99 boxster clutch

[JFP in PA]

Originally Posted by Boxstard

Again the point is if the spec was designed for dry or lubed condition. Dry spec can be developed to statistically assure the min clamp force for the application and still under material yield. It is risky to torque with lube when the spec really meant for dry...

I’m sure ARP as a fastener company advocates lube that reduces variations and achieves clamp force intended as consistent as possible for their optimal design without overengineering.

It was just not clear to me if Porsche spec. was based on dry or lubed, as I have not seen factory document specifying to lube.

And again, the point of any torque spec is getting the correct clamping force between two parts, which is rarely achieved with out proper lubrication of the fastener being torqued.

[Boxstard]

Originally Posted by JFP in PA

And again, the point of any torque spec is getting the correct clamping force between two parts, which is rarely achieved with out proper lubrication of the fastener being torqued.

I know you are the expert

Just saying that proper clamp force (or practically anything) has some acceptable tolerance range, and dry spec can be (should be) developed based on variations from components, friction/ stick-slip, etc. and yet to assure the clamp force in the proper range, instead of hitting the exact number... I do not have a fancy torque wrench with precise load-cell either but assuming some gage error is in the factory equation of the spec.

I do not have factory service manual but the owners manual and Bentley I have handy do not indicate to lube....

And just for reference... 718 manual says NOT to grease (lube) those bolts... I know, different car/ design but.

[JFP in PA]

Originally Posted by Boxstard

I know you are the expert

Just saying that proper clamp force (or practically anything) has some acceptable tolerance range, and dry spec can be (should be) developed based on variations from components, friction/ stick-slip, etc. and yet to assure the clamp force in the proper range, instead of hitting the exact number... I do not have a fancy torque wrench with precise load-cell either but assuming some gage error is in the factory equation of the spec.

I do not have factory service manual but the owners manual and Bentley I have handy do not indicate to lube....

And just for reference... 718 manual says NOT to grease (lube) those bolts... I know, different car/ design but.

Attachment 21762

I would agree against using grease on the lug bolts for multiple reasons, but we would still use anti seize, which also functions as a lubricant during assembly.

[JFP in PA]

Originally Posted by Boxstard

Just saying that proper clamp force (or practically anything) has some acceptable tolerance range, and dry spec can be (should be) developed based on variations from components, friction/ stick-slip, etc. and yet to assure the clamp force in the proper range, instead of hitting the exact number... I do not have a fancy torque wrench with precise load-cell either but assuming some gage error is in the factory equation of the spec.

Attachment 21762

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...………….

[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.

[JFP in PA]

Originally Posted by Boxstard

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?

No, I do not agree that there is a risk of over torqueing a given fastener because it is lubricated. In over four decades of lubricating fasteners prior to torqueing, I cannot say that I have ever seen one fail as the result. I would agree that there is a significant risk of under torqueing a fastener because it was assembled dry, causing the drag of the dry thread surfaces to be interpreted as the correct torque value.

And yes, we lubricate every torqued fastener. And in all the years I have been doing this, I have NEVER encountered a spec that specified dry rather than lubricated torque ( or the other way around) by any manufacturer. They simply give a torque spec or range, expecting the tech to be sure all the treads are clean and move freely in order to achieve the desired clamping force.

[Boxstard]

Originally Posted by JFP in PA

No, I do not agree that there is a risk of over torqueing a given fastener because it is lubricated. In over four decades of lubricating fasteners prior to torqueing, I cannot say that I have ever seen one fail as the result. I would agree that there is a significant risk of under torqueing a fastener because it was assembled dry, causing the drag of the dry thread surfaces to be interpreted as the correct torque value.

And yes, we lubricate every torqued fastener. And in all the years I have been doing this, I have NEVER encountered a spec that specified dry rather than lubricated torque ( or the other way around) by any manufacturer. They simply give a torque spec or range, expecting the tech to be sure all the treads are clean and move freely in order to achieve the desired clamping force.

Thanks or following through and sharing decades of experience.

My mindset is (was) that the torque spec is based on dry unless the manual/ procedure specifically calls for lubing the fastner (like locktite or threat sealer that may be called out for certain bolts), not mentioning some common sense that threads need to be clean and in good shape without causing extra friction and resulting in under-torque.

Obviously you think otherwise, more like lube is given unless OEM explicitly says not to lube for the given torque spec.

I just showed one example below, 718 manual specifying 'no grease' to wheel bolts to tighten to the specific torque, and I'm not splitting hair between grease and anti-seize here; they are lubricant.

You may be right that you have less risk to torque to the spec. with lube, if it is not clear that the torque spec is based on dry or lube. As mentioned before, I'm sure that components are designed with enough safety margin to take extra load, and probably it takes tons to actually tighten a faster to cause stress over material yield without feeling something is going wrong, starting to strip the bolt head or thread...

I'm not a professional mechanic, just an enthusiast with engineering degree and wrenching personal cars for 3 decades... not a P car (yet) but rebuilt 2003 Saab 9-5 engine from a bare block too that has 80K miles and counting, and never had issues of fasteners came lose so I can't be that bad