Bent Sprocket - Advice Desired

[rfmueller]

A while back I pulled the wheels for tires replacement, but in the process, I let the rear wheel fall over on to the sprocket  , had the tire changed, then forgot about my error.  Well, I'd been wondering why my gas mileage dropped by 6mpg as well.  The other day I put the rear wheel up on the jack and did and oiled the chain, and checked the sprocket run-out:  It was huge; like a millimeter!  Ran the rear wheel and that chain rattled back and forth like nobodies business.   Well, I'd put about 300 miles on those tires since re-installing them, so besides the obvious rear sprocket needing to be replaced, I'm wondering if the chain and front sprocket should also be replaced.  The front sprocket looks bran new, and that's partly because I keep the chain wet with great heavy chain oil, and the chain itself hasn't stretched.  It appears fine.  Yet, I'm still wondering if replacing some or all of it would be a good idea.  The difference is that the chain/front sprocket/nut/30mmsocket/chainbreaker makes the price another $180 on top of the $45 rear sprocket.

Any words of wisdom out there?

 

[klx678]

I would look at the front sprocket for any crazy wear, if it was okay then I would just replace the rear sprocket. 

[randy2100]

Front sprocket should be fine.  If the chain doesn't look worn, then it's probably OK.

[rfmueller]

KLX678 & randy2100, thanks for the input.  

All, please keep them coming, especially the motorheads.

[DewMan]

Are you seeing 1mm or 1cm? 1mm is less than 4/100th of an inch. 

Chain tolerances are not tight enough to have an issue with only 1mm of run out IMO.

[cornerslider]

All due respect.... I it would be highly unlikely that a wheel falling over on the sprocket would bend it. What most likely happened in the the "cushions" in the cush drive shifted slightly. Maybe remove the wheel and be sure the cush drive isn't shifted, or binding somehow.  I also agree with @DewMan, 1mm of run-out is nothing-

[DewMan]

9 minutes ago, cornerslider said:

All due respect.... I it would be highly unlikely that a wheel falling over on the sprocket would bend it. What most likely happened in the the "cushions" in the cush drive shifted slightly. Maybe remove the wheel and be sure the cush drive isn't shifted, or binding somehow.  I also agree with @DewMan, 1mm of run-out is nothing-

I agree with @cornerslider. I suggest pulling the rear sprocket and laying it on glass or some other known flat surface to check for runout with a feeler gauge as a first step. That'll cost you nothing. 

Good luck resolving your issue.

[mossrider]

Fa getta boutit.

Have a friend help you and run that rear wheel in the air with some load on it from the back brake. It'll take a little coordination but get get it up off idle, 2nd gear - maybe 15 mph. Now get down there and watch the business. Much of that chain noise and snatchety crap will disappear. I doubt you'd be able to notice that kind of run out but if you do and it bothers you, you can sure put a chain on it if you want but unless there's something else going on there you'd be hard pressed to convince me you needed a chain let alone sprockets.  

You wanna double your money? Fold it in half and put it back in your wallet.

$.02

[klx678]

I defer to those with more experience and seen more than I have.   

[rfmueller]

Thanks for all the tips and input, ya'll.  I'm going to do all that testing tomorrow before work .        Wish it wasn't going to be colder than Siberia so I could ride it work.  The new sprocket arrived today.  

[peteinpa]

You did not bend that sprocket.  Couldn't do it throwing it from 3 stories up.

Running the bike in gear with the wheel off the ground will be noisy, snatchy,and jerky, that's normal.

You already ordered a sprocket? Save it for much later.

If you are going to do your own maint. and ride and own bikes well into the future, start buying tools. They will pay for themselves MANY times over.

Edited April 2, 2020 by peteinpa

[rfmueller]

@ Cornerslider:  I got as far as pulling the sprocket off the original rear sprocket:  It's perfect.  On the bike, the runout is just over a mm, but on a flat surface, it's better than the new sprocket!  Further, the original OEM is in perfect condition; there's hardly a scuff in any of the teeth.  

So I began re-assembly and according to the torque specs, the sprocket nuts get 58 ft lbs of torque.  That seemed a bit high, but that's what the spreadsheet said.  It stripped out all the nuts.

[fzar]

2 hours ago, rfmueller said:

It stripped out all the nuts.

Confused here, What do you mean stripped them out?

 

[rfmueller]

In the interest of bringing the sprocket down evenly, the proper way to snug them down is a little at a time like you would do with a tire replacement on a hub.  (Well, at least back prior to the 1980s), so as I was using the trusty torque wrench, bringing them down a stroke at a time each, well..... they sort of never tightened up.  The nuts stripped out.   Two of the nuts while removing them, also pulled the bolts out.  The threads were full nut metal.  I'm replacing those two bolts, and all of the nuts.  Just hope I can find them at the hardware store.  Yamaha wants too much money.  EBay would be okay except for the $10 shipping charge and the wait.

"Just keep tightening til you hear that first 'click'; you're there.  Stop."  

[fzar]

Any pics?

[rfmueller]

Sorry no pics.  Wish I had more time to play with it.  The Corona virus has made a lot of extra work for me.

[fzar]

I had an issue with the studs as I tried to get the sprocket off, they started spinning out. I just took them out and reinstalled them with red loctite. Here:

[rfmueller]

I just found a thread from a different forum that reported the same issues with the rear sprocket torque.  Apparently the real spec is 30NM (22ftlbs), but the writer didn't specify where he got the spec.  It makes a lot more sense than 80NM (58ftlbs).  When I get new studs I'm going to do the red Loctite deal as shown in your pic.

[DewMan]

FYI: Whether it's correct or not I used the Service manual which states 58 lb-ft of torque when I did my 520 conversion and had no issue. I could have just gotten lucky though.

[rfmueller]

This is painful.  My bike has been down for a week, and it's going to be at least another week before the parts get here.    I'm trying to look at the bright side.  The weather is mostly cold and rainy, and I have to work a ton of OT because of the Corona virus.  And, I don't have the Corona virus.     

[fzar]

53 minutes ago, DewMan said:

FYI: Whether it's correct or not I used the Service manual which states 58 lb-ft of torque when I did my 520 conversion and had no issue. I could have just gotten lucky though.

Thats what I did, I had no problem with the red loctite,( I let them sit for 24 hrs) 58 ft/lbs seems a little much but it worked for me too doing 520 conversion.

[cornerslider]

2 hours ago, rfmueller said:

In the interest of bringing the sprocket down evenly, the proper way to snug them down is a little at a time like you would do with a tire replacement on a hub.  (Well, at least back prior to the 1980s), so as I was using the trusty torque wrench, bringing them down a stroke at a time each, well..... they sort of never tightened up.  The nuts stripped out.   Two of the nuts while removing them, also pulled the bolts out.  The threads were full nut metal.  I'm replacing those two bolts, and all of the nuts.  Just hope I can find them at the hardware store.  Yamaha wants too much money.  EBay would be okay except for the $10 shipping charge and the wait.

"Just keep tightening til you hear that first 'click'; you're there.  Stop."  

This is an area I would not use "hardware store" bolts...... If those replacement bolts were to fail., I would think it would end VERY poorly. I'd go OEM Yamaha studs-

[fzar]

2 hours ago, rfmueller said:

When I get new studs I'm going to do the red Loctite deal as shown in your pic.

I'm not a mechanic or do I know if its the right thing to do. To give you the full story in a short version. I had a rear wheel bearing problem that I had to disassemble the rear sprocket, when i fixed the bearing problem I used blue loctite on the nuts when re assembling. 1K mile later I had to replace the chain and sprockets, at that time the blue loctite I had used overpowered whatever was used from factory in the other end of the stud attached to the hub. Thats why they backed out. The factory stuff looked green!!! All I'm saying is (I did what worked for me)

[D.A.]

I changed the rear sprocket on my FZ07 about a month ago. Up until then the original sprocket was still in place. I bought the bike used and the previous owner had neglected the chain. The bike only had 5900 miles on it but the chain and front sprocket were covered with rust. The rear sprocket was fine but I nonetheless decided to replace the whole kit and caboodle.

I had to use a breaker bar to loosen the rear sprocket nuts, which suggests Yamaha had torqued them down to a relatively high setting. 58 ft lbs does seem like overkill for an M10 bolt but that's what my factory service manual specified so that's what I used when installing the new rear sprocket. And like others here, I never had any issues whatsoever.

RFMueller: Any chance your torque wrench is inaccurate and that you inadvertently over-tightened the nuts to the point they stripped?

Also, I feel bad for you: You started this thread about a bent sprocket possibly causing you to lose 6mpg and ended up with stripped bolts and nuts!

[klx678]

Here is information from The Engineering Toolbox:

 

Does seem crazy tight, but done in increments, should be possible.   Do it in several steps, using a cross pattern with a clean dry bolt, no lube.  Using LocTite 242 blue would make sense and they claim no change in torque.    I'd do 10 - 20 - 30 - 40 - 50 - 58. 

One other choice, safety wire drill the nuts, tighten to maybe 40 ft-lb and wire it.