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Engine Building Fundamentals: Studs VS Bolts

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Studs VS Bolts


00:00 - When it comes to selecting a fastener there are a variety of options available including bolts and nuts, bolts and studs.
00:09 When we consider two of the more critical aspects of the engine block assembly we have the fasteners used to clamp down the main bearing caps as well as the fasteners used to clamp down the cylinder head to the block.
00:22 In OE applications, these fasteners are most commonly going to be a bolt however it's normal when building a performance engine to replace bolts with after market stud kits.
00:34 Let's discuss the differences and advantages of studs over bolts.
00:39 Bolts are cheap to produce and are perfectly effective in engines that are not highly stressed and are not going to require regular assembly and disassembly.
00:49 From a performance standpoint though, bolts are less than ideal.
00:54 When we tighten a bolt we are actually twisting it and this means that the bolt is reacting to two separate forces.
01:02 It's being stretched as well as being twisted.
01:06 Studs on the other hand are installed into the threaded hole and then a washer and a nut are tightened down onto the stud.
01:14 This results in the stud only being stretched in the vertical axis.
01:19 No real twisting force is placed into the stud.
01:23 This provides improved and more uniform clamping force when compared to bolts.
01:28 Using a stud also prevents the situation where a bolt is used that is slightly too long for the application which can bottom out in the engine block before achieving the required clamping load.
01:42 Admittedly, this is unlikely to be an issue when using the OE fasteners of course.
01:48 Studs also offer an advantage when it comes to component installation as they can act as guide dowels for the mating part, and ensure positive location for a gasket.
02:00 For example, when installing a cylinder head the studs ensure that the head gasket is correctly located on the engine block and the studs offer a guide as the head is lowered into place ensuring correct alignment.
02:14 Lastly, with a performance engine it's common for the engine to be disassembled and reassembled more frequently than a stock, road going engine.
02:23 Each time a bolt is installed and removed it has the potential to degrade or damage the mating threads in the engine block.
02:31 Studs on the other hand can be left installed in the block and hence the thread in the block are less likely to be damaged.
02:39 With all of this in mind it's easy to see why studs are preferable over factory fitted bolts in a performance application.
02:47 The important points to understand from this module are that studs are generally a superior option for any performance engine project.