Head bolt torque

[Toddshog]

After replacing the headgasket in my 1.6 I tried to torque the head according to the Bently manual. After the torque wrench I tried the 180 degree turn with a 12" breaker bar and 1/2 way through realized...... mistake! I made it to about 175 degrees then had to reposition and tighten a little more realizing the book says "in one motion" So, worried about this I then went to a cheater bar, at bolt #7 it came off so I backed off all the bolts.

Questions:

Do I need to buy a new head gasket before trying again?

Do I need to buy new stretch bolts?

The engine was never heated for the final 1/4 turn.

Thanks,
Todd

[Master ACiD]

i have only done a stretch bolt head once, but if i remember correctly you are suppose to drive the engine for some miles before doing the final torque right?

[fspGTD]

The 1/2 turn movement in one motion as mentioned in Bentley is pretty tough.  I personally wouldn't worry about 175 degrees versus 180 degrees if you hadn't loosened them.  The whole point is that you're yielding the material of the bolt to ensure it has reached maximum possible tensile load, dictated mostly by the material and dimensions of the bolt, and relatively little by the torquing or rotational accuracy.  There is probably a wide area of angle that would probably work, and certainly 5 degree precision is not necessary.  (Although it can't hurt to try and get close as you can.)  Anyway, what I usually do in place of the single 180 degree turn step are two sets in sequence of 1/4 turns.  That is also the procedure you see printed on the side of some of the proper head gasket packages.

A breaker bar with a really long handle is the right tool to use here.  Use only enough socket extension as is necessary to clear everything during your swing.  Just throw some weight into them...  Show those bolts who's boss. :wink:

I also like the lubricate the bolt threads with moly CV joint grease, makes them go in and come out much more smoothly.  Although that is not necessary.

Sorry, but it seems the bolts you've loosened after being yielded should be replaced with new if you want confidence the job is done right.  Otherwise you may tighten them too little, or over-yield them when trying to re-tighten the loosened, previously-yielded bolts.  They are available for as little as $1.25 per bolt so it's probably not worth risking.

[Toddshog]

I was thinking the same, cheap insurance instead of having to pull the top again so off for another head gasket and bolts. What ever happened to using a torque wrench and standard bolts?

If one is indead "streching" the bolt, I am assuming the tensil strength of these bolts must vary bolt to bolt then would this not put an uneven stress or torque on the head? As tight as these bolts are, I am guessing that 5 degrees coul be as much as 15-20# not counting the possibly differences in the bolts.