Clutch wear calculation on a (pre-OTO) 612...what is the correct clutch disk thickness?

Hello Gents. I have had some trouble finding the correct answer on this and was hoping somebody here might be able to help. I'm familiar with the formula "Clutch closed position" minus "clutch closed position from new" divided by "clutch thickness" multiplied by 100...and so on... but I have not been able to find a good reference for the value to use as "clutch thickness" for my 2006 pre-OTO 612. I have measured a brand new clutch disk to be ~8.5mm, but it would seem odd to use that number in the clutch wear calculation since you cannot physically wear the clutch to "zero" thickness (you could never reach a "100% worn" condition). But I might not fully understand the topic. Please help if you can. Thank you.

 

Thank you for that info, Taz. I have never seen a reference for a "loaded" thickness of a clutch disk. Does that indicate that the friction material is compressible and that overall clutch disk thickness will change (reduced from 8.35mm to 7.7mm) when the pressure plate is closed? Which number would be correct to use as "clutch thickness" in the standard clutch wear formula?

Is there a specified thickness tolerance for the clutch disk? If I measured a used clutch disk with a micrometer, what would the minimum thickness be before it is no longer serviceable?

Ultimately, I would like to gauge clutch disk wear by comparing "clutch closed position from new" with the auto-calculated "clutch closed position". That is to say...estimated clutch disk thickness via reference to thrust bearing travel. I'm not so much interested in a "% worn", I'd prefer an actual measurement. Is that even possible? I realize that the diaphragm spring has a certain lever-arm gearing value (I've seen a post here that estimated 4:1) and that thrust bearing travel measurement does not directly correlate to pressure plate movement. Thanks for entertaining these odd questions.

 

Good point. I have inspected my clutch disk through the inspection ports, and have viewed the t/o bearing position with my boroscope and everything looks to be in great shape. No problems there. But the whole F1 system operation and clutch wear question seems to be a mystery to a lot of owners, and it would be nice to have some hard data to work with. As you said, the "wear percentage" numbers can be all over the map. I would think a hard number such as "when (self-calibrated) clutch closed position reaches "x", then your clutch disk has reached its physical wear limit." That would seem useful to owners. Of course, this is a moot point if the "clutch closed position from new" number has been incorrectly set or purposely manipulated.

 

I forgot to add: I feel like I understand the theory of operation very well. I have Aldous and others to thank for that. But what I'm missing is an official number to use for clutch thickness when running the clutch wear equation. Those numbers seem available for the 360 (8.5mm), 430 (5.6mm) and Maserati Cambiocorsa (5.6mm, as published in the official Maserati training manual). But I have not been able to find reference to the correct number for the 612. Or for the 575 for that matter. So is it 8.35mm, 7.7mm,...or something else entirely? Does anybody here know? Thank you.

 

That is really great info. Thank you, Mark, for taking the time to respond.