What Every Rebuilder Should Know About Head Bolts, Rod Bolts Studs And Fasteners: Knowing what type you're working with will determine if and how it can be reused

      There are three types of procedures used for torquing: torque to yield/angle to turn; torque to maximum stretch yield; and torque to a specific torque number and hope it's correct.

      If cycling is not done properly, especially before machining, your dimensions will change drastically in the cylinder bore, cam tunnel and main bearing housing bore. I have seen these dimensions change anywhere from .0004" to .0015" and the size gets smaller not bigger.

      The importance of cleanliness, correct thread chasing and lubrication is very critical. There is a lot of controversy regarding the reuse of one-time-only torque bolts. The reuse of aftermarket fasteners like ARP, B&B, Manley, Milodon, Moroso, Mr.Gasket, SPS, etc. are fine to reuse for many times due to the higher quality and designs of these bolts, and their higher material heat treatments compared to standard type construction fasteners. Nearly all aftermarket fasteners are made to aircraft quality specs using a "J" thread design which is flat at the root of the thread pitch.

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This is a clear photo of a "J" type thread used by high performance fastener manufacturers. This explains why you can't use a die to fix any damaged threads; the root of the thread is nearly square.

      On aftermarket studs or bolts, never use a die to re-cut the threads. When you clean the threads in the block, heads and rods, never use a tap from a conventional tap and dye set. The use of thread chasers, both male and female, are recommended. The best thread cleaning chasers I have seen are made by ARP in Oxnard, CA. They look like taps, but are ground undersize to eliminate the removal of too much material in the threaded areas. ARP has thread chasers in U.S.S. coarse (1/4", 5/16", 3/8", 7/16" and 1/2") and they clean thread holes great.

 On aftermarket studs or bolts, never use a die to re-cut the threads. The use of thread chasers, male and female, is recommended.

      Studs, bolts or nuts should be able to be screwed by hand with no exerted force. The cleanliness of faster installation is very important. Do not clean threads, studs, nuts, bolts, etc. in oily solution. I recommend using clean solvent, brake cleaner or any other type of oil-free parts cleaning solution. Always air dry fasteners; do not use rags.

      Torquing is a procedure to obtain maximum clamping force of two parts or surfaces. To obtain this you are overcoming the friction of two surfaces: the fastener and the threaded hole. I recommend the use of a good lubricant and/or thread sealer when going into a water or fluid type area.

      If you are using moly or an anti-friction lube instead of oil, use about 20% less torque. Always use the manufacturers’ recommended torque and lubricant. Usually all good aftermarket fastener manufacturers will supply their preferred moly lube or sealant for their fasteners.

      When you resurface or deck a cylinder block, always rechamfer the surface with a chamfering tool between 60° and 70°. This is especially important when using replacement head studs. If this isn’t done, there’s a possibility of stud failure because the sharp edge of the block is cutting into the stud causing a stress fracture on the chamfer of the stud.

If you’re using high performance cap screw rod bolts (NF) the use of a Snap-On or other high quality re-threading set is recommended.

If you need to repair or weld a bolt hole in your block or cylinder head rocker stud boss, always drill and tap the hole with a GH-3, 3B series tap when using aftermarket high performance fasteners. Never use “liquid locking-type” products on studs, nuts or bolts to secure them in place. These products break free under heat and are not recommended. I like the use of Teflon based tapes and sealants in water and fluid type areas. They also reduce friction while torquing.

Most people don’t know how to torque fasteners properly. Furthermore, most torque wrenches are so far out of calibration it’s not even funny. I always recommend a quality brand name calibration clicker torque wrench or a dial-type for real accurate torquing. Always recalibrate your clicker-type wrenches every nine to 12 months. Never use your torque wrench for a ratchet or breaker bar to loosen nuts and bolts. It makes them go out of calibration too quickly.

For consistent, accurate torquing, always use a quality, brand name calibration clicker torque wrench or a dial-type wrench. Be sure to recalibrate clicker-type wrenches every nine to 12 months.

When you torque anything, keep the torque wrench at about two o’clock and pull the wrench to three o’clock. Do not pull past this point because your angle will get too far off. This is when you pull past your torque point and over-torquing takes place. Always pull into your torque range, not past it.

The correct angle to hold the torque wrench is shown above. For best results, it should be held at the two o'clock position and pulled to the three o'clock position.

On all performance fasteners you must cycle the bolts or studs four or five times before any machine work like boring or honing can be done. If you’re using torque plates, use the same fasteners and gaskets, especially if you’re using a hard or soft wire o-ring gasket. If this isn’t done, as much as 0.0004” to 0.0015” less diameter will be noticed. If you don’t torque cycle the main caps four or five times, between .0002" and .0007" less diameter will be noticed.

High performance head, main, or rod bolts always have a radius under the head of the bolt. Make sure on high performance head and main bolts that you use a chamfered washer so you don’t bind up the bolt. This will cause a failure by either coming loose or breaking the washer. If you spot-face your rod cap pads where a cap screw rod bolt would be tightened, make sure you chamfer the cap so the radius under the head of the bolt won’t bind in the hole of the rod cap. If this area doesn’t have a suitable chamfer, the rod bolt will come loose or break from fatigue.

On I-beam rods that have a rod bolt stud type that’s pressed in, make sure you also have a radius for under the head of the rod bolt. If you spot face and chamfer the cap end on the I-beam rod don’t use a large chamfer; leave plenty of material so the rod nut has a good surface area to be torqued against.

Always lubricate bolts, nuts, washers (both sides) studs and any surface you are torquing against. Remember torquing is overcoming friction. When using aftermarket rod bolts (stud or bolt type) always torque to the stretch dimension, not the torque specifications. Under-torquing will cause just as many failures as over-torquing. When your rod bolt is torqued to a specific torque reading, odds are the bolt is under-stretched.

We have used many rod bolt torque specs of 60 to 65 lbs. that are supposed to stretch the bolt .0058” to .0063” and it only stretched the bolt 0.0034”. Usually it will take between 80 and 94 lbs. to obtain the proper stretch. Buy yourself a rod bolt stretch gauge. You will be surprised how far off you have been. And always follow the torque sequence supplied by the manufacturer; otherwise you won’t achieve your maximum clamping force.

The rod bolt stretch gauge is a very important tool in the rebuilder's arsenal.

Once a non-“J” type aircraft quality bolt is torqued to a specific figure, then stretched another 30° to 80° to stretch it to maximum yield and clamping force, I fell they should be thrown away. New ones should be used each time the heads are changed. If you are angle torquing there are several angle gauges I recommend. Fel-Pro, K-line and Snap-On are real good. I’m sure there are many more good ones out there. I use these at my school.

These are examples of angle-to-turn degree indication gauges that are used at Mondello Technical School. There are many other quality products available as well.

I feel torquing to a specific torque number is really looking for trouble, especially if you use the wrong lubricant. You must always cycle your fasteners (or torque to yield, angle to turn) every nut, bolt or stud that you tighten.

A fastener is used to obtain maximum clamping for a better sealing, longer lasting engine. Cycle your engine fasteners for a longer engine life. These procedures will definitely help you build a better engine. And always remember, we make horsepower, not promises.