Retorque Head Bolts

[8DC]

May be a bit of a beginner question for this forum, but what is the proper procedure to retorque the head bolts?

 

Do you back them off one at a time or all at once in reverse sequence?

Back them out until they are loose or just a turn or two?

If one by one, do the two small bolts in the timing cover need to be removed prior to doing this (I know it's important to remove them first when removing the head)?

If done one by one, do you loosen and retorque in sequence or reverse sequence?

 

Thanks!

[ctc]

FSM says to fully tighten bolt initially and after several minutes of operating the engine re-tighten if necesaary. I take this to mean that you would not lossen them, simply re-torque in the correct sequence.

 

I will let others enlighten me if I am misunderstanding the FSM.

[8DC]

FSM says to fully tighten bolt initially and after several minutes of operating the engine re-tighten if necesaary. I take this to mean that you would not lossen them, simply re-torque in the correct sequence.

 

I will let others enlighten me if I am misunderstanding the FSM.

 

Thanks for the reply, this is what I did after putting my head on and running the coolant through it yesterday.

...but I have this feeling that something isn't right because I always thought that the retorquing process required you to back the bolt off a bit before retightening because the friction of the tightened bolt head would require more torque to get moving than the amount you were torquing the bolt to. To get an accurate reading, you would need to back the bolt off a bit, right? Or is that already figured into the 61 ft./lbs. final torque?

[TimZ]

Thanks for the reply, this is what I did after putting my head on and running the coolant through it yesterday.

...but I have this feeling that something isn't right because I always thought that the retorquing process required you to back the bolt off a bit before retightening because the friction of the tightened bolt head would require more torque to get moving than the amount you were torquing the bolt to. To get an accurate reading, you would need to back the bolt off a bit, right? Or is that already figured into the 61 ft./lbs. final torque?

 

Your suspicion is correct - it's not figured into the torque spec. I always back each bolt off approximately an eighth to a quarter turn, then re-torque to spec. Basically you just need to back off enough so that you will be able to see it turn a bit as it comes back up to spec. Don't back them all off at once - do them in sequence. Back the first one off, re-torque it and then go to the next one.

 

Also, avoid re-torquing while the engine is still warm - you don't want it cooling down and changing temperature while you are doing this. Most recommendations that I have seen say to let the car sit overnight before re-torquing. This way you know that the engine's temperature has stabilized.

[Tony D]

Thanks for the reply, this is what I did after putting my head on and running the coolant through it yesterday.

...but I have this feeling that something isn't right because I always thought that the retorquing process required you to back the bolt off a bit before retightening because the friction of the tightened bolt head would require more torque to get moving than the amount you were torquing the bolt to. To get an accurate reading, you would need to back the bolt off a bit, right? Or is that already figured into the 61 ft./lbs. final torque?

 

This is exactly, 100% correct, and is exactly what is meant by 'retightening'---back off maybe 1/4 turn and then bring back to torque specification -- One at a time. Some say up until you know oil has gotten underneath, but it should still be there from original assemble and not be displaced after a short stint of startup and run in.

 

Under-Head friction accounts for roughly 75% of the rotary resistance you are measuring as 'torque'---breakaway can be 10-15% above set tension, in addition to relieving thread friction which may increase due to the threads 'settling' during the heat cycle of startup and run in.

 

Do it at an 'equalized temperature' state. We have a HELL of a time with our field people torquing (stud tensioning) our impeller bolts while still hot. They are supposed to be back to room temperature before final torquing--doing this is wise with the head bolts as well.

Edited June 30, 2012 by Tony D

[8DC]

Thanks to both of you!

I'm off to retorque my bolts.