cylinder head bolt torque/failure

rrietman · Post by **rrietman** » Mon Mar 05, 2012 9:55 pm

here's one that I have not had happen before. torqueing up a head and this one started twisting at 18 (I normally go to 22-24 and always lube the threads). checked for the nut bottoming out (OK) . tried again and it broke at 21. granted it's the thin outer front, but still? I guess it was just tired after 50 years.
Randy

jensen · Post by **jensen** » Tue Mar 06, 2012 3:31 am

Hi,

The specified torque is always dry, not lubed. When you lube the thread, the torque is way to high. Make sure the threads are clean and dry, also the engine case threads.

I torque these dry on the specified torque, and after running once, I torque them again, and after a couple of 100 miles, I turn every nut 20 degrees further. Some people get the studs out with a gripper, or other pliers. Once the surface of the stud is damaged, the stud can snap under much lower torque than the specified setting, caused by tearing.

Jensen

G-Man · Post by **G-Man** » Tue Mar 06, 2012 2:41 pm

After 50 years you don't know what the history of that stud has been it may have been overtorqued on many occasions.

G

gbyoung2 · Post by **gbyoung2** » Sat Aug 29, 2015 5:23 pm

G-Man wrote:After 50 years you don't know what the history of that stud has been it may have been overtorqued on many occasions.

G

True that, and I know the CL77 engine I'm presently working on has been into at least once. I intend to kinda "sneak" up on the main head bolt torque and go from there - BUT - do have a question: what torque are ya'll putting on the 10mm nuts that sit under the plugs? Haven't found a spec for those in the Manual.

?????

OldScrambler · Post by **OldScrambler** » Mon Aug 31, 2015 9:17 pm

SNUG............my fore-arm tells me about 8-10 lbs................last on - first off

Ericvanrijn · Post by **Ericvanrijn** » Sat Sep 19, 2015 2:02 pm

jensen wrote:Hi,

The specified torque is always dry, not lubed. When you lube the thread, the torque is way to high. Make sure the threads are clean and dry, also the engine case threads.

I torque these dry on the specified torque, and after running once, I torque them again, and after a couple of 100 miles, I turn every nut 20 degrees further. Some people get the studs out with a gripper, or other pliers. Once the surface of the stud is damaged, the stud can snap under much lower torque than the specified setting, caused by tearing.

Jensen

And, what is the specified torque? It is not mentioned in my service manual! Can someone please help me with this info?

LOUD MOUSE · Post by **LOUD MOUSE** » Sat Sep 19, 2015 4:22 pm

Book shows:
13.74-16.63ft-lb.
I go 21. ........................lm

Ericvanrijn wrote:
jensen wrote:Hi,

The specified torque is always dry, not lubed. When you lube the thread, the torque is way to high. Make sure the threads are clean and dry, also the engine case threads.

I torque these dry on the specified torque, and after running once, I torque them again, and after a couple of 100 miles, I turn every nut 20 degrees further. Some people get the studs out with a gripper, or other pliers. Once the surface of the stud is damaged, the stud can snap under much lower torque than the specified setting, caused by tearing.

Jensen
And, what is the specified torque? It is not mentioned in my service manual! Can someone please help me with this info?