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Answers to Frequently Asked Questions

Do I need to re-torque my head bolts or studs?
If you follow the ARP installation instructions, there should be no need to do a re-torque. However, it may be necessary under certain circumstances if the gasket manufacturer’s instructions require it, particularly if a fire ring has been installed. ARP recommends not doing a re-torque on a hot engine.
Do I need lube on my bolts or studs?
We recommend using ARP Ultra-Torque lube to ensure an even, accurate clamp load and to prevent thread galling. This is particularly important for stainless steel fasteners. The lube should be used under the head of the bolt or the bearing surface of the nut and on the threads, unless a thread sealer is used.
Can I use Loctite or any thread locker instead of ARP Ultra-Torque assembly lube?
Yes, you can. Some engine builders use blue Loctite on the stud end that goes into the block. Do NOT use Loctite on the nuts for the head studs or main studs. Always ensure that the threads are clean prior to applying any lube. When using Loctite, make sure you assemble the parts before the Loctite cures. You can use Loctite instead of ARP Ultra-Torque, but do not use them together.
Do I have to use Ultra-Torque?
We spent two years developing ARP Ultra-Torque and we have come up with what we believe to be the ultimate fastener lubricant. All of our torque values are based on using Ultra-Torque. We do not provide torque values for use with any other fastener assembly lubricant (such as motor oil, moly lube, etc.) Use these other lubes at your own risk, as their use may lead to a part or engine failure, for which we are not responsible.
Do the threads of the bolts or studs going into the block need lube?
Yes. On blind holes use a small amount of ARP Ultra-Torque lube on those threads. Additionally, if the studs protrude into a water jacket, you will need to clean the threads in the block to remove all coolant and oil residue. Apply a liberal amount of ARP thread sealer or a high temperature thread sealer.
Are ARP bolts and studs re-usable?
Yes. As long as the fasteners have been installed and torqued correctly, and show no visible signs of damage, they can be re-used. If they show any signs of thread galling or corrosion, they should be replaced. In the case of rod bolts, if any of them have taken a permanent set and have stretched by .001” or longer, you should replace them immediately. See page 29 in the catalog for more detailed information on this critical measurement.
Do I install my studs into the block first?
After test fitting the studs in the block, it is generally easier to remove the studs, put the head gasket and head on the block and install the studs. This will reduce the possibility of damaging the upper threads of the stud and scraping the cylinder mounting holes. If the block has no alignment dowel pins, you can use the stud to align the gasket and head.
Does the chamfer on the inside diameter of the washer go up or down?
The chamfered side of the washer goes up, towards the head of the bolt. The chamfer is there to create clearance for the radius between the bolt shank and the bolt head.
Do the head studs only go in hand, or finger tight?
Yes, cylinder head studs are installed only hand tight. Other than the use of an allen wrench on the hex broached into the end of the stud (to ease installation, not to apply torque), use no tools to seat them in the block. However, it is extremely important to ensure that the studs are fully bottomed out in the hole in the block and not hung up on damaged or corroded threads in the block preventing the stud from being fully seated. This is often indicated when the stud threads extend past the deck surface.
I have heard that some people have had trouble with newly installed cylinder head studs leaking water. How do I make sure I don’t have the same problem with my new ARP head studs?
Prior to installing your new head studs, it is very important that you have clean threads on both the block and the studs. First, clean up all the threads in the block with a thread-cleaning chaser, NOT a regular tap. Thread chasers are designed so that they do not remove material from threads but merely remove debris and corrosion. Make sure you go all the way to the end of the threads in the bottom of the hole. Then clean out all the holes in the block with brake or carburetor cleaner to remove all the debris. Make sure the threads on the new studs are clean. Use a liberal amount of ARP thread sealer, high temp silicone or Loctite to ensure that there will be no air pockets that can cause leaks. Then follow the ARP instructions for installing the fasteners.
Are ARP’s torque recommendations the same as the vehicle manufacturer’s specifications?
Sometimes ARP will recommend using torque specifications that are different than the manufacturer, but not always. Our kits are engineered for specific applications, factoring in the necessary clamp load we’re trying to achieve, material type, block or head material, etc. To achieve our target clamp load, it may be necessary to use a different torque figure than what the factory calls out.
The torque/stretch number listed for my after-market connecting rod is different than what ARP calls out for the same bolt. Which specification do I use?
Refer back to the rod manufacturer and use their torque/stretch value.
What drill size do I need for my wheel studs?
To determine what drill size you need, you will need to know your axle/hub material and the wheel stud knurl diameter. If your axle/hub material is cast iron or steel, your drill size will be 0.005” smaller than the knurl diameter. If your axle/hub material is aluminum, your drill size will be 0.007” less than the knurl diameter. The Wheel Studs section in the catalog, pages 76 & 77, list the knurl diameter size.
What is the difference between ARP2000 and Custom Age 625+ studs?
ARP2000 is an alloy steel that has a tensile strength of 220,000 PSI. Custom Age is an austenitic alloy that has a tensile strength of 260-280,000 PSI, providing a greater clamping force than that of ARP 2000.
Why does L19 material require special handling?
Like most high-strength quench and temper steels, L19 requires special care to avoid hydrogen embrittlement or stress corrosion. The material is easily contaminated and subject to stress corrosion. The parts must be kept well oiled at all times and not exposed to moisture. Wearing gloves while handing L19 parts is a good precaution.
I have heard that the black oxide bolts and studs I get from ARP will eventually rust. Is this true and if it is, can it be prevented?
Yes, the bolts or studs will rust. Black oxide is a conversion coating formed by a chemical reaction with the iron in the metal to form an integral protective surface. It is NOT a permanent coating that has bonded to the surface of the fastener. The black oxide process is a short-term rust preventative only and any part exposed to the atmosphere will show signs of rust in a matter of days. Frequent application of oil to the part will increase corrosion resistance. In addition, the bolt head could be painted with black epoxy primer, followed by semi-flat paint or clear lacquer.
What is an U/C stud?
An U/C stud is “undercut”. This means the shank diameter is smaller than the minor diameter of the thread. This eliminates the stress being concentrated on the upper portion of the threads and spreads it over the length of the stud. In some applications, it also increases compliance in the stud to forces of expansion, decreasing distortion of the assembly at operating temperature.
Do I need head bolts or studs for my engine?
It depends on the installation. On many street-driven vehicles, where the master cylinders for example might protrude into the engine compartment, it’s probably necessary to use head bolts so that the cylinder heads can be removed with the engine in the car. For most applications however, studs are recommended. Using studs will make it much easier to assemble an engine, as the stud will act as a guide, ensuring proper alignment for the head and gasket. Studs also provide more accurate and consistent torque loading. See page 38 of our catalog for more discussion on the topic. For help in deciding what is best for your application, please call our Technical Support desk at 800.826.3045.
I have heard that the black oxide bolts and studs I get from ARP will eventually rust. Is this true and if it is, can it be prevented?
Yes, the bolts or studs will rust. Black oxide is a conversion coating formed by a chemical reaction with the iron in the metal to form an integral protective surface. It is NOT a permanent coating that has bonded to the surface of the fastener. The black oxide process is a short-term rust preventative only and any part exposed to the atmosphere will show signs of rust in a matter of days. Frequent application of oil to the part will increase corrosion resistance. In addition, the bolt head could be painted with black epoxy primer, followed by semi-flat paint or clear lacquer.
Do I need lube on my bolts or studs?
We recommend using ARP Ultra-Torque lube to ensure an even, accurate clamp load and to prevent thread galling. This is particularly important for stainless steel fasteners. The lube should be used under the head of the bolt or the bearing surface of the nut and on the threads, unless a thread sealer is used.
Can I use Loctite or any thread locker instead of ARP Ultra-Torque assembly lube?
Yes, you can. Some engine builders use blue Loctite on the stud end that goes into the block. Do NOT use Loctite on the nuts for the head studs or main studs. Always ensure that the threads are clean prior to applying any lube. When using Loctite, make sure you assemble the parts before the Loctite cures. You can use Loctite instead of ARP Ultra-Torque, but do not use them together.
Do I have to use Ultra-Torque?
We spent two years developing ARP Ultra-Torque and we have come up with what we believe to be the ultimate fastener lubricant. All of our torque values are based on using Ultra-Torque. We do not provide torque values for use with any other fastener assembly lubricant (such as motor oil, moly lube, etc.) Use these other lubes at your own risk, as their use may lead to a part or engine failure, for which we are not responsible.
Do the threads of the bolts or studs going into the block need lube?
Yes. On blind holes use a small amount of ARP Ultra-Torque lube on those threads. Additionally, if the studs protrude into a water jacket, you will need to clean the threads in the block to remove all coolant and oil residue. Apply a liberal amount of ARP thread sealer or a high temperature thread sealer.
What drill size do I need for my wheel studs?
To determine what drill size you need, you will need to know your axle/hub material and the wheel stud knurl diameter. If your axle/hub material is cast iron or steel, your drill size will be 0.005” smaller than the knurl diameter. If your axle/hub material is aluminum, your drill size will be 0.007” less than the knurl diameter. The Wheel Studs section in the catalog, pages 76 & 77, list the knurl diameter size.
Technical Support
You can always call us with your questions, but you can use these resources to try and find an answer first.






Phone Hours: M-F 7:30a-4:30p PST
800-826-3045 or 805-339-2200

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ARP achieved ISO 9001:2008 and AS9100 registration in 2009 and has maintained them since that time. These registrations represent ARP's unwavering dedication to producing quality fasteners, continually improving our quality management system and delivering total customer satisfaction.