Focus Fanatics - View Single Post - Head Gasket Leak
View Single Post
Old 09-15-2010, 02:37 PM   #9
bradshsi
Focus Enthusiast
 
bradshsi's Avatar
 
Join Date: Aug 2008
Fan#: 58770
Location: Upstate NY, NY
What I Drive: 2002 Sonic Blue Turbocharged SVT

Posts: 215
FF Reputation: 6 bradshsi Good Standing Member
Buy-Sell-Trade Rating: (4)
A few points:

Retorquing is required if some of the preload in the head/gasket stud assembly has been lost. The whole goal is to have the assembly under sufficient preload so that the gasket stays in contact with the block and head while in operation. If you have insufficient preload, you will get leakage.

There is no harm in checking the torque on your studs after reassembly and cycling the engine a few times. A new gasket will relax to some extent as will new studs. Both these things will result in a loss of preload (which will exhibit itself as a loss of torque). The amount the gasket relaxes will depend on the gasket design and how hard you run the car.

The type of lubricant used on the studs has no influence on whether you will need to retorque. The stud lubricant only influences the coefficient of friction between the threads which in turn determines how much of your torque is turned into preload.

For similar geometry (length, diameter) and material, there is no difference in the "holding" power of a stud vs a bolt. Each will have the same spring rate and yield characteristics. Each will require a similar torque to seat it since in both cases you need to torque against the thread friction and the surface contact between either the underside of the nut or the underside of the bolt.
__________________
Sona si latine loqueris
bradshsi is offline  
    Reply With Quote