In engine rebuild projects, making the decision between aftermarket head studs and original manufacturer head bolts is important. The choice you make will have a significant impact on automobile performance, so it's important to carefully research the issue.
Differences between head bolts and head studs
Choosing the right option requires machinists to understand the differences between how the two are attached on the engine assembly and how they function afterwards.
A head bolt will stretch out when it is initially installed on an engine assembly. Because it will be permanently altered by its first installation, it is meant to be installed only once. New head bolts must be put on when internal maintenance is necessary on the engine.
Original manufacturer head bolts will be subjected to both a clamping and twisting force at the when the engine is running. Being subjected to these two forces at the same time slightly detracts from the grip and the seal quality of the bolt. This makes a head bolt appropriate for the everyday use of a vehicle but inadequate for the heavy demands of high performance vehicles.
When a head stud is attached to the engine assembly, there is no clamping required in the machine shop. However, the head stud will stretch out in the vertical direction. The torque load on the head stud is evenly distributed over the head stud, and this will minimize the risk of gasket failure while the engine is in operation.
Head bolt cost effectiveness
Head bolts are sometimes chosen over head studs because they are made more cost effective through the use of a lower-grade steel. The tensile strength and class rating of a head bolt made from lower-grade steel will both be lower than the strength and rating of a head stud. Also, a head bolt will offer a weaker seal than a head bolt.
However, head bolts are adequate for engine rebuilds if the engine will be going in to a daily driver that will not be subject to the demands of high performance vehicles.
The tensile strength of an aftermarket performance head stud will stand up to greater demands. This type of head stud will typically be created through a cold forging process that allows for superior molecular integrity. Head studs are typically heat treated before they are hardened through a thread rolling and machining process.
If an engine is being rebuilt for a performance vehicle, a head stud with a high class rating and tensile strength is important. If you are working on an engine that will go in an everyday commuter vehicle, a good original manufacturer head bolt will be more than adequate.
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