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I tried all the the nuts to see if I could get any to budge. I got a few to spin, but the bolt also spun. And when I put an Allen key on the bolt that just rounded off the bolt head. I ended up grinding the heads off. I wouldn't even recomend anyone try anything other than grinding off the heads, as its seems like a waste of time.
It was 4pm on a Friday and the the replacement bolts would be a special order item (maybe 4 business days wait). So I bought 8.8 steel structural m10 x30mm bolts with nylon locking nuts and red lock tight.($20) Both the nut and the bolt have 17mm heads and the nut doesn't have the metal locking plate that makes it impossible to get off. So in future it should be removable with out too much pain.
New Michelin street 2 tire
Cbr300r sprocket kit 14t/36t
X-ring chain
I'm midway through painting the lettering white with acrylic paint
I think grinding is the best way. If you are replacing the sprocket anyway, grinding the head off of the bolt is easy because you don't need to worry about messing up the sprocket.

If you are using nylock nuts - you don't need the Locktite. Red Locktite is a bit much for that, and usually requires heat to remove. Nylock nuts alone should be adequate without any (blue) Locktite.

That chain looks kinda taught from the photo. Have you spun the wheel to confirm you made the adjustment at the tightest spot? It may change a lot, and you need to set the slack where it is the tightest.

Having the chain slightly loose is better than slightly tight.
 

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Yea, no need for extreme locking. Why make extra work for yourself next time?

There's very little lateral load from sprocket on these bolts, so very little force on nuts. It only requires enough clamping to generate sufficient friction to transfer power across to spocket carrier. On bigger bikes, many uses smaller hollow 8mm bolts for this application. Similar to brake-rotor bolts in front. Which faces much, much higher loads.
 

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If you are using nylock nuts - you don't need the Locktite. Red Locktite is a bit much for that, and usually requires heat to remove. Nylock nuts alone should be adequate without any (blue) Locktite.

That chain looks kinda taught from the photo. Have you spun the wheel to confirm you made the adjustment at the tightest spot? It may change a lot, and you need to set the slack where it is the tightest.
@DannoXYZ

I was a bit worried the vibration or something would work the nuts loose, its good to know I over did it lol. I can just heat the locktight with a torch for 30 seconds and those nuts will come right off. Also my previous sprockets were 12,500km and had almost no signs of wear. Im guessing with my use, I will get around another 25,000+km before these need to be replaced. The only reason I changed them this time was because the chain had many many stiff links from basically sitting for 8 years.

On the swing arm it says adjust so the play is 25mm(1") and that is what its set to now. It does look tighter than I previously had it. Ill keep an eye on it
 

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I tried all the the nuts to see if I could get any to budge. I got a few to spin, but the bolt also spun. And when I put an Allen key on the bolt that just rounded off the bolt head. I ended up grinding the heads off. I wouldn't even recomend anyone try anything other than grinding off the heads, as its seems like a waste of time.
These screws are not opened with an allen key, it is a TORX KEY(star key), and the size is T45.
https://www.tooled-up.com/ LINK
Hood Font Symbol Tool Circle

The torque on the screw heads is smaller, so to loosen that screw you don't even need to hold the nut.
After the initial release, it doesn't matter what you hold and what you turn, but you still have to apply torque because of the U mechanism on the nut (it's instead of Loctite, etc.). LINK to Partzilla
Font Screenshot Automotive tire Cable Gas

The closing/tightening torque is on the screw head, NOT on the nut. The reason: The Diameter of the nut is about twice as large as the diameter of the head of the torx, so the nut produces much more torque.

I'm guessing your mistake was when you tried to loosen the initial tightening by turning the nut, instead of turning the head of the screw. I'm also guessing that when you turned the head of the screw you used Allen and not Torx-T45 so the head of the screw rounded too.
 

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There's very little lateral load from sprocket on these bolts, so very little force on nuts. It only requires enough clamping to generate sufficient friction to transfer power across to spocket carrier. On bigger bikes, many uses smaller hollow 8mm bolts for this application. Similar to brake-rotor bolts in front. Which faces much, much higher loads.
You are right about the friction.
You are wrong about the importance of bolt strength for shear.

Because it is a safety system, the manufacturer also calculates the screws for shearing (in case they start to loosen, then in this case they must still hold the torque. When the screws have a diameter of let's, say 8 mm, then:
  • either the manufacturer adds additional screws,
  • or the manufacturer builds the screw with a pin that is thicker than the screw
Automotive tire Font Gas Screenshot Cylinder
 

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B.C-Rob You did a very good job(y)(y)(y), & thank you very much for sharing your job story and the photos (in the following link):
Cbr300r sprocket kit 14t/36t
The ratio in the CBR250R is 14/38T
Paying attention by switching to the 14/36T ratio there is a two things besides improving the opening accelerations:
  • The speedometer that translates the speed according to the engine rpm will now read you the speeds +5.5%.
  • The chain is now closer to the swing arm, which will increase the wear of the rubber (rubber part number 52170-KYJ-900 - link to Partzilla)
 

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(SNIP)
The closing/tightening torque is on the screw head, NOT on the nut. The reason: The Diameter of the nut is about twice as large as the diameter of the head of the torx, so the nut produces much more torque.
(SNIP)
Hmm...I understand your point, but -

I would expect to be able to put a lot more torque on the nut, using a standard socket, than on the Torx bolt. It's very easy to snap a Torx bit when using an impact, and it may be extremely difficult to loosen without.

In this case, I personally would always hold the Torx bolt and use an impact with a socket on the nut. It may require more torque to remove, but you would have a much lesser chance of stripping/damaging the fasteners by using a socket on the nut for removal than a Torx bit on the bolt head.

Danno?
 

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I would expect to be able to put a lot more torque on the nut,
YES BUT When the closing torque is determined by the screw head, it is a mistake to try to open a BIG nut that is currently loaded with a tightening torque beyond its capacity (its diameter creates a larger torque).
It's very easy to snap a Torx bit when using an impact
This will be true for many situations, impact is not a magic solution for all situations. I've already had to grind a stubborn screw head this way.
In this case, I personally would always hold the Torx bolt and use an impact with a socket on the nut. It may require more torque to remove,
YES BUT ...ended up with a round nut?
 

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In this case, I personally would always hold the Torx bolt and use an impact with a socket on the nut. It may require more torque to remove, but you would have a much lesser chance of stripping/damaging the fasteners by using a socket on the nut for removal than a Torx bit on the bolt head.
NOT GOOD
In the best case, if you don't hold the head of the torx screw, the head of the screw will slide and turn in place, then the nut won't open, but it won't be destroyed either.

Maybe the friction will be strong enough release the screw head? but that in condition that you don't try to grab the head of the screw.
The correct way is to open the screw head.
 

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There's way to do it so you never strip bolt-heads or nuts. You're more than welcome to keep on stripping bolt heads if you want. Much, much more successful to loosen nuts first. Don't even have to hold bolt-head because it won't spin until interface is loosened by spinning nut. THEN you can hold bolt-head and minimal torque is needed and no chance of stripping.
 

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You are right about the friction.
You are wrong about the importance of bolt strength for shear.

Because it is a safety system, the manufacturer also calculates the screws for shearing (in case they start to loosen, then in this case they must still hold the torque. When the screws have a diameter of let's, say 8 mm, then:
  • either the manufacturer adds additional screws,
  • or the manufacturer builds the screw with a pin that is thicker than the screw
View attachment 45654
Shear loads on bolts are exactly same regardless of bolt size. A 25bhp motor pulling on chain at WOT generates exact same shear forces on any bolt that holds sprocket to carrier regardless of that bolt's size.

On 250bhp bikes, they use 8mm bolts. When loaded, highest stress is on smallest diameter section of bolt, the 8mm. Larger shoulder is only to achieve precise centering of part on initial install. Looking at both sprocket and carrier, you'll find that shoulder of bolt only touches sprocket. Pocket in carrier is larger and shoulder never touches it. There are no contact fretting marks on pocket in carrier, showing no contact and no movement. Once sufficient tension is achieved correct friction, bolts DO NOT experience any shear forces, only tension from tightening torque. Friction transfers across interface and there's zero relative movement between sprocket to carrier.

Take your front-rotor bolts off, scratch a mark across rotor to hub and put back on and ride for a while doing maximum-braking. Then examine interface. You'll see there's zero rotational movement of rotor relative to wheel-hub. Friction is higher than forces rotor experiences and bolts are never loaded in shear (engineering no-no).

Read up on how bolted interfaces work here: Bolt Science Web Site
 

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Once sufficient tension is achieved correct friction, bolts DO NOT experience any shear forces,
YES & NO
When the screw is released (For any reason of tightening with too low torque, etc...then the screw does have to withstand shear forces.
It's a matter of additional assurance in the engineering design (In systems with a high level of safety).

Yes, there are other reasons for that pin. I mentioned the reason relevant to our topic.
Another example of the use that pin in engineering: In plastic cover, there the pin is often used as a spacers, etc.
 

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NOT GOOD
(SNIP)
The correct way is to open the screw head.
Not gonna work for this...

I'd never do it that way - it's just looking for trouble.

The nut isn't going to strip with a proper fitting socket, unlike a bolt with an Allen/socket head or Torx screw head.

It may be fine to install it that way, but not remove it.
 

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YES & NO
When the screw is released (For any reason of tightening with too low torque, etc...then the screw does have to withstand shear forces.
It's a matter of additional assurance in the engineering design (In systems with a high level of safety).
Shaft of bolt only experience torsion when bolt tightened and loosened.
 

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Not gonna work for this...

I'd never do it that way - it's just looking for trouble.

The nut isn't going to strip with a proper fitting socket, unlike a bolt with an Allen/socket head or Torx screw head.

It may be fine to install it that way, but not remove it.
Yep, and according to Einstein and Relativity, it doesn't matter if you spin bolt or nut to tighten or loosen, effect will be same. They will rotate same X-turns relative to each other and torque will increase or decrease same Y-amount either way. Nut with 6-side socket is way, way more secure and sure way to loosen without stripping.
 

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way more secure and sure way to loosen without stripping.
There is nothing that will destroy a nut or a bolt head faster than an impact drive.
Oh how fast it happens. Impact drive is very limited tool, and whoever uses it must be prepared for the other result, which is continued cutting on with disk, just like our friend B.C-Rob did anyway(y)(y)(y)
It is not always possible to use a disc (for example when the screw head is sunken), but our friend demonstrated an effective use of the disc and solved the problem very nicely(y)(y)(y)

And after all that when you have a pair of a torque nut with a normal screw head, the torque needed to tighten the nut is higher compared to the torque needed to tighten the screw head, when in both you will get the same tensile force needed for tighten. The easy way to release such a pair is to open the head of the screw (the nut holds itself).

Maybe Rob's problem was caused by someone before him that tightening the head of the bolt in the torque a mount that should have tightened the nut. Honda gives the tightening torque to the NUT (75Nm 55Lbf) and NOT the bolt.

P.S. And if I already mentioned "easy way", I would loosen the bolts while the wheel is still in place.
 

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The nut isn't going to strip with a proper fitting socket, unlike a bolt with an Allen/socket head or Torx screw head.
The screws that get stuck probably haven't heard of your interesting theory. Even if there is a special anti-slip socket, it is possible to destroy a screw that is properly stuck.
It may be fine to install it that way, but not remove it.
Honda gives the tightening torque to the NUT (75Nm 55Lbf) and NOT the bolt.
But to release a pair of nut and screw, like in this case, it is better to go to the head of the screw and not the nut.
 

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Shaft of bolt only experience torsion when bolt tightened and loosened.
NO
In our case, NOT when the screw is already loose (even when and the parts are still attached to each other), in this situation the tensile force is equal to zero, and the shear force is the force felt in the screw.
 

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@Tamir

Thanks for your feedback but you have made a few misleading mistakes.

1. The bolt is 100% hex and not at all a torx head. I have torx wrenches and have use them many times in past. This is hex. As you can clearly see.


2. The torque applied is determined by the length of the wrench I use, not by the size of the hex hole/nut used to loosen the combo. The reason the bolt wouldn't come off was due to the locking tabs on the nut, I was aware of this but it didn't help me undo them.

The nut/bolt combo was perfectly clean, no rust or grime. The heads on either end were not rounded. I put enough torque through the nut to round the nut, and the nut didn't budge. This shows the locking tabs on the nut were the issue.

For future reference, anyone else trying this job. If you can't remove the bolts easily I would recommend just grinding/drilling the heads off vs wasting time trying to undo them.
 

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The bolt is 100% hex and not at all a torx head.
OK. As I already wrote, you did a very good job.
For me, the dirt hides some of the screws, maybe I clean them later on and download pictures of them.
Maybe I also already have the non-original Torx. Looks like I have a mix of Allen and Torx, but need to clean to be sure.
Maybe a testament to the difficulty of the last owner that replaced the sprocket.
Maybe he also had to cut off the head of the screw with a disk😅🤣

I am guessing that the problem is related to over-tightening these screws, by mistake the screw head is tightened to 75Nm and this is a tightening torque of the nut and NOT of the screw head.
The torque applied is determined by the length of the wrench I use, not by the size of the hex hole/nut used to loosen the combo.
Yes, BUT there is the torque that goes to tightening, and the torque created by the friction in the opposite direction. The diameter of the screw head is significantly smaller than the diameter of the special nut, so the special nut produces more friction torque for the same perpendicular force. We tighten from the side of the nut, and open from the side of the screw head, because there the opening torque will be lower. But it is possible that the screw head was tightened much more than allowed (75NM), then when you try to open it the screw head is destroyed.
For future reference, anyone else trying this job. If you can't remove the bolts easily I would recommend just grinding/drilling the heads off vs wasting time trying to undo them.
And thanks for coordinating expectations, and thanks for the encouragement. To remove a screw head with a disk in this case is really not as bad as it sounds, and as you write, this is the easy and correct way to your problem.
 
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