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Old 02-25-2013, 11:21 AM   #749
because I can
Joined: Sep 2010
Location: San Francisco Bay area
Oddometer: 9,116
Originally Posted by Plaka View Post
The engineering of the joint is a particular torque applied to a particular bolt that is intended to distort and provide a locking action. The bolts are not re-used because they can only meet the specification once.

You can deny any bit of engineering on the machine that you want. You say you have had no problems. great, you have one data point. The people that engineered that joint have thousands of data points and more testing than you will ever do riding. personally I'm going to go with what they came up with. I know they've changed the joint and I also know they didn't do it for production economy reasons---they had a problem. it wasn't a big enough proplem to do a recall, but they did spec the newer bolts for service on the older machines. The torque specs have a tolerance. From the factory, some bolters fer at one end of the tolerance, some at the other. The variation tends to be sinusoidal. it may be that only fasteners at one extreme of the tolerance had problems. on solution is to tighten the tolerance. But this is costly. Another is to change the fastening system to be more reliable across the tolerance range. I suspect this is what they did. The fastener will distort enough throughout the tolerance range to give acceptable locking.

You can set up one bike and reuse your fasteners and have absolutely no problems. You can also buy one lottery ticket and win the lottery. it's a statistical game either way and you really don't know what the statistics are. BMW does know. If there is a problem they hear about it.

BTW, you mention you have seen a lot of drive shaft bolts come loose because they weren't tightened enough. Were you there when they were tightened? How do you know they weren't tightened enough? (aside from simply assuming it---ie, some seriously circular logic). What is inarguable is that you have seen loose drive shaft bolts. (I ain't gonna call you a liar). it could very well be that they were tightened just fine...but they were re-used. Do you really know the history that caused the problem?

You can say you are a professional mechanic but if you don't follow a spec on something like this you aren't one I would patronize. You might be re-using conrod bolts too. if I want an engineer I hire one. i expect a mechanic to be exactly that even though many (like many machinists) feel they need to play engineer for...I dunno what? Status? In my experience both machinists and mechanics often know things the engineers don't simply because a lot of engineers are clueless about either discipline. But it cuts both ways and when things go wrong it isn't because engineers are trying to be machinists or mechanics.

There are a number of critical fasteners on my bike I have Re-engineered. I changed the material to stainless. It has less strength than 8.8 and has a habit of galling so it usually gets antisieze. My brake caliper bolts are an example. These suckers come in and out every time I take a wheel off. I decrease the torque because of the lubrication and check them a lot. I'm taking the risk on myself. So far they have not loosened between checks. When tight they are in pure shear and a pair of them is plenty for the forces the brake pots can exert. So I don't worry---but they are right out in the breeze and easy to check.
For starters, the bolt washer WAS a problem but loctite OR new bolts isn't going to help that issue either.

How do I know that the bolts weren't tightened enough when they came loose. Because I have never seen one come loose when I knew it was tightened right. Deduction. Plus it's not just my experience I am relying on but a number of other professionals.

Any professional that plays by the book 100% of the time is not being professional. The book is a great source of info but it is far from perfect. BMW is not a religion. Even religious zealots pick and choose what parts of the bible they are going to follow. A good mechanical zealot SHOULD do the same thing out of any manual. That is unless he finds one written by god. Personally, I will replace those bolts any time someone insists. Sometimes the used bolts need replacing anyway for being damaged. Other than that, all it is going to do is increase their bill but BMW knows that!
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