041

Hey all, recently just completed the 120k/12 year PDK and differential service on my 2012 991.1 C2S w/ 31k miles. In the process of replacing the PDK pan/filter I realized I was missing 1 of the 13 new aluminum screws in the kit I purchased. Since the old pan was already down and the fluid was drained, I continued with the job and reused 1 of the old original bolts that I had removed and torqued them in the correct sequence and the 2ft-lbs the service manual calls out. I believe these are aluminum bolts and should not be reused (are they considered torque to yield?). I have a new bolt on order, but is it worth replacing just the 1 old bolt and risk compromising the seal? A new pan and fluid is over 400 dollars and would prefer to avoid doing the service all over again. Any thoughts or experience with reusing the screw and/or replacing just the 1 while the pan is installed?

Also, the service manual mentions “Tighten M6 screws at ‘medium’ setting.” Anyone figure out what “medium” means?

Jack F

Medium is not difficult to figure out but you need to know what type of M6 screw you have.

SilverSFR

Here is a good reference for maxim torque setting (Nm) for different steel M bolt grades. I would be curious as to what percentage of maximum torque, medium torque is. Also do aluminum bolts have different grades and torque specs than steel bolts? The chart below is for steel bolts so if aluminum bolts have different grades with different torques the chart might not even apply.



One Newton meter/metre (Nm) = 0.7376 lbf.ft
To convert your Nm figure to lbf.ft, simply multiply it by 0.7376

041

Cool thanks for the responses/references. I think the aluminum bolts would have a different grade/strength than their steel counterparts. I saw in another thread that apparently the additional torque would be 90 degrees for an aluminum bolt:
https://rennlist.com/forums/cayenne-...l#post16490022
The thread was for a Cayenne, but what I gather is that aluminum bolts seem to require an additional torque past the initial torque rating. Not sure if that’s what the service manual refers to as “medium” torque after that initial rating.

Autobahnschreck

Porsche specifies to tighten these Al bolts with their special, quite expensive ($$$$) tool . It is electronically measuring the increase of torque with rotation angle ( mathematically speaking: the differential quotient of applied torque over rotation angle), and can be set to "low" , medium" and "high".
The setting dictates how close the final torque is to the yield limit of the material, or beyond.
This suggests that it is good practice not to use the bolts again. (Given the setting is "medium" some may consider this "German over-engineering", and a second use might be in order, if the Porsche tool is used).
The engineering wisdom behind the special tool is to more precisely relate the applied torque to the actual stress in the shaft of the bolt than you can achieve with a conventional tool, that just releases or "clicks" at a dialed-in torque (hopefully precisely).
In reality, much of the torque applied for tightening a bolt is to overcome the friction between the head and the part the head exercises pressure on, plus the friction within the thread. Both friction components vary considerably, depending on materials, their surface roughness, and, if any, the kind of lubrication applied.
Consequently, the actual stress applied to the bolt, and the more, how close it is to the yield limit, is not well defined, even if tightened with a precise torque value.

If you use a conventional tool with recommended ( by whom, for exactly what material ?) torque values on your PDK pan Al bolts, you are somewhere between the risk of a leaking oil pan, or an overstressed bolt, but you are not really sure, where. The more, as presumably the strength of the bolts supplied by Porsche is unknown.

And no, you may not use tables for torque to be applied on steel bolts for bolts made of Al alloys ( nor on bolts made of stainless steel).
Streng verboten !

RennListUser01

Just think of all those transmission and engine pans that were installed correctly, with either gasket or sealant or both, but not torqued at all ... figure millions a year? What percentage leaked?

And, then consider the implications of reuse of one fastener out of 13 ... even aluminum?

I would have continued as OP did, selected a nice looking screw from the used pile, and put it in with about the same torque as the new ones.

Jack F

I missed that they were aluminum bolts.

Here is a previous discussion about aluminum bolts.

https://rennlist.com/forums/cayenne-...al-torque.html

Aluminum bolt is going into what material? If it’s a harder material then if you over torque you will likely strip the bolt threads. If everything goes bad and head shears off, you now have a huge pickle to deal with.

Nashvegas

I think you did the best thing given the available options. (other than waiting for a new fastener to arrive... which is likely not feasible)

I would drive it, see if it leaks. If it doesn't leak, good to go.

041

Thanks for all the suggestions and assurance. I received the replacement bolt today and since I did not actually do the final rotational torque after doing the 2ft-lbs initial torque, I'm thinking I can still just replace the 1 bolt now without redoing the whole procedure. I can then do the rotational torque in the correct sequence called out in the service manual (I'm guessing around or under 90 degrees as they're the same bolts used in the Cayenne thread I linked before where they prescribe a degree measurement instead of using the medium setting on the expensive torque wrench). My concern with the old bolt was it snapping while driving and causing a catastrophic leak. While the risk is low since it's a static part, I've seen this happen on BMWs with aluminum water pump bolts when reused.

Maybe a lot of this is just paranoia at this point