clutch and tranny bolts

[lunchbox]

Hi all,
In doing research a long time ago, (a year plus) for how-to on a clutch plate I remember reading somewhere the clutch bolts for the rear pressure plate were a one time use item. Is this correct or can they be reused? Also remember somewhere it being said that the tranny bolts were also one time use.

Neither bolts appear to have any specialness to them in the way they are made so it would seem they are reusable.

Thanks

[Rick G]

The clutch bolts are a one time only or so BMW says but I have reused them without failure. I have had ti drill the head of them quite often as the socket head is very shallow and a heap of care is needed to get them out. Clean the inside if the head before you attempt to undo them.
The Trans bolts are just normal 8.8 metric bolts and can be reused. I apply an antisieze compound to all the bolts that go into aluminum to prevent electrolisis and siezing next time.
Make sure you mark the plates so they can be reinstalled correctly for the ballance.

[frankenduck]

The clutch bolts and main clutch nut are all supposedly one-use items.  Like Rick G, I've re-used them on numerous motobricks without issue.

One trick for making the Allen bolts a bit easier to remove without stripping them is to heat them up with a torch (I use a small butane torch) to help break them free with out stripping the head.

Agreed that there's nothing special about the bolts that hold the tranny to the bellhousing.

[kennybobby]

You guys probably already know all this stuff, but most bolts used in life-critical components of machinery are single-use due to both technical and legal concerns. 

All bolts are designed to stretch when they are torqued to provide the clamping force necessary to hold stuff together.  When you re-torque a used bolt then you stretch it again past where it went before, which necks down the diameter even more and reduces the tension load margin of the joint.  Exceed the margin limits and it will snap and fail.

When you buy (or perform Factory Authorized Service Work on) a used bike, then you don't really know the history of the life-critical fasteners such as on brake rotors or clutch plates--whether they have been re-used multiple times, or possibly over-torqued by a previous owners, etc.  They are an uncertain item with respect to being able to provide the designed clamping force with adequate margin.

The design engineers have the liability and they signed off on the design based upon the calculated loads and margins using a specific fastener.  But the OEM and their dealer service shops could not survive a wrongful-death lawsuit due the failure of a re-used fastener, and so the cheapest solution for them is to just specify and use single-use new ones every time. 

As a DIY owner it is up to you to decide:  how lucky do you feel versus the cost of a few bolts versus the cost of a catastrophic failure?   

Riding motorsickles is all about risk management, and wrenchin' is part of it...

[frankenduck]

I don't consider it being "lucky" at all.  That clutch assembly is considerably overbuilt.  In fact, the very same clutch assembly was used on the 130hp K1200RS that generates 10-11% more torque than a K1100 and roughly 30% more torque than a K100.  Then throw in the fact that even the K1200RS has a factor of safety built in and I'd say the chances of having a failure are somewhere between zero and none.

Not to mention that the size of those bolts is a standard size so they're most likely sized up from what would be theoretically required which means the factor of safety is most likely somewhat higher than would be required if they'd made a custom diameter bolt.

In order for those bolts to fail you'd need all six bolts and all three alignment pins to be under enough shear stress to all fail simultaneously.  And, in the event that that did happen, all that would occur is that you'd lose power to the final drive.

I'm much more concerned about and think there's much more risk associated with a drive shaft U-joint failure on the four valve bikes as that can (and has for some riders) cause the rear end to lock up suddenly.  I also think the braking system getting old (caliper pistons freezing or brake lines leaking/getting clogged) poses a much greater safety risk than re-using clutch bolts.

BTW:  My undergrad degree is in engineering where I spent quite a lot of time studying the properties of metals (stress, strain, shear, fatigue, deformation, failure, blah, blah, blah....) and how things are designed.

[wmax351]

BTW:  My undergrad degree is in engineering where I spent quite a lot of time studying the properties of metals (stress, strain, shear, fatigue, deformation, failure, blah, blah, blah....) and how things are designed.

I had a feeling that you had some engineering background. Where from?

[frankenduck]

I had a feeling that you had some engineering background. Where from?

University of Washington - Civil Engineering.  I had to take lots of materials classes as a prereq for structural engineering classes.

[lunchbox]

Thanks for the input, went for the re-use.