08 cbr125r vibration

Old 07-08-2012, 07:14 AM
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Join Date: Dec 2011
Posts: 10
Default 08 cbr125r vibration

well seeing how there isn't much written info on this bike and by much i mean zero. i figured I'd just ask here. So were to begin, I've got an 08 honda cbr125r and I've recently done the 14tooth front sprocket mod. now when I'm riding and i pull i the clutch lever I'm getting a very mild vibration in the foot pegs. it almost feels like I'm rolling over some small rumble strips but its very small, now on this note i'm note going to hide anything here. i run this bike hard i can't recall a time i don't have this thing red-lined and i manly use engine braking, also when i swapped out the front sprocket i noticed that the new one isn't sitting very good it has some sliding motion to it of about a quarter inch. i'm not sure if that because its the wrong sprocket or what but its there. and as a sresult every once in a blue moon I'll get a jump int he chain but as soon as i let of it goes away. i've set the chain tension to 3/4 of an inch. per spec.so any tips or advice would be great. I'm also noticing some strange sounds such as plastic rattle when riding and some noise from the rear sprocket when i'm rolling with the clutch in. the bike has 5500 km. on it and i;ve done my oil change and cleansed the chain once since i got it. it had 1800 on it when i bought it in December.
Old 09-20-2012, 10:19 PM
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Join Date: Sep 2012
Posts: 9

Where to start? I work on these and other bikes here in Brasil all the time. I don't need to tell you that there are thousands of possibilities for vibration. But let's start with assuming it all started after the sprocket replacement... Whenever you replace a sprocket, you should ALWAYS replace the chain and other sprocket. different wear patterns etc. Now keep in mind that the "play" you are talking about is NOT normal and often comes from poorly made replacement parts (ie: incorrect material size or thickness). This is normally resolved with a wave-plate styled washer, or the standard washer provided stock. Check to ensure the sporcket is installed correctly and lined up in the shaft-teeth well. If you still have play then I would suggest you go to the wave washer or replace the sprocket with a better manufactured one.
The noise from the rear sprocket is normal when the chain binds up as it comes over the top. If your chain is adjusted as you say then I would replace the chain because it is likely the links are worn and binding (cleaned and oiled or not).
I always tell my clients to modify ONLY the rear sprocket to avoid clearance issues with front sprocket and also because the adjustment is easier at the rear. For instance a 42 tooth rear and 12 tooth front... if you add one tooth to the front you will need to take of two teeth at the rear to equal it. and the opposite of course applies. The adjustment at th rear is easier and has more fine adjustment.
With this small bike I would suggest buying a complete set of gears and chain with standard front and adding 2 teeth to the rear. You will have more torque but less top end. run plugs 1 stage colder if you run high RPM's alot. Dont run open pipes or knock out the baffle either... will hurt your low end torque. Also take some time to consider tire size... height and width. Height affects the rotation as much as the teeth on a sprocket. Width adds friction to the ground, and although it looks cool, wider tires really put a hurtin' on those small CC bikes.
Hope this helps...
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