Technical Torque angle

[fmorelli]

A post made yesterday made it on my morning reading list, while the coffee pot is warm and no one is up yet. Someone had mentioned re-torquing head bolts. Most modern head bolt configurations, to my knowledge, are run to a snug torque then torque angle is used to stretch the bolt. These do not get re-torqued as best as I knew. I just did a Nissan head and swapped the bolts to Torx (a better fastener by design) and had gone through this exercise. I'm not an engine builder, but having done a few head installs this year, and felt I needed to brush up. I wanted to pass along this short document as I suspect a number of you guys will find this interesting.

Filippo

 

[Jeffman]

Thanks. Looks like an informative and interesting read.

 

[iminhell1]

I might read it later.
But what I've found multiple times both in things I've fixed and helped others with ... threads need to be dry and clear. Many times a need to retorque is due to threads being filled with coolant, oil, solvent. When you turn the bolt/stud in you're compressing this fluid and it's giving an artificial torque number.
It's actually the same with virtually any fastener. Dirty threads will get you every time.

 

[fmorelli]

I couldn't agree more with your comment!

Filippo

 

[Alex@abrhouston]

threads need to be dry and clear.

Some repair procedures recommend a clean and dry bore, as the bolts are pre lubricated.

Did the manufacturer specify this request?

Some say "do not wash off oil and/or re-oil bolts"

As a general rule- what your describing would be when a bolt is going into a hydraulic state, as there is byproduct at the bottom of the bolt hole (coolant/oil/etc) and will either rip out the threads, blow the bottom out of the hole, or give an incorrect torque value.

As a general rule- ALL FASTENERS require lubrication, unless otherwise stated.
Some repair procedures specify clean threads, and light oil on the bolt or fasteners.
At the end of the day, its all on the application.

 

[fmorelli]

Alex, thanks for clarifying. I read his comment as residue scenarios, not pre-lube, etc ... but you bring up an excellent point!

Filippo

 

[iminhell1]

But how much lube? What is not enough and what is too much? Where does the extra go?

Every time I've done ARP head studs (about a dozen times) I've followed their guide. But I don't install the head the same day. I'll turn the studs into the block and let them rest for a solid overnight. Come back and there's always lube or fluid around the top to the threads. If I wouldn't let them sit then that excess would have to go somewhere sometime.
I don't know if that's standard practice but I'm happy with how I do things. haven't had any HG failures or backing out of anything.


Had a Conquest years back I did a SCE copper HG on with ARP studs. Was no TQ recommendations at the time so I had to wing it. Really took my time and let everything settle. Turned out beautiful and held plenty of abuse. Was my first and only time using a copper head gasket.


It's hard to convey too little and too much over the internet, especially when dealing with people who's mechanical aptitude you don't know.

 

[Chris@VargasTurboTech]

Good stuff! Generally I keep bore clean/dry, then apply lube of choice to fastener, wipe excess with a calibrated rag, then install. Back in the day on submarines we'd use a sweet little dos-type program called PC Bolts to calculate required torque depending on clamping load needed, materials, size, lube, etc. It's amazing what a difference a little lube makes (!!!).

 

[fmorelli]

Calibrated rag, eh? Angstroms?

Filippo