still available and the price is not killing.
Hm, well on this board someone (Chris H) said you need to remove the flywheel and clutch first?
http://forums.banditalley.net/index.php?topic=13754.msg108953#msg108953
Does someone know exactly what needs to be done?
In the manual the gearbox is the last thing on the list on engine removal..
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-> shop manual
google knows where to get it
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-> shop manual
google knows where to get it
I've got the manual.. but it only says how to dismantle entire engine to get to the gearbox..
Or is there another manual?
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you just need to get a visual contact so check if before removing oil pan there are any additional steps affecting the engine (you have to remove output headers) and also if removing oil pan will get you a visual reach to gearbox.
this should be deducible from pictures in shop manual
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VentYl is right, taking the oil pan off gives you a pretty good view up into the gearbox. I used this method to inspect the gearbox of my fuel injection project bike.
The only drawback is having to look at it upside down from underneath the bike. I used a combination of items to do my gearbox inspection: I used a mirror for general looking and a USB boroscope hooked up to my computer for the fine detail looking.
I was able to thoroughly inspect every cog and dog in the gearbox. I wasn't paying close attention to the bearings though so I don't know if they can be viewed easily with the mirror or boroscope.
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VentYl is right, taking the oil pan off gives you a pretty good view up into the gearbox. I used this method to inspect the gearbox of my fuel injection project bike.
The only drawback is having to look at it upside down from underneath the bike. I used a combination of items to do my gearbox inspection: I used a mirror for general looking and a USB boroscope hooked up to my computer for the fine detail looking.
I was able to thoroughly inspect every cog and dog in the gearbox. I wasn't paying close attention to the bearings though so I don't know if they can be viewed easily with the mirror or boroscope.
So you can just remove the oil pan without removing anything else?
Then what did Chris H mean in the other topic?
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Yes, if your intent is to merely inspect/troubleshoot the gearbox then viewing it from the bottom after removing the oil pan is the way to go.
Because I was refurbishing my entire project bike I did this: With the bike up on stands (front and rear to get it up in the air and stabilized so I could put my head under the engine), drained the oil and then removed the oil pan. Once this prep work was done I began inspecting the gearbox.
I also removed the chain and the countersproket so I could spin the gearbox without the extra noise of the chain clacking across the countersproket. I used a rubber coupling and a cordless drill to spin the gearbox when I wanted to listen to the gearbox bearings. A "mechanic's stethoscope" is a nice thing to have/use when you're trying to determine if a bearing is good or bad.
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VentYl is right, taking the oil pan off gives you a pretty good view up into the gearbox. I used this method to inspect the gearbox of my fuel injection project bike.
The only drawback is having to look at it upside down from underneath the bike. I used a combination of items to do my gearbox inspection: I used a mirror for general looking and a USB boroscope hooked up to my computer for the fine detail looking.
I was able to thoroughly inspect every cog and dog in the gearbox. I wasn't paying close attention to the bearings though so I don't know if they can be viewed easily with the mirror or boroscope.
So you can just remove the oil pan without removing anything else?
Then what did Chris H mean in the other topic?
Almost forgot... I think you may also need to remove the oil pickup after you remove the oil pan. I remember doing that too but can't recall whether it was due to gearbox viewing or "just because it was there". Either way it's easy to remove and replace.
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Another "also": Over the last few days I was reading this thread and giving it some thought. I was intrigued by your description, that it was noticeable in one gear and not in others.
The only thing I could come up with was this: In a standard 6 speed Constant-Mesh motorcycle gearbox you have two shafts, the "drive" and the "driven". This entire assembly turns (is carried by) four bearings, one at the end of each shaft. You would think that if one of those bearings was going to make noise it would do it no matter what gear ratio I engaged.
But while thinking about your problem I began to wonder if that's not true because when you select different gears the vector of force within the gearbox changes. There are some good demonstration videos of motorcycle gearboxes that are posted up on YouTube that you can watch to see this. With every gear change the path of power transfer through the gearbox also changes. Each of these unique pathways has its own unique vector of force and that vector will affect the four bearings that support the gearbox differently.
This might explain your experience with the sound/vibration/thrumming feeling.
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And... Good luck with this problem, we're all pulling for you.
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But while thinking about your problem I began to wonder if that's not true because when you select different gears the vector of force within the gearbox changes. There are some good demonstration videos of motorcycle gearboxes that are posted up on YouTube that you can watch to see this. With every gear change the path of power transfer through the gearbox also changes. Each of these unique pathways has its own unique vector of force and that vector will affect the four bearings that support the gearbox differently.
This might explain your experience with the sound/vibration/thrumming feeling.
Bit of a late reply.. I haven't done anything to the bandit all winter (busy on GPZ900 and GSX600F) .. but this sunday I replaced the oil and filter and went for a spin. There wasn't any hard metal or aluminum on the drain bolt or on the inside of the thread.. so that's good.
The shake/thumb is still there though. I thought about what you said, and I can understand it happening only in one gear by way of unique vector of forces etc.. but do you really think it could be so specific that it can only happen between 4k and 5k rpm.. and not at 3k or 6k rpm? The vector of forces would apply throughout the entire rev-range. Only maybe some specific resonance could explain it but I find it very hard to believe... :stickpoke: