Cylinder head studs
11-25-2020, 01:16 PM
#1
Track Day
Thread Starter
Cylinder head studs
Greetings folks,
I had a post a few weeks ago about my 911 SC project. Essentially I am back dating the exhaust and re-sealing, cleaning up the engine and doing some maintenance odds and ends.
My cylinder head studs are all fine, and tight. However, it look's like the heads have been off at one time (car has approximately 105K on it), and the exhaust side studs appear to have a different appearance on the surface that you can see on the end of the stud with the nut in place, as compared to the intake side studs. I have not yet taken the nuts off, but I think the exhaust studs have been replaced at some time.
I plan on re-torqueing the right bank studs as I have a small oil leak on cylinder #6 were the cylinder meets the case.
My question is: if the studs have been replaced, what are the thoughts on what type were used. I am asking to determine what my retorqueing procedure should be, and what the torque spec should be. I believe the manual states 15 lbs./ft. then and additional 1/4 turn for the OEM studs. I have seen other procedures that describe tightening instead in three incremental steps to 24 lbs./ft, , and others in two equal steps to 38 lbs./ft.
As you can tell, I am new to this subject so any advice will be appreciated.
Marc
I had a post a few weeks ago about my 911 SC project. Essentially I am back dating the exhaust and re-sealing, cleaning up the engine and doing some maintenance odds and ends.
My cylinder head studs are all fine, and tight. However, it look's like the heads have been off at one time (car has approximately 105K on it), and the exhaust side studs appear to have a different appearance on the surface that you can see on the end of the stud with the nut in place, as compared to the intake side studs. I have not yet taken the nuts off, but I think the exhaust studs have been replaced at some time.
I plan on re-torqueing the right bank studs as I have a small oil leak on cylinder #6 were the cylinder meets the case.
My question is: if the studs have been replaced, what are the thoughts on what type were used. I am asking to determine what my retorqueing procedure should be, and what the torque spec should be. I believe the manual states 15 lbs./ft. then and additional 1/4 turn for the OEM studs. I have seen other procedures that describe tightening instead in three incremental steps to 24 lbs./ft, , and others in two equal steps to 38 lbs./ft.
As you can tell, I am new to this subject so any advice will be appreciated.
Marc
11-25-2020, 06:01 PM
#2
RL Community Team
Rennlist Member
Rennlist Member
I am pretty certain the lower head studs in the SC are Dilavar (special alloy) and the upper studs are a more conventional steel (please anyone who knows for certain chime in).
Dilavar studs do look different, so it is quite possible you have original studs (which given your relatively low mileage would fit...)
If you are going to re-torque, ideally you would KNOW what studs you have and follow those directions. Failing that, I suppose I would research the likely possibilities and select the most conservative torques. When I rebuilt my motor, I used the Henry Schmidt (Supertec) studs, which have a different pitch at the head end, so it really can be a much different situation.
FWIW, for my car (1985 3.2 Carrera) the FACTORY instruction was to torque the studs in two stages: Stage one to 15 Nm and stage two to 90 degrees, plus or minus 2 degrees. When I did my motor, I followed the instructions for the Supertec studs, which I don't remember off the top of my head. I am not sure if the 3.0 SC would have the same spec, I think it would, but I don't know. I only have the Carrera factory manual.
I know that is not a complete answer, but hopefully it is some information you can build on...
Dilavar studs do look different, so it is quite possible you have original studs (which given your relatively low mileage would fit...)
If you are going to re-torque, ideally you would KNOW what studs you have and follow those directions. Failing that, I suppose I would research the likely possibilities and select the most conservative torques. When I rebuilt my motor, I used the Henry Schmidt (Supertec) studs, which have a different pitch at the head end, so it really can be a much different situation.
FWIW, for my car (1985 3.2 Carrera) the FACTORY instruction was to torque the studs in two stages: Stage one to 15 Nm and stage two to 90 degrees, plus or minus 2 degrees. When I did my motor, I followed the instructions for the Supertec studs, which I don't remember off the top of my head. I am not sure if the 3.0 SC would have the same spec, I think it would, but I don't know. I only have the Carrera factory manual.
I know that is not a complete answer, but hopefully it is some information you can build on...
11-26-2020, 09:35 AM
#3
Team Owner
as noted above dilivar and steel ...
My advice.. head studs do not cause oil leaks, trying to torque them will not resolve your issue and possibly cause much more catastrophic issues.
My advice.. head studs do not cause oil leaks, trying to torque them will not resolve your issue and possibly cause much more catastrophic issues.