MGN54 Posted October 10, 2007 Share Posted October 10, 2007 This is the first time I've removed the front wheel on my new to me RT and one of the pinch bolts is being pesky. Left one broke free and is loose enough to turn with my fingers. Right one was very tight! Managed to loosen it about a 1/4-1/2 turn (puffed a little dust as it was moving) maybe which was enough to free the axle but she doesn't want to turn. Im actually wondering at this point if that right one had a grip on the axle at all. Hex head is starting to want to round off. Went ahead and pulled the axle and shot the pinch bolt threads with some WD40 to see if it will loosen up. Taking the rim in tomorrow to get front wheel installed. Just don't want to get in a mess over that right pinch bolt...either breaking it off or striping the thread on the fork leg! Should I get a little PB Blaster to hit it with? I'm guessing the sucker's got some corrosion forming making it a bitch to move. Hope that I can tighten it back up enough to pinch the axle upon reinstall. Sure don't want to break it off!!! Any and all advice welcome! Thanks! Mark Link to comment
Steve W. Posted October 10, 2007 Share Posted October 10, 2007 HEAT is your friend!! Heat up the aluminum with a good heat gun or a small torch. While it's hot try gently turning the screw. Should loosen right up. Don't force it, it will break off or strip the head. Once it starts turning work it back and forth like 1/2 turn out 1/4 turn in. When you get it out chase the threads with a tap and get a new screw. Good Luck Steve Link to comment
tomk99r11 Posted October 10, 2007 Share Posted October 10, 2007 Think it's stripped? Best to torque those things. Link to comment
DrPaul Posted October 11, 2007 Share Posted October 11, 2007 Galding (or galling) occurs when steel bolts are threaded into aluminum or a softer metal. It can be a recipe for disaster! Gently and slowly remove the pinch bolt. Don't get in a hurry. Heating the fork end will help. Run a tap through the hole to clean up the threads and clear any debris. Inspect the pinch bolt threads. They will likely be OK but replace if bad. Coat the bolt threads with an anti-sieze paste upon reinstallation and torque to spec. You need to watch this bolt carefully for a few hundred miles making sure it stays put! Link to comment
MGN54 Posted October 12, 2007 Author Share Posted October 12, 2007 Thanks guys! I purchased a propane torch and heated it up pretty good. Let it cool and started working on it and with a little patience I got it out! There was a little aluminum in a couple of threads which had me worried. I took the bolt from the other side and ran it in. It reached a point that it was snug but it did go all the way through and snugged up. I took it back out and the threads were clean. Guessing that there is a little bit of thread in the fork that is buggered a bit. Should I chase the thread? I will definitely use some antiseize this time as I reassemble. I need to get a new bolt as the head of this one was just to the point of stripping. I didn't have a lot of time so hit the Home Depot and found a bolt but it was 12.9 instead of the 8.8. Any reason this one wouldn't work? If so, I'll go to the bolt and fastener store tomorrow and get a 8.8 bolt. Dealer did not have one...imagine that! Any other wise words? Thanks, Mark Link to comment
Boffin Posted October 12, 2007 Share Posted October 12, 2007 Thanks guys! I purchased a propane torch and heated it up pretty good. Let it cool and started working on it and with a little patience I got it out! There was a little aluminum in a couple of threads which had me worried. I took the bolt from the other side and ran it in. It reached a point that it was snug but it did go all the way through and snugged up. I took it back out and the threads were clean. Guessing that there is a little bit of thread in the fork that is buggered a bit. Should I chase the thread? I will definitely use some antiseize this time as I reassemble. I need to get a new bolt as the head of this one was just to the point of stripping. I didn't have a lot of time so hit the Home Depot and found a bolt but it was 12.9 instead of the 8.8. Any reason this one wouldn't work? If so, I'll go to the bolt and fastener store tomorrow and get a 8.8 bolt. Dealer did not have one...imagine that! Any other wise words? Thanks, Mark The 12.9 bolt is a high-tensile strength alloy steel bolt and should be fine provided anti-seize is used to prevent corrosion. I would use a thread chaser to clean up the threads. Do not use a tap for this as they can cut too much, weakening the thread. Bolt Markings Andy Link to comment
Art.. Posted October 12, 2007 Share Posted October 12, 2007 BMW torque spec for this bolt is a dry torque spec, meaning they expect the bolt to be installed without lubrication. I do not remember if these bolts are plated or not, I'd have to go look at my bike, but my guess is that they are plated, given their location. If you are applying anti seize, you should reduce the torque spec by about 25% to prevent the threads in the fork leg from stripping, because anti seize reduces the friction on the inclined plane, which increases the clamping force for a given torque (twisting force). If you give me the anti seize info (copper based, molybdenum disulfide, zinc), bolt size and thread pitch, I can calculate the actual torque reduction for you. The 12.9 bolt will work fine, as Boffin has said. Link to comment
MGN54 Posted October 12, 2007 Author Share Posted October 12, 2007 Thanks Boffin and Art! Looks like I will just use the 12.9 bolt but need to probably get a thread chaser. Will the bolt supply house have one? Art, the antiseize is Type 13 copper based. Thanks for taking the time to work up the torque for me. Mark Link to comment
Art.. Posted October 12, 2007 Share Posted October 12, 2007 Standard: 8mm 1.25 coarse Grate 8.8 - Yield 640 Mpa 75% of yield zinc plated (I'm guessing) Torque - 42 Nm Your Bolt: 8mm 1.25 Course Grade 12.9 Yield 1100 MPa 75% of yield Copper based anti-seize Torque - 31 Nm I was pretty close when I said 25% Link to comment
MGN54 Posted October 12, 2007 Author Share Posted October 12, 2007 Art, Spec for pinch bolt is 22Nm so should I go 75% of that? ie... 16.5. Mark Link to comment
Art.. Posted October 12, 2007 Share Posted October 12, 2007 Well, I removed the zinc plating from the calculation and came up with 25 Nm for the stock bolt, so we're close to your 22. Then I assumed we'll ignore the yield on the 12.9 bolt for this calculation. I added the copper anti-sieze and calculated 18.5 Nm. So........yes, use 16.5 for now, and replace that 12.9 bolt when you can get a new stock bolt. Why? Because the higher yield on the 12.9 bolt requires a greater torque to provide elastic clamping force. The aluminum mating part can't take that greater torque, the threads will strip. Therefore, you need to reduce the stiffness of the bolt to gain back the elasticity (preload) that was originally designed into the joint. Sidenote - I went back and calculated your 12.9 bolt at 16.5 Nm with anti-seize, and that bolt is at about 40% of yield. (normal joints are calculated at 75% of yield.) Although 40% is on the low side, we're splitting hairs and you will be fine with that bolt. The only reason I sweat about these bolts is that they are a key structural part of the motorcycle, and I don't like to take chances. Link to comment
MGN54 Posted October 12, 2007 Author Share Posted October 12, 2007 Ok, that is starting to make sense to me now. I'll use the 12.9 bolt for now. Have to order up some brake disc bobbins so I'll order a stock bolt as well and replace the 12.9 when the wheel has to come off again for that. Thanks for your time. Good news is, I learned something today! Thanks! Mark Link to comment
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