Magazine for the auto service professional
Issue link: http://asp.epubxp.com/i/684411
50 | ASP June 2016 Technical on many annoying exhaust leaks, without a single failure. I apply a thin bead to both sides of a new exhaust gasket, or (depending on the engine application) apply a bead around all exhaust ports without the use of a mechanical gasket. Granted, the surfaces must be absolutely clean prior to application, but that's true for any sealing job, whether you're using a cut gasket, chemical or combination. Te high- temp copper RTV really does work on exhaust sealing surfaces. Sealing threaded connections Any threaded plug or connection that fea- tures tapered threads (such as NPT threads) requires a thread sealant. Typically, a Tefon or PTFE pipe sealant is a good choice. If a fuid plug or connection features straight threads, the ftting or plug requires a sealing washer and may require a thread sealant in addition. Depending on the specifc application, this may involve either a rubber O-ring or a soft-metal crush washer such as copper or aluminum. While it's common to sometimes require thread sealant on straight threads where a copper or aluminum crush washer is present, do not apply a thread sealer to a straight- thread ftting that uses a rubber O-ring. Also, if the ftting or plug features straight threads and a sealing washer, make sure that the surface that contacts the O-ring or crush washer is fat and clean, free of burrs or contaminants. If an O-ring seal is featured, lightly lube the O-ring with engine oil or transmission fuid, depending on the type of fuid to which the O-ring will be exposed. Always use a new copper or aluminum crush washer and O-ring (depending on the application). Securing threaded fasteners In addition to following torque (or torque- plus-angle) specifcations, certain fasteners may also require a "locking" feature, either mechanical or chemical. While a majority of bolts or nuts may specify the use of a lock washer, certain bolts that do not use a lock washer may require a drop of a chemical thread locker to prevent the bolt from loosening during operation due to vibration and/or thermal cycles. Chemical thread locking compounds are usually anaerobic, which means that they cure in the absence of air. Once the fastener is installed fully, the chemical begins to cure. When using thread sealant paste, it only needs to be as deep as the root of the threads. Dur- ing engagement the sealant will be pushed and squeezed to fll any thread voids. An example of OE replacement engine sensors (coolant at left; oil pressure at right). While a new crush washer alone will likely sufce, thread sealant provides not only additional sealing, but should ease future removal. A banjo-style ftting requires the use of a crush washer on both sides of the banjo. Always replace crush washers prior to reinstalling any banjo ftting.