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Engine Building Fundamentals: Fastener Lubrication

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Fastener Lubrication

03.36

00:00 - Regardless what sort of fastener we're dealing with part of the tightening process is going to involve applying a specific torque value to the fastener.
00:09 This is the method we're using to achieve the desired amount of stretch in the fastener.
00:14 We need to consider what's happening as we apply torque to the fastener though.
00:19 Understandably, there's a significant amount of friction present between the threads of the fastener and the mating threads in the hole the fastener is installed in.
00:30 There's also friction between the underside of the head of the fastener and the material it's being tightened against.
00:37 In approximate numbers when we torque a fastener down 50% of the energy applied goes into overcoming the friction between the underside of the head of the fastener and the part we're clamping down.
00:49 40% goes into overcoming the friction between the threads and only 10% actually goes to producing tension in the fastener.
00:58 Let's also consider that the amount of friction presented by the threads will depend on the actual condition of the threads.
01:06 For example, if the threads are corroded or in poor condition, this will present a higher friction coefficient.
01:12 And for the same amount of torque applied to the fastener, less clamping force will be generated.
01:19 What we want to do is ensure that when we're tightening a fastener we're always achieving a consistent amount of tension in the fastener and that this amount of tension is the same as that specified by the manufacturer.
01:33 When I use the term consistency here, I'm meaning that each fastener in a set will achieve the same amount of clamping force for a given torque and that the clamping force will remain consistent each time an individual fastener is installed and torqued.
01:50 It should go without saying that these aims require that the threads in both the hole, as well as the fastener are clean, in good condition and not showing any sign of corrosion or damage.
02:03 Beyond this though, we'll normally need to use a lubricant on both the threads of the fastener, as well as the underside of the head of the fastener too.
02:13 The type of lubricant can have a large impact on the amount of clamping force we achieve for a given torque and for this reason, it's always essential to use the lubricant specified by the manufacturer.
02:25 The lubricant may be something as simple as clean engine oil and in fact, this is what you'll commonly be told to use when using OE fasteners and OE torquing procedures.
02:36 With after market performance fasteners though, it's typical to use a special molly-based lubricant that further reduces friction over what engine oil alone can achieve.
02:49 The key here is to ensure that we're using the recommended lubricant for the fasteners we're installing and that we're installing them to the recommended torque setting.
02:59 It's not going to be advisable for example, to use a molly-based lubricant on an OE fastener and then use the torque specifications listed by the manufacturer to suit a 30 weight motor oil as a lubricant.
03:13 So they key take aways here are to understand that lubricant is required to improve the repeatability and consistency of the clamping loads and ensure the clamping load is as specified by the manufacturer.