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Broken Hub (photos attached)

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Hello,

I was at the track and I saw a Honda rider shatter his hub. He was riding an '11 450R. He simply landed from step up and then I saw his rear wheel lock up. He said that he just tightened the bolts on the sprocket and such before he came out to the track, but they come loose really easily. This also happened on his 250R.

Is this because Honda has a weak hub? Or is this the cause of bolts coming lose, so maybe a type of locking bolt be used to prevent this?

The rear wheel locking up at the speed he was going would have probably taken me out.

Thanks

Josh

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Probably loose bolts, had this happen on my Yz once. Never could get them to stay tight. Bolts losen and fall out, sprocket comes out of alignment causing the chain to come part way off and get caught in the chain guide locking up the rear wheel which will give the hub/sprocket a twisting effect from the engine trying to turn the sprocket even after it gets slammed to a stop... alot of stress all at one time rips the rest of the connected bolts out. Mine wasnt damaged quite that bad but I was riding on flat ground during a break in so I wasnt hauling. Ended up going with aftermarket bolts with lock nuts on the back (I also used some mid strength loc-tight for additional strength. I doubt Hondas hubs were the cause of this.

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I am going to "guess" on this one ...

But I imagine your friend is REUSING the OLD sprocket bolts when installing a new sprocket.

Its always a good idea to buy new bolts when swapping sprockets. For the few $$$ it will cost you, the savings are well worth it. New sprocket nuts have a metal tab that locks the nut into place ... and are not meant to be re-used. :cheers: Put a bit of loctite on the threads for added good measure.

I have never seen this happen to anybody except those re-using old bolts.

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I am going to "guess" on this one ...

But I imagine your friend is REUSING the OLD sprocket bolts when installing a new sprocket.

Its always a good idea to buy new bolts when swapping sprockets. For the few $$$ it will cost you, the savings are well worth it. New sprocket nuts have a metal tab that locks the nut into place ... and are not meant to be re-used. :cheers: Put a bit of loctite on the threads for added good measure.

I have never seen this happen to anybody except those re-using old bolts.

Never even considered that until you just said that but I was re using the bolts when it happened to mine:banghead:

Thanks for that tip!

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That failure is self inflicted. When you allow the sprocket bolts to get loose just one time, it will ovalize the holes in the hub and ruin it. The sprocket bolts will never stay tight again.

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notice the missing sprocket bolt in the picture. Loose bolts and no locktit there.

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I am going to "guess" on this one ...

But I imagine your friend is REUSING the OLD sprocket bolts when installing a new sprocket.

Its always a good idea to buy new bolts when swapping sprockets. For the few $$$ it will cost you, the savings are well worth it. New sprocket nuts have a metal tab that locks the nut into place ... and are not meant to be re-used. :cheers: Put a bit of loctite on the threads for added good measure.

I have never seen this happen to anybody except those re-using old bolts.

over.. kill..

see above posts. I mean seriously, the same rider had it happen to TWO bikes, he owns. I have never had it happen to one honda dirt bike and presently own 2, and just got rid of my ol' 98cr250.

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over.. kill..

see above posts. I mean seriously, the same rider had it happen to TWO bikes, he owns. I have never had it happen to one honda dirt bike and presently own 2, and just got rid of my ol' 98cr250.

Agree somewhat ... buy spending $10 for cheap insurance is not overkill to me :cheers:

Your right though ... one bike .. maybe ... two bikes ... houston we have a problem :p

New bolts, loctite and proper torque ... about the same odds of this scenario above happening as me winning the lottery next week.:ride:

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Dude,your chain was too tite! :p

Winning~ :ride:

Thats where my money would lay. .

Id also guess that he's one of those guys that tried to tighten the bolts using the hex head in the bolt and holding the nut, instead of the other way around.

You'll never get proper torque on the sprocket bolt trying to tighten it into the counter sunk hole in the sprocket. Too much working against you. The taper and the surface area of the bolt head not to mention the length of the bolt through the sprocket all sucking up any perceived torque you put on the bolt head. Probably only half of what it actually needs. Then over tighten the new chain "because it'll stretch anyway" and thats what you get. :cheers:

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I see this at the track a lot. It's always initially caused by under-torquing the bolts, allowing them to get loose, then ovalizing the holes in the hub. Once the holes are ovalized, the bolts will never stay tight and eventually the bolts fall out and the hub goes BOOM. If you continue to use a hub that has been run with a loose sprocket, this will be the end result.

It doesn't have anything to do with over-tightening the chain, which is nearly impossible to do with the CRF because the chain rollers are positioned such that the chain never gets tighter as the swingarm moves through the stroke.

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It doesn't have anything to do with over-tightening the chain, which is nearly impossible to do with the CRF because the chain rollers are positioned such that the chain never gets tighter as the swingarm moves through the stroke.

Can you expound on this, Cam?

The reason I ask is my new chain is pretty tight, with the axle blocks all the way forward. I only have about 1/2" of play, but I guess I shouldn't be concerned based on the info you have.

Thanks!

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Can you expound on this, Cam?

The reason I ask is my new chain is pretty tight, with the axle blocks all the way forward. I only have about 1/2" of play, but I guess I shouldn't be concerned based on the info you have.

Thanks!

Sounds like your new chain is a link too short. I wouldn't use less than 1" of chain slack because when the sprockets are packed with mud, it reduces slack.

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Okay, thanks. There's always something with these toys of ours, isn't there?

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I see this at the track a lot. It's always initially caused by under-torquing the bolts, allowing them to get loose, then ovalizing the holes in the hub. Once the holes are ovalized, the bolts will never stay tight and eventually the bolts fall out and the hub goes BOOM. If you continue to use a hub that has been run with a loose sprocket, this will be the end result.

It doesn't have anything to do with over-tightening the chain, which is nearly impossible to do with the CRF because the chain rollers are positioned such that the chain never gets tighter as the swingarm moves through the stroke.

Unless your swingarm pivots on the same plane as the front sprocket the chain goes through a cycle of tighter and looser. The rollers merely help control this effect and keep the chain from rubbing things it should not touch. Thinking your chain tension does not change is a very wrong assumption.

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Unless your swingarm pivots on the same plane as the front sprocket the chain goes through a cycle of tighter and looser. The rollers merely help control this effect and keep the chain from rubbing things it should not touch. Thinking your chain tension does not change is a very wrong assumption.

Take your shock off and check the chain tension as it moves through the stroke. Honda's placement of the rollers is such that there is almost no tightening of the chain when the countershaft, swingarm pivot and rear axle are aligned.

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I agree with the "Chain to Tite" theory. I had a friend that was riding a YZF and he mentioned that he was always breaking the rear spocket bolts. So I was helping tighten the new set of bolts when I noticed that his chain was super tight when he compressed the supension.

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