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eckstine918

2010 yz450f wheel issue

7 posts in this topic

Came back from a moto and when I swapped the rear wheel I noticed the sprocket bolts came loose. All of them about the same amount. Not a lot just enough to make the sprocket loose. The holes are now slightly egged when I play with a bolt in them. I compared it to my known good wheel and they are sloppy also. About half what the ones with the loose sprocket are. My thought is this hub is trash. Don't want to risk it coming loose again. Opinions? Is the stock hub just not strong enough for a mod engine?

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If you ever change your sprocket on the rear you have to use brand new bolts with the brand new sprocket, and lock tite red thread lock.

Then you need to check the bolts every time you check the chain.

If you don't do both, you will end up with loose sprocket bolts eventually, and even worse, a trashed hub like you have now.

It's all about maintenance.

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You can reuse the hub. The bolts locate the sprocket by using the taper of the head, not the bolt hole, so a slight amount of wear in the hole is not a problem. At this stage you should use new bolts as the old ones may have stretched.

Sprocket bolts can be safely reused if you know they have only ever been torqued to specs in the past and if they have not come loose. If in doubt, use new ones. Always use red loctite and more importantly a good torque wrench. Dont just lean on them to check they are tight - you may overtorque them.

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The bolts locate the sprocket by using the taper of the head, not the bolt hole,

This is incorrect. The bolts are located in the sprocket by their heads, but in the hub, they are located by the bolt holes in the hub. If these become elongated, the hub may allow the sprocket to shift back and forth enough to be a problem.

Go and buy 3 1/4" roll pins. Mount the sprocket, rotate it as far forward as possible, and tighten it. Now drill into the sprocket near 3 bolt holes so that the hole passes through the sprocket and the hub at a good meaty part of the mounting tab. This hole should fit the roll pin tightly enough that it must be driven into place. You will want to leave one sprocket on the wheel for most of the time, rather than change them constantly, or you'll need to precisely drill each one to match.

If you have bigger money to spend, have a machinist bore the holes out, then make and press in steel sleeves in the 6 holes to bring them back to standard size.

The bolts loosened because they were not properly tightened, simple as that. A common mistake is to try to hold the nut and tighten the bolt. The friction from the tapered heads interferes with this, and will give you a false reading if using a torque wrench. Instead, reverse that, and hold the bolt while tightening the nut.

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I like roll pin idea! I was thinking the second option of boring and putting in a sleeve but was wondereing if it would actually weaken to point where it could break (assuming using collar that is ideal and not overkill in thickness or dia). Luckily I have never experienced this problem personally but have witnessed on some friends bikes. They bought used hubs

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Bolts were new. This was actually a spare wheel that I use for a different tire compound. The bolts were new when I put the sprocket on. It has been on there for almost a year. maybe 20ish hours on it before it came loose. I don't change my gearing so it is not like I was reusing them over and over. I did torque the nut and not the bolts

I may try to repair it but for know I will use my other wheel and may just get aftermarket wheels. Thanks for the input.

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Anyone dealing with this kind of problem should also take a good look at the backside of the sprocket where it faces against the hub flange. The mating face is likely to be "cratered" some, which will encourage them to loosen again, and will damage the flatness of the hub flange, if it hasn't already.

The clamping force provided by the tensile load of the bolts is supposed to hold the sprocket, not the integrity of the bolt against shear. A non-flat surface here will be a problem.

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