Replace the studs and nuts on that engine

May 1, 2017 | By Staff

Question:

While disassembling my old Jeep I lost a couple of head nuts that are 7/16-20 and .460” tall. My local nut and bolt shop has grade 8 nuts in shorter or taller versions. I opted for one .600” tall and then had second thoughts. The question is whether using a specified torque—70 lb.-ft. in this case—would be affected by additional threads? Will a given torque produce a different clamping force when using more or fewer threads? If the answer is yes, do we know how much and should I then replace all of the nuts?

Answer:

I would use the same nuts all around on that old engine, but I have a hard time picturing that more threads would mean more torque at a given setting of the torque wrench. It is possible that a few more threads might make the torque wrench pop off early due to increased friction, but that should be mitigated by the lubricant you use on the studs.

I generally replace the studs as well as the nuts on an old engine when I have it apart. Threads get stretched, and studs can narrow between the head and the deck from stretching and corrosion. Also, all the heat and cooling over the years may have a negative effect.

Purchase new studs and nuts from ARP, which—though a bit more expensive—are the best. And then I install them using ARP’s Ultra Torque lubricant, which is specially designed to help you achieve accurate pre-load on the nuts. Ordinary hardware store studs are not tapered properly and may not seal well, and their quality may well be less than desired. Also, ordinary motor oil will not give you the accuracy that ARP’s lubricant will provide when torqueing down heads. You can order new head studs, nuts and lubricant from:

ARP Bolts 1863 Eastman Ave. Ventura, CA 93003 | arp-bolts.com

I am aware that the above sounds like an endorsement for ARP products, but they don’t know me, nor do I know them. However, I have used their products on a number of occasions and have found them to be first rate. Extricating and going through an engine is a lot of work, so I tend to go the extra mile in order to make sure I end up with an engine that is as good as or better than new.

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Make sure head studs and nuts are clean and lightly lubed before you torque them down evenly according to the diagram in your service manual.