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Practical Engine Building: Sealants and Threadlockers

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Sealants and Threadlockers

08.43

00:00 - During the assembly process of any engine, you're going to need to use silicon sealants or liquid gasket to seal various engine components, thread sealants to seal some threaded fittings, as well as threadlocking compounds on some of the more critical fasteners used in the engine.
00:18 Most people who have had some exposure to general automotive maintenance tasks would be aware of these sorts of products already, however there are actually quite a wide range of products in this market and not all are suitable for every task.
00:33 Using the wrong product can waste time and money when the freshly assembled engine develops an oil leak for example.
00:40 We'll start by discussing sealants which are often called for by manufacturers to seal components in favour of a conventional gasket.
00:49 Components where you're likely to use this sort of product may include the sump where it seals to the sump rails of the block, the rear main seal housing where this bolts to the block, and the front cover where this bolts to the front of the block.
01:04 One of the advantages of using a flexible sealant is that it's very good at filling voids or imperfections in the mating surfaces and hence preventing leaks.
01:14 When it comes to choosing a suitable product, there are a huge variety on the market and not all are suitable for our requirements.
01:23 In particular we need a sealant that's designed to withstand the heat the it will be subjected to on a running engine.
01:30 And it also needs to be resistant to chemicals such as oil and fuel.
01:35 This isn't a difficult task, and most automotive parts retailers will be able to supply sealants that are specifically designed for making gaskets like this.
01:45 Often the OE manufacturer will call for a specific product in the workshop manual and understandably you can't go wrong if you choose to take their advice.
01:56 One of my pet hates is where a freshly built engine's completed with thousands of dollars worth of aftermarket components installed inside, along with the required machine work and hours of assembly, only to have the sump and associated parts sealed up using orange silicon that's designed for sealing exhaust systems.
02:16 Typically this orange sealant will also have been applied in vast quantities leaving unsightly globs of the stuff smeared all over the freshly built engine.
02:26 While this may well get the job done, in my opinion it looks terrible, and particularly if you're assembling an engine for a customer, this is probably all they're going to be able to see of your workmanship, so you're going to be judged on this, regardless how accurately the engine is assembled.
02:44 When I'm assembling an engine I prefer to use an OE grade silicon such as those supplied by ThreeBond.
02:51 This does an excellent job, and also offers a professional OE appearance.
02:57 Since sealing components with these products is an area that a lot of people struggle with, we deal with the correct technique in a specific module in the Practical Engine Building Skills Section of the course.
03:10 Next we'll consider thread sealants which is another area that many novice engine builders go wrong.
03:17 These products are often required on both oil and water fittings on the engine block and cylinder head, however there's a few aspects that need to be understood.
03:28 Firstly there are two types of fitting that we may need to seal.
03:32 Straight and tapered threads, and both of these require different techniques and different products.
03:39 Let's start by discussing those terms, straight and tapered threads.
03:44 As their name implies it refers to the shape of the threads on the fitting, and they may either be straight, where the threads are parallel to each other, or in other words the same diameter from one end of the fitting to the other, or tapered where the end of the thread is smaller in diameter to the base of the thread.
04:04 A straight threaded fitting doesn't seal against the threads itself and instead will require a sealing washer or similar that will sandwich between the back of the fitting and a flat surface on the block.
04:17 A good example of this type of fitting would be a banjo bolt fitting that's bolted to the engine block to supply oil or potentially water to a turbo charger.
04:27 The banjo bolt requires a copper or alloy washer on each side of the banjo fitting to do the sealing work.
04:35 Applying a thread sealant to this type of fitting won't do anything to help seal the fitting, and it can actually be detrimental as it may end up making its way into the turbo charger and causing damage.
04:49 The other type of fitting where the thread is tapered relies on the interference between the threaded fitting and the matching thread in the cylinder head or block to do the sealing.
05:00 As we wind one of these fittings into the mating thread, it will gradually become tight, and it should never bottom out.
05:07 The threads themselves however are not enough to seal against the oil or water, and this is where a small amount of thread sealant is required.
05:17 The workshop manual will clearly tell you what fittings require thread sealants if you're not 100% sure.
05:24 Thread sealants can broadly be separated into thread sealing tapes and liquid compounds.
05:30 While either can get good results, I personally prefer a liquid sealant such as Loctite 567, which is easy to apply and easy to achieve professional looking results and a reliable seal.
05:43 Thread sealing tape on the other hand, does require a little bit more care in order to achieve a good and reliable seal.
05:50 Lastly we'll discuss threadlocking compounds, which can be used to prevent a fastener from loosening, due to the vibration and heat it's subjected to.
06:00 These are generally either a liquid that's lightly applied to the threads of a fastener before installation, or in some instances a semi solid stick that can be rubbed across the threads.
06:12 There isn't one single threadlocking compound either, and the correct product will depend on what we're trying to achieve.
06:20 For example there are products designed for very high strength for semi permanent installation, and lower strength products that provide good thread locking properties, but still allow the part to be disassembled without too much difficulty.
06:35 There are also products that are designed to wick into the threads of parts that are already assembled.
06:41 For most of the critical fasteners on the engine, I tend to use the Loctite 243 product, which is a medium strength fast cure thread locker.
06:50 To help you decide on the correct product for your application, you'll find a handy product selection flow chart from Loctite attached to this module.
06:59 I should also mention that this is not a paid advertisement for Loctite, however I use this product, as it's a well known internationally respected brand.
07:09 Of course you're free to use your own preferred threadlocking compound.
07:13 If you're using a thread locking product, it's important to make sure that the threads on the fastener and also the matching threads in the component you're fitting it to, are clean and free from oil.
07:25 This can be achieved easily using brake clean and compressed air.
07:30 When it comes to applying a threadlocker product to fasteners such as fly wheel bolts, often I see mechanics apply a liberal coat of thread locker to the threads of the flywheel bolts before starting them in the end of the crankshaft by hand and then tightening them with an impact driver.
07:49 This actually has the affect of spraying the threadlocker product out from the bolt, as it's rotated at high speed by the impact driver.
07:58 The threadlocker product that's sprayed out from the bolt, can actually end up between the components you're trying to clamp, such as the flywheel and the crankshaft flange.
08:08 This can be detrimental to the reliability of the clamp joint and it's a better option to wind the bolt in by hand or with a ratchet, until you're ready to torque it to specification.
08:20 On this note we also need to understand that the threadlocker has a finite amount of time before it will set so we want to install the components and torque them quickly before the product does set.