Head retorque advice

[mike ellis]

After covering a few hundred miles on the new engine (four cylinder) I am about to retorque the head. My normal procedure and that which I have been recommended in the past is to slacken the nuts by 1/4 turn and then retighten to 100-105 ft lbs but recently someone has said not to bother slackening but just check with torque wrench and tighten where necessary.

 

Which is your preference and indeed does it matter?

Edited October 22, 2013 by mike ellis

[AlanT]

When we had to help someone recently with a stripped block I looked up the torque standards for 1/2in UNC and UNF bolts.

 

The top grade of UNC bolt has a torque value of 110 ft.lbs according to some data. This is if you did'nt lubricate the thread.

 

You are working on a cast block and this will be a good bit less and the metal is old now.

 

Be careful not to overdo these. Fixing the block is a PITA.

[RogerH]

Hi Mike,

Alans warning is fair, we are dealing with old stuff. However if you undertorque the head you may blow the gasket.

Torque as per TRiumph manual - if it goes pop then so be it.

 

Slacken/ re-torque is an acceptable method.

 

Roger

[Ashley James]

I had to build my engine into another block because there were cracks between the stud holes and the water jacket, two of them, one at each end on the distributor side. Be careful and TBH I see no logic to backing them off and re-torquing them, just see if they'll pull down a bit more. That's how I was shown and what I've been doing for fifty odd years now. Seems to work.

[Motorsport Mickey]

Roger is correct, slacken off the head nuts first (1 flat only) otherwise the torque reading may be incorrect.( A measure of the torque applied will be taken up overcoming the "stiction" of a nut which has been in situ in it's fixed position for a while, even if only a matter of hours/day). Then run the nuts up in a smooth movement to the torque setting, 105 lb ft as per the manual. (cleaned dry threads, DO NOT lubricate).

 

In my race engines I took them up to an indicated 110 lb ft without a problem, and as Roger says if the block or studs/nuts won't take the 105 lb ft standard setting then you are better off finding out in the garage rather than halfway to Invercockieleaky or whatever.

 

I slack off the nuts/bolts on my Stag at the beginning of every motoring year (on a Stag an action akin to juggling with razor sharp knives !) and retorque the engine. Although as a sop to my weavily thoughts I do drop the water from the system first to help avoid any possibility of a water seepage.

 

Also Alan says he's checked the torque capacity of 1/2" unc bolts which is 105 lb ft , but I regard these items as not being what we are using. We are using studs which are screwed into the block by hand and then the torque is applied on the opposite end of the stud through a nut , I was always taught that bolts and nuts apply their torque in different ways. The finer thread of the nut clamping the head and the lack of any torsionial losses through the stretching action which would apply throughout the shank of a true bolt giving a truer reading.

 

Mick Richards

Edited October 22, 2013 by Motorsport Mickey

[mike ellis]

Many thanks for the replies. Job now done.