What Causes Vibration In A Motorcycle Crankshaft?
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- Опубликовано: 29 авг 2024
- Cycle World Technical Editor Kevin Cameron answers your motorcycle engineering and mechanical questions. In this episode, many people have encountered “elephant-ears-flapping” crankshaft vibration. Kevin explains why it’s happening in every engine all around us.
I want to talk about "elephant-ears-flapping" vibration in crankshafts. That wonderful description comes from Cycle World's Italian correspondent Bruno dePrato, who was speaking of vibration that can occur in crankshafts. Here is an example of a two-stroke crankshaft, but this movement can also happen in four-strokes.
In this case, a pair of flywheels is joined by a crankpin that is pressed into the two flywheels. These two flywheels are constantly being accelerated by combustion pushing down on the piston. The result is the two flywheels vibrate toward and apart from one another, as Bruno puts it, like elephant ears flapping.
This system of two masses and a crankpin is reduced in frequency by adding the mass of the ignition rotor. When the Yamaha RD400 came out, it had larger and heavier flywheels. Therefore, they vibrated at a lower frequency. When the mass of the ignition rotor was added, the vibration was considerable.
A discerning racer coming home from a weekend at the club races took off the cylinder and put a feeler gauge between the flywheel and the connecting rod. Instead of the usual 0.017 to 0.018 of an inch, he found the clearance had increased to 0.024. He went to another club race and when he came home 0.024 had become 0.028.
Here’s what was happening: The ignition flywheel was slowly walking off the crankpin. With the extra mass of the ignition rotor, the elephant-ears vibratory mode was slow enough to come into step with the engine’s firing frequency. The bearings were not enough to completely prevent this vibration.
Eventually his crankshaft would have gotten so much wider that it would crowd the bearing between the flywheel and ignition rotor and then destroy it. Many people have encountered this charming elephant-ears-flapping crankshaft vibration. It’s happening in every engine all around us. Most of them manage to survive it, but occasionally there is a failure.
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When it comes to the ability to communicate technology, Mr Cameron leads the way.
These tech videos are absolute gems. Kevin is my hero.
Kevin Cameron's grasp of physics and his talent for communicating his understanding in a manner accessible to the rest of us is remarkable. That's why I jump at any opportunity to read or listen to his explanations at any chance I get. He does great work, and it's always enlightening and enjoyable. He's the best.
Excellent. I wish the car community had someone like you.
Every one of these episodes is very interesting, and I feel I learn something new each time. Thanks
I raced a '77 RD400(434cc) in 1983-84 and it was common practice to weld the crankpin to the counterweight. I broke a lot of parts, but never had a crankshaft failure of any sort. If I had a real budget I might have done something different, but welding and breaking the cases to check bearings every 200 laps(1.8mi course) worked well enough.
I find, much like MEs(I'm an EE) that continued success yields little knowledge, while failure drives processes forward.
This is true in any endeavor where sustained effort and increased efficiency is desired.
Thank you, 40 years after I production raced a rd 350 and then later a rd 400, you explained what we could never get a handle on, who thought the crank was flapping like a harley? Not any of us, we blamed everything else.
Did the 400 have more vibration than the 350?
@@RealAutoReviews yes, quite a bit more
@@williamrusk631 whoa!
Best start of 2018 tech videos :)
I absolutely love your videos. Keep 'em coming!
What we want?
Kevin's Channel!
When we want it?
Now!
im probably dealing with this on my nsr 250 two stroke. at 7k rpm you can feel and hear it and thats with sending the crankshaft to a alignment and balance shop.
now sir i ride a bike but i dont know what is happening inside it thanks to you and that link i clicked will watch more.
I think I have asked this in another video. My interest in motorcycles started in the early 1980's when Kevin still worked at Cycle. Back then, the GS and GPZ1100s ruled with their "pressed together roller bearing crankshafts." When these bikes were hot rodded way past their stock 104 horsepower, their cranks were "welded" for greater stiffness. This video shows an excellent view of one of these cranks with their counter weights in very close proximity to precision roller bearings. How the heck does one get weld in there to make them stronger?
I'm not an authority on the subject, but I assume the entire journal is hardwelded and then turned back down to size. So it's not just the joint that gets welded, it's the entire width.
Seems like an immense amount of trouble. Re-watching the video, trying to figure out where to stick the welding rod. You're right, there has to be some turning involved. Still have a copy of Motorcyclist from... 1983? The crew of Motorcyclist built a GS1260 out of a Suzuki GS1100. They had its crankshaft welded. They said it was now "lighter, straighter and stronger than any stocker." It had lost 1 1/4 pounds. They also retrofitted a GS750 oil pump into it. The 750, at the time, had a one piece crank with automotive shell bearings, like any non-Harley street bike has today. The GS750 pump was considered an upgrade for their new 1260. Maybe that was the best upgrade. It speaks to how obsolete pressed cranks have always been.
What can I write? Awesome and brilliant as always. Thanks Kevin. Happy 2018. Greetings from Brazil.👍👍
I thought the explination was ok but it would have been nice to get more into frequencies and also have some visuals of the vibration while the crank is in operation. I know it's a lot to ask but still it would have given people an even better comprehention.
I do really love these videos but what’s with the creepy choice of music? I keep thinking I am going to see a haunted doll pop up in the background... Hard to concentrate on the lesson when you keep me on edge like this :)
I enjoy sll of your videos.
Nice work dad!
Very nice explanation. Congrats.
Sir, do we increase (in some extent ) Torque as well as HP of any four stroke fuel injected motorcycle and if yes then How
Is that why my right pag is vibrating above10k rpms? Just got a new 2017 r6 and after the break in period I noticed the vibration,
.
How about its caused by bushing or mounting? And How about vibrates and wobbling on handlebars?
Hey Kevin, did you ever know T.C. "Tommy" Brown when he was a rep for Honda motorcycles in the early days of their presence in the USA?
What about out of balance con rods or pistons, or worn crank bearings and big and small end bearings, they also make the crank vibrate?
WELL SAID.. love youre video and KNOWLEDGE thumbs up your WAY. you taught me somethig i didn
Good day to you. I'm a custom bike shop, that produces oldschool thumpers from 500 ccm upwards.
Today I have a customer that wants a motorcycle with a Neander crankshaft system thumper.
We have the problem, that this is our first time planning our own engine and we wanted to ask: this 1400ccm thumper is getting 2 iron cast crankshafts. As they can't be affected by this as in your story, will there be other breaking points that make their play furthermore?
Thank you in regard
Alexander Borrmann
BORRMANN MOTORCYCLES AUSTRIA
That, I didn't know- thank you :-)
Love your videos so much wisdom .
my motorcycle engine excessevlely vibrate from accelerating even before reaching high rpms and it doesn;t smooth out it keeps vibrating you feel like the engine is going to jump.
Sir ..how are you ..?? Why u not making videos anymore
Hi.. Sir My YAMAHA RX 135 4speed a lot of vibration what is the reason.?
Crank laith work's done then fitted the engine
sir ...does that mean single piece crank does need weight on ignition rotor??
my gixxer bike is vibrating at 32kmph in 4th gear and at 40kmph in 5th gear after that point it stops vibrating it vibrates only at 25, 32 and 40 kmph in 3rd 4th and 5th gears respectively what may be the reason? plz
You are lugging the engine 🤦 It's a 250, not a 150. You shouldn't be doing low speeds in high gear.
How do you get the con rod on with a solid crank? My guess is they are pressed on and then welded solid... or?
vincent was a 4stroke..2 piece rod. and i have seen them tack weld the pin to the flywheel on 2 strokes with 1 piece rods
you need a 2-piece con rod, the big end is split so that you can attach it to the crank.
i have never seen a con rod with end cap used on 2 stroke reed valve motors.
fair enough, I'm not that familiar with 2-strokes
...Roller/needle bearings don't do well with the joints in a 2 piece rod/cap....
Hey i have some problem how can I fix need help
Hello Kevin, having raced a RD400 for many years back in the late 70s to mid 80s, I had to have a lot of cranks rebuilt and collected a lot of broken and bent bits and pieces. I even went to the extent of replacing the stock transmission and clutch assy with one from a TZ350 so I could use TZ roller bearings on the outside of the crank to minimize it's walking back and forth in the cases. I found the close ratios of the transmission and the primary drive didn't exactly meet the needs of the slower turning RD400 crank. I've always though about going rebuilding it back to stock again as it was more practical for classes I ran in and easier to ride but I'm too old now to worry about it. Anyone interested in a complete, "almost new" TZ350 cr transmission and clutch assy with straight-cut gears?
HD
Kehna kya chahte ho!!!!!!!