Magazine for the auto service professional
Issue link: http://asp.epubxp.com/i/684411
52 | ASP June 2016 Technical Be sure to use the specifc type of chemical thread locker for the application. In terms of locking strength, these range from "mild" to "severe." Using a high-strength thread locker that's designed for "permanent" securing of a severe-duty stud can pose difculties during future fastener removal, unless heat is applied to liquefy the compound. If in doubt, refer to the thread locker maker's application charts. When applying a thread locking compound, there's no need to drown the bolt. A single drop in the thread engagement area will sufce. Formed in place/bead gaskets Many gaskets today feature a metal core (usually aluminum) with a computer-printed sealing bead placed on each side. Te sealing beads generally consist of an elastomer or silicone material. Te metal core serves as a platform for the sealing beads, and aids in preventing over-tightening, since the metal core acts as a stopper layer. Although it may be tempting to re-use some of these gaskets when the removed gasket appears to be in good condition, it's always best to replace these gaskets due to the pos- sibility that the printed sealing bead material may have over-crushed. Examples of these applications include water pump gaskets, oil pan gaskets, etc. On engines that feature a camshaft retainer plate with a printed sealing bead on the engine block side, always replace these retaining plates, as the sealing bead may have been compromised during its installed period and may not provide adequate sealing if re-used. Rear main seals A rear main seal oil leak is something that every technician dreads, due to the labor required to access the seal. Today's rear main seals are typically a one-piece design. Depending on the specifc engine, the rear seal may be installed to the crankshaft rear fange during crankshaft installation, or the seal may be captive to a rear engine cover. When installing a rear main seal, it is criti- cal to pay attention to the seal orientation so that the angled sealing lip faces inboard. Citing the GM LS engine as but one example, the seal is installed to the rear engine cover, with the seal engaging the crankshaft fange during installation of the rear cover. A nylon guide ring is frst installed to the inside diameter of the seal. As the rear cover is installed, this guide ring keeps the Notice the pinhole in this engine block's cylinder? As a result of an initially thinwall casting aggra- vated by corrosion from the water jacket, coolant was spewing into the crankcase, contaminating engine oil, leading to total main, rod and cam bearing failure. Unfortunately for the technician and the owner, the problem wasn't discovered until the shop had already replaced bearings and had the cylinders re-honed. If the engine features a camshaft retaining plate that has an imprinted sealing bead, always replace the retaining plate during camshaft service, as the sealing bead is designed for one-time use. Some gaskets, such as this GM LS engine water pump gasket, feature an aluminum core with an imprinted sealing bead. While torque specifcation should always be followed, the aluminum core serves as a limiter to prevent over-tightening.