schaef_12

Just doing some retorques on my headstuds after installing them, and according to arp's instructions it says to loosen then tighten the nuts. Why not just retorque the stud withouth loosening it?

CamperAndy

Part of the (may not be the whole) answer is break away torque. Once they start to set the break away torque may be higher then the target torque so you may not actually get the correct re torque. So to over come this issue you release the break away torque by loosening the studs and starting over.

dieselman2300

Its to seat the gasket, and to also stretch the studs.
I wouldnt do the retorques like ARP says.
This is the way I was told by a big diesel engine builder.
1.Do your initial torque #125.
2.Warm engine to operating temp, let cool overnight. Do a retorque, loosen each nut one by one apply more moly and retorque.
3. Drive the truck with NO BOOST for one full tank (400-500 miles)
4. Let truck cool and do another retorque, Loosen nut one by one apply more moly and put back together.
5. Drive the truck and give her some boost, but no 1/4 mile runs for 1000 miles.
Do final retorque, and that should hold for a long time.
I was told the less hard you are on it between retorques the longer it will last.

schaef_12

I basically did 3 retoques already but i will do it again after a tank of fuel. I have the fuel turned all the way down, witch nets about 20 lbs of boost. Also, on the last retorque, i went to 145. Shouldnt be anyproblem with that right?

dieselman2300

I'm running #145 on mine, and I havent had any problems

schaef_12

Cool, Hopefully it will hold 40lbs of boost for awhile.

dieselman2300

Mines been holding 50. Just bought the S400 for the twins so we'll see if it hold 70.

schaef_12

Thats good to hear. You just have ARP's and and a 10 over marine gasket?

dieselman2300

ARPs and a 20 over.

schaef_12

I was going to do the 20 over, but i thought that i would have a tough time getting it started when it is 0*.

NoSeeUm

This is the purpose also of using the correct lubricant on the nut. The idea is to purely stretch (apply tension to) the stud. Of course, this done by twisting the nut. If the nut has some resistance to turning then the tension force on the stud will not be correct.

Jim

schaef_12

that makes sense, and I am guessing why the headbolts do not hold boost well, because they stretch