KymcoForum.com
General => Technical | How To => Topic started by: laladownunder on January 15, 2017, 01:40:28 AM
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My 50 cc Kymco Agility gy6 4t got 13,000 kilometer. Done all the upgrade de restriction mods and going fine for about 7,000 kilometers. On the way to work just started to vibrate, no vibration when idle, only when picking up revs, done whole exercise without belt and still vibrating, changed timing chain tensioner with new longer shaft tensioner. Still vibrating, sound seems to come from bottom on variator side of motor block. I opened tappid cover and turned engine over by hand to check timing chain for broken links, but none broken, still vibrating, Also put in new sliders in variator, still vibrating. I got new Timing Chain, guides, tensioner, complete gasket set. Need help/idea where to go next.
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Engine mount?
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Thanks Mr Paul, As solid as can come, vibration sound seems inside
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Also removed the belt, which eliminate drag and rear end vibration ( if any ) Still vibrating when reving up
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See if you can move crankshaft with CVT belt removed. That's up, down, fore and aft. Should be no movement.
Karl
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Thanks Karl, done that and no up, down or sideways movement. also took the tappid cover of and started motor, oil everywhere, so oil pump working. Checked the timing chain again with the new longer timing chain tensioner and no extra movement on chain. touch the variator and immediately the cam moves.Also started motor with no variator disk and roller weights in, only the outside gear where starter pinion runs on, still vibrating.
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Have you checked the spark plug.? A misfire can cause a shutter. Is the vibration harmonic or erratic?
Also might try removing the valve cover and rotating the engine to make sure the valves are moving and not sticking. Hope you can isolate the problem.
Mac
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Are there any missing blades on the variator fan? Also, please explain what you mean by "touch the variator and the cam moves."
Karl
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Also removed the belt, which eliminate drag and rear end vibration ( if any ) Still vibrating when reving up
Include spark plug cap inspection (http://www.kymcoforum.com/index.php?topic=23040.msg164524#msg164524) in your troubleshooting.
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Karl, wouldn't stuck sliders in the variator throw it out of balance?
Mac
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Best way to find where the sound is, is to get a mechanics stethoscope and listen if you can't get one of those find the longest screwdriver you have put the metal end on the bike and the other end on your ear
Usually it goes like this
Deep internal rumble: Crank or big end bearings
Taping in the head: valves or tensioners or an exhaust leak
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After re reading your post I'd check the oil see if you can see any metal
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Stuck sliders/rollers would do it, Mac, fer sure! Good point.
Karl
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Yelp, the stethoscope will tell you where the noise is. You can get one from Harbor Freight Tools really cheap. Good idea. You will get "some" noise from any where on the motor, when it,s running, but it's the louder noises you are looking for. You will know when you hear them. Good luck.
Mac
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Hi Mac, the vibration is harmonic and using a big screwdriver, seems noise is on variator side. I run engine without the internals of variator, no weights and pulley, just the outer pulley/ gear where starter motor kicks in for starting
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Hi Karl, I meant, that with the timing chain and new tensioner in place, if I turn the variator by hand there is instant movement on the cam. Checked the blades on variator and all the blades in place. I told a friend about what you said, move the crank up, down and sideways, He reacon that even that I could find no movement, it can still be the crank bearing in the block ( split casing in this case ) on variator side that worn away the bearing hole / seat just slightly now causing the outer race of bearing to actually turn in the casing. When idling, no vibration, when revving up it start vibrating. He even recon that there is maybe nothing wrong with the bearing, it just ate away the alum casing. What u recon ???
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Sounds like it is time to completely dis-assemble the engine and inspect everything.
Karl
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maybe nothing wrong with the bearing, it just ate away the alum casing
Unlikely . . crankshaft and connecting rod bearing failure is typical with 139QMB big-bore-kit installations, but somewhat rare for stock 50cc's.
http://youtu.be/H5hdqSGeiGE (http://youtu.be/H5hdqSGeiGE)
http://youtu.be/vlYkHVErP5s (http://youtu.be/vlYkHVErP5s)
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Now this is coming from a older mechanic I am honestly not to familar with this scooter but the usual assumption if there is any vibration on the crank its a bad bearing knowing that don't run it anymore even if it is not it pays to be careful better that then paying for a new crank
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Thanks Tortoise, with no up down side way movement, I still think it to be the crank bearing, it just started and I have not driven it again, just fishing out to what might be the problem.
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Hi, thanks Karl, yup I am going to do it this weekend and hopefully it is only the bearing
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star667, I tend to agree with you and will strip it this weekend, Lucky I did not continue riding it when vibration started and hopefully it is just the roller bearing
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Thank you for everyone making an effort to help me. I think I am on the right track now and will not strip the engine for nothing, must be a bearing. Thanks
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Don't take too long. I am holding my breath to find out what you find in that thing!
Karl
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I bet bad bearing
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Well, here we got it. It is the bearing on the variator side. Seems a bid of a grind - very softly - but enough for me to replace. Also there is ringmarks on outer racer indicating the bearing was turning in the seat/ hole. Will have to get a new crank as it seems like one hellofa job replasing bearing and will have to knurl the bearing seat/hole for a tap in fit - now both bearing slide in and out with hands only.
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Don't forget about a Loctite product called "bearing mount" for just such an occasion as yours. I used it years ago on a SAAB transmission and it worked perfectly! Inside knurling is nearly impossible to find a shop that has the tooling. Need the whole crank just for the bearing? Gotta be some way to get that thing off.
Karl