Head bolt head stud torque discrepancy

[Trucky McTruckface]

I am reinstalling the head on a 1.6 diesel that originally had the factory 11mm head bolts. I am using the ARP 204-4701 head studs that were recommended. The Bentley manual says that the final torque specification is 66 ft lbs of torque. The paper that came with the head studs says that the final torque is 80 ft lbs. I am unsure of what the proper torque is because I am not using the head bolts that the Bentley manual has in mind however I am also not using the ARP studs on the application that they were made for. What torque specification have people used? I am using the thread lubricant supplied with the studs top and bottom.

[Trucky McTruckface]

Has no one ever used these before?

[TylerDurden]

I have not. I even have a set and an 11mm 1.6 engine.

I've read (on another forum) that even with studs, the 11mm block is a crapshoot, to the extent that many folks will not even bother trying to work with a defective design. That said, you could go with the 80 and see if you get a leak... that's a PITA but still better than a cracked block. If a 12mm engine falls in your lap, run all your gear on that.

[Trucky McTruckface]

I know an over torqued gasket can also give problems. I just wish I knew more of the rationale between the 14 ft lbs torque difference.

[TylerDurden]

The torque difference is simple: the thread pitch of the nuts for the studs is different than the pitch of the threads that go into the block.

A shallower pitch will create more clamping force for the same torque.

[Trucky McTruckface]

I suppose by that logic the studs would produce more clamping force per specified torque and their torque recommendation should be lower than the 66 ft/lbs recommended for the bolts. Again, doesn't really make a lot sense, but I went to 80 ft/lbs as recommended by ARP. May god have mercy on my block.

[greg lousy]

I used the same studs on my caddy and went with the higher torque specs that came with the studs. got a good seal and no problems. At the time, i think I went this way because I had a thicker, three notch gasket and a less than perfect mating surface on the block.
another possible account of the difference is that with the studs, you're only getting the resistance of the top nut going around the threads, as opposed to turning a bolt through the larger area of threads at the bottom of the block. just spit balling here.

[Fatmobile]

Glad to hear you did the headstud upgrade. I don't put a head on an 11mm block without using studs.
80 should work just great, I think I went to 90 on the ones I have done.