Borrowed Time


5 replies to this topic
  • tjl1

Posted April 12, 2010 - 04:23 PM

#1

I'm having an issue with sprocket bolts on a WR450. A few weeks ago while riding I just happened to stop and take a look at my back sprocket. I had lost 2 bolts and the rest were loose. Luckily, I was with other people and they were able to retrieve a couple of bolts and nuts with the wrenches to get me back. I later removed all of the bolts and nuts, cleaned them and re-installed with lok-tite. This past weekend, again I happened to stop and check the back sprocket. This time I sheared off all but two. I limped back to camp and counted my blessings.
I've been pretty lucky so far but at some point my luck will run out. My plans are to purchase all brand new nuts and bolts, clean the hub and sprocket and torque everything as it should be. I'm concerned that the first time the bolts loosened, it 'opened' up the holes in the hub and this may be the cause of the shearing of the last bolts. If this is the case, is there a 'fix' without having to buy a new hub?

Thanks in advance!

  • WR_Dave

Posted April 12, 2010 - 04:29 PM

#2

Elongated holes will definetly be an issue. The only real proper repair is a new hub. You may get away with going to the next size bigger bolt and drilling the hub, but I would always be wondering. I had a friend have this happen a few years ago and it completely ruined everything when it came apart. (E-Bay here you come) One thing to keep in mind is to torque the nut and just hold the bolt with the allen wrench. Torquing from the tapered bolt side doesn't give an accurate torque due to the drag of the bolt surface area. All surfaces must be extra clean as well. Sorry for your luck. :thumbsup: WR Dave

  • Butta

Posted April 12, 2010 - 08:02 PM

#3

Try using washers, too....a buddy had a problem with a KTM losing sprocket bolts. He switched to Yamaha bolts/nuts/washers and never had another problem....we think the washers did the trick.

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  • tjl1

Posted April 13, 2010 - 07:57 AM

#4

Thanks for the info. I'll try going oversize hardened bolts with washers until I put a new hub on her. Hopefully taking it easy and constant checking will get me through a weekend or two.

  • GCannon

Posted April 13, 2010 - 07:58 AM

#5

Once the bolts start to stretch then it will continue. over torqueing is also a problem. New sprocket and bolts would be a good start but as mentioned earlier if the hub has damage to the holes then they will move around and you continue to have problems.

  • gsa102

Posted April 13, 2010 - 08:16 AM

#6

Make sure it is clean with no lube on anything, including the bolts!

Most bolting systems are designed to hold by clamping force making friction between the two parts rather than by resisting shearing forces. I would try the oversize bolts first and get proper torque on them. Use the torque spec. for the bigger bolts, as you shouldn't deform the other parts.




 
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