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View Full Version : Cylinder Head Bolts Undertorqed


brotherM
11-03-2009, 05:51 PM
I've just replaced the cylinder head on my 93 525i. I bought new bolts, cleaned out the block bolt holes and lighlty lubricated the new bolts. I tightened them to 22 ft. lbs. as instructed, then tightened each 90 degrees more as instructed but I was unable to tighten each another 90 degrees as instructed. When trying to get the second 90 degrees, I was struggling to even get them 45 degrees with an 18 inch torque ratchet. I was afraid they would brake to I set the torque on the ratchet to 60 ft. lbs. I torqued them all to 60 ft. lbs. instead of risking breaking the bolts by trying to tighten them to the second 90 degrees. Does anyone know how much torque these bolts can take before breaking? If I only tightened the bolts to 60 ft. lbs and to about 45 degrees on the second torque angle tightening, am I up for blowing a head gasket?

ffej
11-03-2009, 05:55 PM
I have too much experience in tightening head bolts and I have to say....grrrrrrrrrr.


You really should follow the proper procedure for torquing. My experience, though is that the second stage of 90-degree torque is not easy. That said, you may not have a problem. And, hey, if you like doing the headgasket, no big deal :eeps:

brotherM
11-03-2009, 06:21 PM
Wow, quick reply, nice forum. Did you ever break a head bolt on the second 90 or strip out the block threads? I looked up what a normal T12 bolt can be torqued to and around 57 ft. lbs. was the max in my black book.

ffej
11-03-2009, 08:56 PM
Wow, quick reply, nice forum. Did you ever break a head bolt on the second 90 or strip out the block threads? I looked up what a normal T12 bolt can be torqued to and around 57 ft. lbs. was the max in my black book.

I didn't, but the head bolts aren't "normal" T12 bolts. They're designed for a 1-use, stretch application, so they can handle a higher torque load than a standard bolt.

As most of my racer/builder friends say "just run it til it breaks and rebuild it then" :)

Good luck!

E36 Phantom
11-03-2009, 10:13 PM
+1 to FFEJ. I did a bunch of research on head bolt torque when I had the Supra and the blown HG then.

Head bolts are "torque to yield" and not reusable. You won't break them.

ross1
11-05-2009, 09:08 AM
Are you certain the bolt holes were dry and clean? Oil sitting in the blind holes will cause hydraulic pressure and inhibit proper tightening.
More important than a specific torque reading is that the clamping pressure be even.
65 is too low, if you are going to use a number I'd be closer to 85 or 90 #.
The bolts are one time use after they have "yielded". Same with the gasket once crushed.
"Yield" in this case means the bolt permanently deforms(stretches), I doubt 65# did this. I'd go back and snug things up to 90#. The gasket can be crushed further.
As long as you have even tightening, straight surfaces and a good quality gasket you'll be fine.