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Engine Building Fundamentals: Preparing Threaded Holes

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Preparing Threaded Holes

01.55

00:00 - While we're preparing the engine block, it's also a good practise to clean out all of the threaded holes in the block.
00:06 This is most important for the critical threaded holes for the likes of the head bolts or studs and main bearing cap fasteners; however, it's a good practise to clean all of the other threaded holes while you're at it.
00:19 This process ensures that any corrosion or debris is removed from the threads in the block, and can also be used to repair any damage to the threads.
00:30 All this adds up to reducing the potential friction between the threads and the block, and the threaded fastener you're going to instal.
00:38 This is essential to prevent damage to the fasteners, as well as ensuring you achieve consistent clamping force.
00:46 When we're dealing with the less critical threaded holes that we're likely to find on the engine block---perhaps those used to secure the sump to the sump rails, or perhaps even for items such as the engine mounts or external brackets---it's still valuable to clean these threads to ensure that your bolts are going to instal easily, and that you're not going to risk damaging the thread, damaging a bolt, or, worse still, having a fastener snap off in the block.
01:13 The process of preparing the threaded holes simply involves running a tap through the holes.
01:19 There are specific thread chasing taps available on the market that are designed for this specific purpose.
01:26 However, I've always used a general tap to do the job.
01:30 If you're cleaning out blind holes, then you're best to use what's known as a bottoming tap, or plug tap, which has less of a lead-in and will clean the threads all the way to the bottom of the hole.