Rod Bolt Torque-new vs old specs

[Larry535]

Hi all, I am a newbie 911 engine rebuilder. I am rebuilding a '81 3.0 SC engine. I'm using Waynes rebuild book as my guide. My question concerns the torque value for the standard rod bolts. I replaced all rod bolts with new ones, followed the instructions in Waynes book for torquing ( init 20 NM, then 90 degrees more) and have them all properly torqued to this spec.
While researching other 911 info on the web, I found a porsche bulletin that states that the newer rod bolts with the 12.9 stamped in the heads have a different torque value of 15 Nm then 90 degrees. The replacement bolts I purchased are stamped with the 12.9 on the head. Does this mean that I am over torqued by 5 Nm?, Is that acceptable ?, Do I need to replace all my bolts?
Thanks for any help on this matter

[chris_seven]

The idea of using the angle method with a Stretch bolt is to reduce the torque to preload variation.

The angle tightening method for con rod bolts wasn't introduced until the 84/89 Workshop manual and until then the standard figures were 50/55Nm, so a 5Nm variation shouldn't be an issue.

If it is a stretch bolt when it yields it will not increase load in a linear manner with angle and this helps to control the preload.

If the bolt is marked 12.9 it is surely an ISO Grade 12.9 as for this to have any other meaning would be too confusing.

I am surprised that a Grade 12.9 bolt would be used as a stretch bolt as bolts of this grade wouldn't normally yield until a preload equivalent to around 100Nm.

The nominal maximum torque that you can apply to an M10 Grade 12.9 fastener would typically be 79Nm so even at 55Nm you would be well within the safe limit for an elastic bolt.

I would be interested to know where the statement about using 15Nm and 90 degrees is published as I have looked in the 84/89 manual and can't find any reference.

I wouldn't worry too much as I would be reasonably confident you will still be well within acceptable variation.

[Larry535]

Thank you for your response. It is much appreciated. I found the spec's in Porsche Technical Bulletin 9006 dated Feb. 16, 1990. If you google that bulletin you can find the PDF of it on a few different sites.
I'm surprised that there isn't much info out there about it. There was no warning (or any) documentation about the change in torque spec when I ordered the new bolts. I assume they must consider them interchangeable with the current specs as called out in Wayne's book.