17T Sprocket vibes?

[petaminox]

Hi guys,

I just installed a JT 17-tooth front sprocket (what blasphemy) in hopes of lowering my RPMs on the highway as that's where I'm mainly on. Everything's real kosher, but my FZ seems to have developed a weird vibe.

In 4th gear, travelling between 65-75 km/h, the bike develops a pulsating vibrating felt most strongly through the foot pegs. It almost feels like the chain had a tight spot and was scrapping something.

However, I doubt it is the chain for two reasons. First, travelling at 65-75 km/h in ANY OTHER GEAR does not produce said vibrations. Second, swapping back to my 16-tooth sprocket removes the vibration.

I have tried cleaning and lubing the chain, aligning the wheel, checked the sprocket installation and such without any luck. I've also read somewhere that this may be a product of harmonic vibrations... Anyone else have had such an issue, and perhaps a solution?

 

[major tom]

I've installed two of 17t sprockets with no problems. I actually own two FZ6's. Sounds like there is a specific flaw in yours, like possibly the mounting splines, the hole, is not concentric with the outside circumference.. Does your chain slack vary as the wheel is rotated? Don't install the CS cover and rotate the wheel if slack varies with one CS sprocket rotation that could be your problem. Funny though it only occurs in 4th. My next ride 65-75 km/h= about 42-45 m/h, I'll check. Though it cant be bad as I think I would have noticed.

 

[petaminox]

The chain slack varies ever so slightly, but isn't this normal for chains? After all when adjusting chain slack it is practice to ensure measurements are taken from the tightest part of the chain to the swingarm.

I contemplated if the 17T sprocket was defective, but figured that if that was the case the vibration would happen at the same speed, regardless of the gear I am in.

Thanks for checking!

 

[TownsendsFJR1300]

Agreed with both your and Tom's posts above.

I have to lean towards checking the mounted, 17 tooth sprocket to make sure there is NO manufactuing defect.

Just mounting, say a wire coat hanger tip, super close to the ft sprocket and looking for wobbling (and actually, the valley of the teeth) wouldn't hurt.

And yes, there will be some tightness/looseness in a chain with normal wear and tear.

Just curious, how many miles on the chain, well maintained its life, etc??

Also, what are the RPM's the new vibes/issues are happening at?

Just for S&G's, check the engine mounts (all including the rear, long steel bolt/nuts) that their all at 40 Ft lbs.

**Not mentioned but extremly important, is the chain slack approx 2" TOTAL UP and DOWN at its tightest spot? The vibes coming thru the footpegs is usually attributed to the chain either being misadjusted, worn or NOT lubed/maintained..

 

[iSteve]

Using a new sprocket with a old chain may also contribute to this.

 

[FinalImpact]

Engine loading and RPM affect drive train throughput. That said, most chain / final drive vibration related vibes Begin around 40mph (65 km).

My vote goes towards the sprocket not being uniform or perhaps 100% true. Like Scott said, find a way to measure it. We could be talking about a very tiny variation. Like something less than 0.005" width or height variation...
Good luck.

Ps - just curious, what are you trying to gain? Fuel economy or ????

 

[major tom]

Final impact, I have experienced improved MPG on both my FZ6's, 2-3 at least, but more importantly my cruising speed has increased without vibration and now my speedometer reads right on-not the ODO though so I have to do mental gymnastics to figure my true MPG. I'm now confident if I go 5-6mph over the posted limit I will not get a ticket and I need all the help I can get in this regard. My detector helps too. Best regards.

 

[ratrider45]

Using a new sprocket with a old chain may also contribute to this.

:Flip: check the cush drive in the rear wheel hub when i got mine i had to mess with it as the rear sprocket wobbled from side to side.make sure there are no aluminum casting flaws in the wheel hub and that the cush drive rubber pieces are concentric.if yours is off just putting bike on center stand and rotating the wheel will give up the ghost

 

[FinalImpact]

:Flip: check the cush drive in the rear wheel hub when i got mine i had to mess with it as the rear sprocket wobbled from side to side.make sure there are no aluminum casting flaws in the wheel hub and that the cush drive rubber pieces are concentric.if yours is off just putting bike on center stand and rotating the wheel will give up the ghost

Whaaaa????

OP installs a FRONT sprocket and did not touch the REAR SPROCKET! Besides; cush drive rubbers will squish when the axle is tightened unless turned 90°...

 

[TownsendsFJR1300]

:Flip: check the cush drive in the rear wheel hub when i got mine i had to mess with it as the rear sprocket wobbled from side to side.make sure there are no aluminum casting flaws in the wheel hub and that the cush drive rubber pieces are concentric.if yours is off just putting bike on center stand and rotating the wheel will give up the ghost

As Randy noted above, the rubbers shouldn't make a difference (as long as their properly installed). Just as a side note, when I have the sprocket hub off for what ever reason, I'll make sure the rubbers are clean and actually spray them down liberally with silicone. Probably not necessary, but I don't want any binding and have them slip in W/O issue...

Any rear sprocket wobble is usually attributed to the bearing lightly pressed in the hub going south or a bent axle..

I had both fail on my old KLR 250, ever so slight but the sprocket definitly moved in and out (about 20,000 miles on at that time). And the bike was used strictly in the street. I think two up and jumping curbs did it in..


For the OP, just to confirm, with the larger front sprocket, you did re-adjust the chain correct? (as it would have tightened up with the larger front sprocket)