Engine sealing tips: How to avoid problems from annoying leaks to devastating damage
Posted on February 11, 2015
by Mike Mavrigian
- Also by this author
While gaskets and formed seals apply to the majority of engine sealing issues, there are instances where an additional sealing compound is required, such as where component corners meet, creating a potential gap, or where a metal-to-metal joint must be addressed. Also, when dealing with a less-than-ideal mating area (such as a distorted oil pan or corroded valve cover lip, etc.), an additional sealing compound may be needed to ensure against leakage. In addition, there are applications wherein the OE specification calls for the use of a packing material instead of a cut or formed gasket (packing material is a term often used by OEMs to refer to sealing compounds such as RTV).
Speaking in very broad terms, there are two basic families of sealing compounds — anaerobic and RTV. An anaerobic sealant is designed to cure in the absence of air (an example is a thread locking compound that cures once the bolt/nut is fully tightened). An RTV (room temperature vulcanizing) sealant cures by exposure to air. Depending on the specific application, an array of dedicated compounds are available to address a wide range of sealing requirements, based on anticipated temperatures, vibration resistance and exposure to different fluids, such as coolant, engine oil, transmission fluid, fuel, etc. Excellent sources of reference include such brands as Permatex, Valco and others, where detailed information regarding the proper selection of sealant is readily available. When a sealing compound is required, don’t just grab any tube of RTV that might be handy. Be sure to use the correct type for the specific application. ●
Improperly tightened cylinder head fasteners can easily lead to head gasket failure. Always follow the engine maker’s specifications for torque value as well as the tightening pattern/sequence. Incorrect tightening patterns can result in uneven stresses that lead to cylinder head warpage.
The subject of engine sealing deserves to be discussed at great length. Given the limited space provided in this article, we’ve addressed a few common areas. Always refer to the appropriate service manual for the specific engine at hand. Following the proper assembly techniques for a specific engine will avoid leakage complaint comebacks.
Never install a cylinder head without the use of a quality torque wrench. Regardless of the style of wrench (beam, ratcheting, dial or digital), your torque wrenches should be checked for calibration at least on an annual basis.
For today’s engines that require a torque-plus-angle cylinder head tightening procedure, a digital torque/angle torque wrench provides a quick and accurate method, eliminating the need to switch to an angle gauge. Place the wrench in torque mode, select ft-lb or Nm, select the value, and tighten. Then switch to the angle mode, set the desired angle and continue to tighten.
Engine covers (such as the LS front cover shown here) often feature a metal-core gasket that features a pre-applied sealing bead. No additional sealant should be required.
Some components, such as the camshaft retainer plate for the LS engine, feature a printed seal that has been directly applied to the metal plate. This type of seal is not a serviceable piece. In order to ensure proper sealing, replace the plate with a new one.
In addition to applying lubricant to the bolt threads, always apply lube to the underside of the bolt heads or nuts, where studs are featured. This reduces the friction at all contact points during fastener tightening, for more accurate torque application.
In those applications where cylinder head studs are to be used (instead of bolts), it is only necessary to install the studs finger-tight. The clamping force will be applied as the nuts are tightened. Never double-nut a head stud to tighten the stud to the block.
Any tapered thread plug requires a thread sealant, such as a Teflon paste. Try to avoid the use of Teflon tape, as loose tape strings/fragments can potentially break loose and contaminate the engine.
Many of today’s rocker covers feature grooves that accept formed silicone/elastomer bead seals. These seals are easily replaced, and usually feature a “barbed” cross section design that sufficiently locks the seal in place to the groove.
Formed gasket bead seals are commonly used in late model engines. Always install a new seal, even if the original appears to be OK.
Pay attention to rocker arm bolt holes, as some holes may be open to the intake runners. The GM LS engine for example, features open intake rocker arm bolt holes. To prevent vacuum leaks, apply a thread sealer to the intake rocker bolt threads.
Today’s RTV sealants are available in a range of dedicated formulations for specific applications, in terms of heat, vibration, gap coverage and oil resistance.
Intake manifold gaskets may feature composite construction, a hard plastic substrate with sealing beads, or individual sealing bead seals. Some intake gaskets that feature a hard plastic core may feature locating tangs that engage into the heads. Since OE engine makers have used various designs over the years, make absolutely sure that you order the correct gaskets for the engine model and year.
Applications that call for a chemical seal, or when a cut gasket is not available, high performance RTV sealants provide a suitable seal. Avoid excess application to prevent sealant from entering ports, and pay attention when selecting the correct type of sealant for any given application.