Head bolts keep stretching

[DaddyLoafin]

I’m putting my 787 back togesther and when I go to tighten the head bolts to 30ft lbs 1 hole keeps stretching bolts. I took it apart to see if I could see anything and now I have another 2 that won’t hit 30ft lbs no matter how much I turn them. They hit 15 ft lbs on the first go through but won’t ever hit 30.
Am I missing something or am I just having a lot of bad luck with these bolts?

Also The head was milled so Idn if that has anything to do with it

 

[mikidymac]

The head bolts only get tightened to 17 ft/lbs. Grease on the threads and loctite 242 under the heads.

Hopefully you didn't damage the head or threads going that high but it is likely.

 

[DaddyLoafin]

Ahh I see what I did. I did do the grease and loctite but for whatever reason used the wrong torque numbers. Thank you

 

[mikidymac]

The cylinder bolts are 30 ft/lbs. That is my guess.

 

[DaddyLoafin]

The cylinder bolts are 30 ft/lbs. That is my guess.

Lol also working from memory in a less than sober state.
So the heads fine, I haven't run a tap through the threads again yet, but I assume they're fine but all but 2 of the bolts stretched about 0.040 so now I'm waiting on replacements.

 

[mikidymac]

If you have one, a thread chaser is better than a tap. A tap typically removes some material.