[Boxstard]

Originally Posted by JFP in PA

Problem with this tolerance range idea is what kind of range is actually acceptable vs. what range is obtained dry vs lubricated. The measured clamping force in the study showed wildly swinging numbers on dry fasteners, way beyond the observed range of those obtained with lubricated fasteners torqued to the minimum and maximum torque spec range values.

Another facet we have not touched upon is bolt stretching; Porsche uses many single use torque to yield fasteners, and particularly with the clutch and flywheel. None of these fasteners should ever be reused because of the stretch imparted during installation. The flywheel bolts are first torqued to a rather low setting, then stretched by cranking them some additional degrees. As a practical matter, if you have ever done one of these with and without lubricant, you would quickly realize that the dry fasteners are incredibly hard to move to their final position. I have actually watched my techs literally hanging, feet off the floor, on a 40 inch breaker bar trying to achieve the final loading angle, and not getting there on non lubricated bolts. Yet the same tech with the same tool on lubricated flywheel bolts can quickly crank them into their final position without all the fuss and excess force. So I ask you: Which one do you think is installed to the correct bolt stretch, remembering that unlike connecting rod bolts, there is no practical way to measure flywheel bolt actual stretch value? And speaking of rod bolt stretch, running them dry and trying to use the torque spec range as upper and lower limits, it is nearly impossible to get them to the correct measured length, while lubricated bolts will fall into the correct stretch within the torques spec range. Lubrication matters more than you might think...………….

I’m not debating positive effect on lube on accurate torque etc. And my simple answer? If OEM specifies certain torque value based on dry, then I’ll do so without lube and won’t lose sleep over it. If the spec calls for lube then that’s how I do it and again no worries...

I hope you agree potential risk with lube and torque down to the spec. originally meant for dry where clamp force may get close to or exceed yield strength of materials. Do you lube every situation calling for certain torque spec, regardless? Or if the spec is meant for dry you calculate new lubed spec based on frictions etc. (rule of thumb may be 20% less?) to avoid over stressing while improving accuracy/ consistency with lube? I was just making a point not to blindly lube bolts and torque to the spec. without knowing if the spec is actually meant for lubed condition.

With all said, I think OP (or someone here) should confirm if the spec. for flywheel bolts are based on lubed or dry. I checked Bentley and Dempsey’s 101 projects book but did not see lube as procedure.