Cylinder Head Bolt Torque Specifications

#Cylinder Head Bolt Torque Specifications Professional Invoice That

(what we use, your mileage may vary) Cam Sprocket bolt: 50 ft-lbs. (Chrysler spec) 130 ft-lb. Harmonic Balancer bolt: 180 ft-lb.

Cylinder Head Bolt Torque Specifications Professional Invoice That

So what went wrong?While there are many possible things that could have gone wrong, in our hypothetical example however, the most likely cause is the fact that the cylinder head was not torqued down properly. The radiator was also chemically cleaned, and there are no historic fault codes present. Moreover, to prove that the job was not performed by a backyard mechanic, the customer presents a professional invoice that clearly shows all the required engineering and tests had been performed, and that the water pump, thermostat, and radiator hoses were replaced at the time the original gasket was replaced. Nm Engine Designation Torque TVT FOUR-CYCLE LARGE FRAME ENGINE SERIES (CAST IRON BLOCK HH, VH and OH) Connecting Rod 86-110 10-12.5 Cylinder Head 180-240 20.5-27 Mounting Flange & Cylinder Cover 100-130 11 The customer maintains that the engine did not overheat at any point from then until now, and that the cooling system had not lost any coolant during this time.

Yield strengthYield strength refers to the tensile force that must be applied to a bolt in order to bring about a specified amount of permanent deformation in the bolt. On critical engine and suspension bolts, the proof load typically ranges from 85% to about 95% of the boltsвЂ™ yield strength. Put in another way, the bolt must remain in its elastic phase when a specified proof load is applied to the bolt. Proof loadProof load is always expressed as a unit of force, such as Newtons (N), or pound-force (lbf) and as such, it is one of three mechanical properties that define the overall tensile strength of a bolt, the other two properties being yield strength, and ultimate strength.Essentially, вЂњproof loadвЂќ refers to the maximum allowable tensile force a bolt can endure without that bolt suffering plastic deformation. Therefore, if the specified preload is not applied to all the cylinder head bolts equally, it is almost certain that one or more issues such as fatigue failures of one or more bolts can occur, or vibration can cause one or more bolts to loosen themselves, leading to a failure of the joint. As a practical matter, the total clamping force across an unloaded bolted joint, such as a cylinder head being clamped to an engine block, is assumed to be equal and opposite to the preload of all the bolts.

In practice, this meant that if the correct torque value were applied to, say, all the cylinder head bolts, the bolts would each have stretched sufficiently to supply the clamping force required to reliably seal the gasket against both the cylinder head and the engine block.It should be noted that even though conventional bolts stretched somewhat during the tightening process, their yield strength was never exceeded, which meant that these bolts regained their original length when the preload was removed. So what does it all mean?As a practical matter, all of the above can be applied to conventional engine bolts that merely had to be tightened to a specified torque value to supply the required clamping force in engines that did not consist of different materials, i.e., both the engine block and cylinder head(s) were made from cast iron.On these engines, all parts of the engine expanded at the same rate when they were hot, and contracted at the same rate when they cooled down. Ultimate strengthUltimate strength refers to the maximum tensile force a bolt can endure without breaking.

Note that this dividing line is a function of the combined effects of several factors, including the torque being applied to the bolts, the material the bolt is made of, the presence (or absence) of coatings, plating, or lubrication on any part of the bolt, the pitch angle of the thread, as well as the diameter of the bolt.All of the factors listed above, in addition to some that are not listed, have been incorporated into something called the вЂњNut FactorвЂќ, which is commonly expressed as вЂњKвЂќ in engineering speak. It is in this condition that the bolt supplies the required clamping force to hold the cylinder head down securely.The dividing line between the elastic and plastic phases is called the yield point, hence the term, вЂњtorque to yieldвЂќ bolt. It is important to remember that in the elastic phase, the bolt will not provide sufficient clamping force to hold the cylinder head down reliably.As the load is increased to the bolt, it undergoes a plastic phase, which means that the bolt is stretched to a point from which it cannot regain its original length should the load on it be removed. Thus, to address the problem with differential expansion/contraction rates, engine designers were forced to develop bolts that could be preloaded to their yield strength without breaking these bolts being known as- Torque to yield / Angular torque boltsAs with conventional bolts, torque to yield bolts are also tensioned until they deform, but with the major difference that torque to yield bolts are tightened until they are permanently deformed, which from our perspective as mechanics, is the most important characteristic to keep in mind, and here is why-When a torque to yield cylinder head bolt, or for that matter, any other critical torque to yield engine bolt is tightened, it undergoes two important phases, these (for our purposes) being the-In this phase, the bolt is stretched as torque is applied to it, but should the torque be removed the bolt will return to its original length.

Apply a further 90 degree rotation to all bolts in the proper tightening sequenceNOTE: The example of a tightening procedure above is just that, an example that is intended for illustrative purposes. Apply a 90 degree rotation to all bolts in the proper tightening sequence Tighten all bolts in sequence, and in two stages to a snug torque value of say, 30 Nm For example, a typical cylinder head tightening sequence might look like this- At this point, the bolt is over stretched (if it does not break first) and most, if not all of the clamping force supplied by that bolt is lost, which brings us to the next point- How to tighten torque to yield boltsLike conventional bolts, torque to yield bolts are also tightened in a specific sequence and prescribed number of stages to prevent distortion of the cylinder head (or any other components), but with the very important difference that the initial torque setting, which is known as the вЂњsnug torqueвЂќ is always relatively low.

The primary reason for the large disparities when using purely torque values involve the wide dispersion rates (also known as preload scatter) of torque values that are mainly the result of the overall coefficient of friction, which is a function of the combined friction under the bolt head and between mating threads.In practice, torque to yield bolts that were tightened properly will hold a cylinder head down securely for the life of the engine, barring of course, disasters such as overheating of the engine, since the yield point of the bolts were designed to cope with differential expansion/contraction rates that cause relative lateral movements between components. Applying degrees of rotation, as opposed to a torque value, also eliminates under or over tightening caused by poorly calibrated torque wrenches, since the angle of rotation is independent of the torque being applied.As a practical matter, it should be noted that by applying degrees of rotation to cylinder head bolts, the final clamping forces achieved would generally be within 10% of the specified yield points, whereas with a simple torque value, the final clamping forces can be as much as 30% lower than required. Essentially, tightening bolts in degrees of rotation largely eliminates the effects of friction between threads and the bearing surface between the head of the bolt and the bearing washer.