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- 22.
How can I deal with head or manifold studs which fail to hold the specified torque values (35 foot-pounds for the head, and 25 foot-pounds for manifolds)? - Top
- There are several methods of dealing with studs which will no longer hold proper torque, depending on how badly the threads in the block are damaged:
1) If you stop torquing as soon as a particular hole starts to feel "soft", you could re-tap to 10 mm coarse threads and install one of our 10mm head studs. The 10mm tap is the largest tap that will go through the original holes in head, which means that this technique could be used without removing the head. Our 10mm studs are machined so as to retain 3/8" fine threads on the upper end.
2) Unfortunately, by the time a stud is felt to be failing, it is usually too late for the 10mm solution. In these cases, it is necessary to remove the head and re-tap the failed holes to 1/2" by 13 (coarse threads), and to then install one of our thread repair bushings (product number OBLK_09_114).
NOTE: See below for "text-only" instructions to assist in installing these bushings.
3) Helicoils can be used in place of solid repair bushings; however, it is somewhat more difficult to seal the "coil" design of Helicoils and prevent water from the cooling jacket from working up past the threads of the studs.
4) Some folks have drilled out the holes in the head so as to accommodate the use of 7/16" studs. While I have no serious issues with this practice, we have no data on how to adjust the torque value for the larger thread diameter, nor do we have any source for appropriate 7/16" studs.
5) As a final thought on this subject, it's very important to thoroughly inspect the threads in stud holes prior to assembly (an ounce of prevention is worth a pound of cure). In the case of holes in which the threads are observed to be effected by corrosion, damaged by over torquing, or simply exhibit a "sloppy" feel, we recommend the use of JB Weld to give the threads a little additional strength, and then (in the case of heads) only torquing the nuts to 30 or 32 foot-pounds - even the ones which were not suspect.
Universal technical folks have told us some years ago that they have considerable test data which show that 30 foot-pounds of torque on head studs retains a good safety margin.
INSTRUCTIONS FOR INSTALLING REPAIR BUSHINGS:
1) Drill out the failed hole(s) to 7/16", then tap for 1/2" X 13 (coarse) threads. It's critically important to keep the tap straight as you work. A small carpenter square is helpful. It's usually possible to "adjust" the tap as you go, in the event that you discover it is leaning a bit one way or the other.
2) Thread the bushing onto the end of a new stud, and dry run it into the hole a few times. You can double-nut the stud to make it easier to turn it in, but be very careful to not get the bushing stuck in the hole at this point. If it gets tight at all, go back in with the 7/16" drill and "worry" the hole a bit larger by wobbling the drill a small amount. Continue to check the bushing for fit, and when you can install it almost all the way in using your fingers, you're ready for the next step.
3) Smear some JB Weld around the outside of the bushing and around the inside of the hole in the block.
4) Turn the bushing in using a wrench on the double-nuts until only the small round shoulder is exposed outside the hole.
5) The bushings have 4 small slides around the outside, which get tapped in between the bushing and the block after the bushing is finally set in place to keep it from turning. Don't worry if one (or even two) of these slides breaks off. Any two slides should hold it in place while you remove the stud.
6) Grind, or file, the top of the bushing flush with the surface of the block. If you can get your hands on a small hand-held grinder, it makes this part of the job much easier.
7) It's best to dry run the head or manifold over all of the studs before the JB Weld has had a chance to set up. It is sort of a good thing if your bushing ends up having a small bit of wobble, so that if the stud is just a bit less than perfectly straight, the head or manifold can bring it into alignment. You can even install the nuts, but only hand-tighten them until the JB Weld has had a chance to fully cure (usually overnight). - Updated:
November 6, 2003
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