Finding and sealing leaks can be time-consuming and frustrating. Whether it is a fluid leak or an exhaust leak, taking the proper steps are necessary to do the job right. This article will give you tips and advice. However, there are two commandments that you must always follow when trying to seal a leak. Always know and follow the OEM’s specs, and always use the correct sealant AFTER THOROUGHLY READING THE INSTRUCTIONS! Sealant manufacturers sometimes change ingredients and usage procedures, so don’t “assume” that you know how to use the sealant.
Engine leaks are both annoying and potentially lead to engine damage and failure. In this brief article, we’ll discuss ways to obtain proper sealing of oil, coolant and engine vacuum, while also providing an overview of various gaskets and sealing materials.
Mating surface condition
When cleaning mating surfaces prior to the installation of new gaskets, avoid the use of any hard metal scraper which can gouge or scratch the surfaces. This is especially true when dealing with aluminum surfaces such as cylinder heads, timing covers, oil pans, water pumps, etc. Aluminum alloy used on production engines is relatively soft and can easily be damaged with the careless use of a steel scraper.
Heavy scratches, nicks, burrs or gouges can create fluid escape paths, even when assembled with the highest quality gaskets.
Also, in order to avoid uneven or wavy surfaces, avoid the use of abrasives driven by a power tool, such as a die grinder or drill fitted with sandpaper or Scotchbrite pads.
Even though the surface may appear shiny and clean, unpredictable control of a hand-held power tool can easily create an uneven and wavy surface that will prevent a perfectly parallel surface-to-surface sealing.
Pay attention to OE specs
Depending on the design of a particular engine, the use of a gasket or rubber/synthetic seal may or may not be required for certain component areas.
If the mounting of a component was designed to use a form-in-place sealant instead of a pre-formed gasket, the use of a gasket, due to the gasket thickness, can result in misalignment of one component to another, positioning a component further way from its mating area. This can result in bolt hole misalignment as well as leaks.
By the same token, a component which was designed to use a gasket may or may not seat properly if RTV or another liquid or gel sealant is applied instead of a formed gasket.
There are many instances where a liquid or gel sealant may be successfully used in place of a cut gasket, as long as the final torque value and clamping load doesn’t move the component too close to the opposite mating surface. Cut/pre-formed gaskets not only provide sealing between mating surfaces, but also provide a specific spacing between the mating surfaces.
In other words, the type of sealing product can influence dimensional characteristics. This spacing distance from one component to another can either offer a degree of latitude, or it can be critical, depending on the specific application.
As an extreme example, let’s consider the camshaft caps on an overhead-cam engine that might require no sealant or a “packing” sealant liquid between the caps and cylinder head. If a mechanical gasket was placed between the caps and head, this would raise the caps up, creating an out-of-round and excessive oil gap between the camshaft’s journals and cam bores.
Our point is that not all mating surface areas require a mechanical gasket. When in doubt, refer to the vehicle’s service manual.
Sealing problem areas
When installing formed bead-type gaskets, as found on many late model valve covers, thermostat housings, and O-ring style intake manifold seals, consider applying a light coat of lubricant such as Vaseline or white lithium grease. This will aid in both holding the gasket in place during installation and will allow the material to slide and more easily conform into place during component installation, reducing the chance of tearing or mis-locating the gasket.
Before installing bead style or O-ring style gaskets into retaining grooves, take the time to make sure that the retention groove is absolutely clean and free of dirt particles or other obstructions that will hinder proper seating.
Pay attention to areas where corners and intersecting mating surfaces are involved. An example is where each side of a timing cover meets both the block and oil pan. In addition to the appropriate gaskets, a very small dab of RTV in these intersecting areas can aid in preventing an oil leak.
We’ve all run into problem sealing areas that result from damaged mating surfaces, where a cam cover, timing cover, etc., may have been distorted, nicked or gouged.
While the ideal cure would be to replace the damaged component, time and budget factors might prevent replacement. When an excessive gap is the source of a leak, a quick and inexpensive solution might be to apply a bead of sealant in that problem area.
I’ve used high quality RTV sealants to address many such issues. Choosing a specific sealant of course depends on the specific application, in terms of location, anticipated operating temperature and pressure and the type of gas or liquid involved. Leading chemical sealant makers offer a wide range of chemical sealants, each designed for a specific type of application.
Instead of grabbing just any tube of sealant, do yourself a favor and refer to the maker’s application information to select the sealant that is most appropriate for the job at hand. The application charts are worth the time it takes to read them, and will aid you in choosing precisely the correct chemical for the job.
It’s important to understand that not all RTVs, thread lockers, gasket makers and sealants are equal. A wide range of these chemicals have been developed to address very specific types of applications.
I can’t stress this enough — visit the brand’s website and look at the application charts!
An exhaust gas leak between an exhaust manifold and cylinder head, or between the exhaust manifold’s outlet to a pipe, can result from uneven mating surfaces (warped exhaust deck caused by previous uneven tightening). It also can cause small cracks or porosity in the exhaust manifold or corrosion at the mating surfaces.
While resurfacing or replacing the offending components may be ideal, budget and time doesn’t always allow the ideal. A high temperature RTV sealant that contains copper is often successfully used to remedy these small leaks. As an example, I’ve used Permatex high temperature Ultra Copper 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. The high-temp copper RTV really does work on exhaust sealing surfaces.
Sealing threaded connections
Any threaded plug or connection that features tapered threads (such as NPT threads) requires a thread sealant. Typically, a Teflon or PTFE pipe sealant is a good choice.
If a fluid plug or connection features straight threads, the fitting or plug requires a sealing washer and may require a thread sealant in addition.
Depending on the specific 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 fitting that uses a rubber O-ring.
Also, if the fitting or plug features straight threads and a sealing washer, make sure that the surface that contacts the O-ring or crush washer is flat and clean, free of burrs or contaminants.
If an O-ring seal is featured, lightly lube the O-ring with engine oil or transmission fluid, depending on the type of fluid 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) specifications, 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.
Be sure to use the specific 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 difficulties 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 suffice.
Formed in place/bead gaskets
Many gaskets today feature a metal core (usually aluminum) with a computer-printed sealing bead placed on each side. The sealing beads generally consist of an elastomer or silicone material. The 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 possibility 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 specific engine, the rear seal may be installed to the crankshaft rear flange during crankshaft installation, or the seal may be captive to a rear engine cover.
When installing a rear main seal, it is critical 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 flange during installation of the rear cover. A nylon guide ring is first installed to the inside diameter of the seal. As the rear cover is installed, this guide ring keeps the inboard seal lip facing forward. When the cover is fully installed, the guide ring pops off.
When installing this type of seal, the seal should be installed dry. Do not lubricate the seal lips prior to installation to the crankshaft. After the rear cover is in place, flush against the block, closely inspect the seal to verify that the lip has not been pulled rearward. If it has, remove the cover, reinstall the nylon guide ring and re-install.
Cylinder head gaskets
The subject of cylinder head gaskets deserves an entire, lengthy article devoted to this very complex area of engine sealing. Cylinder head-to-block sealing requires a combination of properly prepared deck surfaces, the correct type of gasket, and the correct clamping force.
Internal leakage can allow coolant to enter the combustion chambers and oil passages. If coolant enters the combustion chambers, not only will the engine consume coolant, but any coolant in the chambers will turn to steam, increasing chamber pressure, and eventually damaging pistons and valves.
Coolant entering oil will degrade the oil’s ability to lubricate.
While applications for composite head gaskets continue to exist, the majority of production and performance engines now use MLS (multi-layer steel) gaskets.
MLS head gaskets
MLS cylinder head gaskets have been employed by OEMs since about 1991 (with Ford and Mitsubishi) and are commonplace in OE engines today.
Unlike a composite gasket, MLS gaskets are constructed of multiple layers of hardened stainless steel, featuring embossed outer “active” layers and “passive” or “stopper” inner layers. The embossed layers are raised areas that provide sealing, with the stopper layers providing both a dead-stop during clamping (which prevents over-compression), as well as the desired gasket thickness.
The assembly, which may feature three to five layers depending on the application, is secured together with rivets. The embossed active layers compress and expand during engine operation as the cylinder head tries to lift off of the deck during combustion, essentially acting as tensiled springs to maintain constant sealing contact between the head and block deck.
Bill McKnight, MAHLE – Clevite and Victor aftermarket training manager, offers a way to visualize the task of the head gasket.
“What happens as an engine runs is that the cylinder head is actually lifted off the block from the firing pressure in the cylinder,” he says. “It’s hard to imagine this, but the head bolts are elastic and stretch a bit to allow this head lift-off.
“The MLS gasket actually acts as a spring, relaxing, then being compressed again every time the cylinder fires. If you drove your car at 70 miles an hour for 200,000 miles and it ran a steady 2,400 rpm, the cylinders would each fire 201,600,000 times.
“The math is simple: 2,400 rpm means each cylinder fires 1,200 times a minute (two revs of the crank for each firing) times 60 minutes per hour is 72,000 times in an hour. At 70 mph it would take 2,800 hours to drive 200,000 miles. So, 2,800 hours, times 72,000 times per hour, is 201,600,000 times! This means, of course, we have compressed then relaxed the head gasket material 201,600,000 times!”
Since a bare stainless steel gasket surface would have a difficult time in sealing against even the finest machined surface, a specialized coating is applied to the outer surfaces that aids in filling microscopic voids in the deck surface finishes.
As Fel-Pro Product Manager Ron Rotunno points out, in the early days of MLS head gaskets, the seal coating was somewhat sticky, which prompted handling cautions, advising installers not to remove gaskets from their packaging until immediately prior to installation.
“The concern was that contaminants such as airborne particles or transfer from dirty fingers, etc., would stick to the surfaces, possibly preventing an ideal sealing surface,” says Rotunno. The coatings used today by leading makers of MLS head gaskets do not feature a super-sticky rubber, so it’s OK to expose the gaskets to the air at any time.
According to Rotunno and McKnight, today’s coatings, depending on the specific application, may consist of advanced polymers and/or FKM Viton. While early generations of coatings demanded an extremely fine surface finish, today’s coatings are capable of sealing even on less-than-ideal surfaces, allowing compatibility with slightly rougher Ra finishes.
Cylinder block deck and head deck surface finishes are commonly graded on a roughness-average (Ra) scale, with a lower Ra indicating smoother and a higher Ra as less-smooth. For instance, an Ra 5 would indicate an extremely smooth, almost mirror-like finish, while an Ra of 100 would indicate a rougher machined surface.
Today’s advanced MLS gaskets are more forgiving, capable of sealing Ra finishes even in the 30 to 70 Ra finish. This allows repair shops to install heads with less than ideal surface finishes.
However, regardless of today’s gasket technology, even the best Ra finish won’t allow proper sealing if the surface is deeply scratched or gouged. So, while cleanliness and attention to surface finish remains critical, the average repair shop will be able to restore cylinder head sealing in real-world situations, without the need to meet extremely fine surface finishes.
According to Rotunno, a typical OE finish today calls for an Ra of 30, but the coatings today can easily handle a range up to 50 Ra and sometimes higher.
When installing an MLS head gasket, make sure that all surfaces are clean and dry. Do not apply any type of additional sealant. A high-tack or copper sealant can dry too quickly and result in uneven thickness, and can become trapped between MLS layers.
In short, always install an MLS gasket dry.
Cylinder head bolts (or studs) are absolutely vital in achieving proper cylinder head installation. Even with the highest quality head gaskets and ideal deck surfaces, head gasket failures can occur if clamping loads are not at the correct value. Female threaded holes, bolt threads, thread lubrication and proper clamping loads are all critical factors, and are far too often overlooked during head installations.
Clean the threaded holes in the block deck to remove any contaminants and thread deformation. Use a chaser tap to clean female threads.
Unlike a common cutting tap, a chaser tap is designed to clean and restore existing threads without removing material. Use a solvent and wire rifle brush to clean threads, followed by blowing with compressed air. Chaser taps are readily available through any decent tool supplier.
Also, if the block deck has been resurfaced, make sure that the top of all female bolt holes are slightly chamfered to remove a sharp, and possibly raised, edge which could potentially be drawn upwards above the deck mating surface.
The tensile strength and elasticity of head bolts is extremely important, since the bolts, when properly tightened, are designed to stretch and provide clamping force. The bolts don’t just sit there. They are exposed to dynamic forces as the head tries to pull away from the block during engine operation. This requires the bolts to be somewhat elastic as they are tightened, but if tightened too far, they will stretch beyond the elastic range into a yield, at which point they lose their ability to clamp.
Many production engines today feature TTY (torque-to-yield) bolts that are designed for one-time use. TTY bolts should never be re-used. Even if you are unsure if the bolts are TTY, it’s always best to replace all cylinder head bolts whenever installing a head. Re-using an unknown-quality bolt is simply not worth the risk. Entire articles can easily be devoted to the subject of cylinder head bolts.
Once all bolts are clean, lubricate the bolt threads, the bolt head underside, and each side of the bolt washers with an appropriate lubricant. Be aware that any tightening specs are based on a certain type of lubricant. Commonly used bolt lubricants include engine oil, a moly-based lube or other high-pressure lubricant such as CMD.
If using OE bolts and following OE tightening specs, use the lube specified by the OE (which will commonly call for engine oil).
If you are using aftermarket bolts, follow the recommendation of the bolt maker. Some aftermarket bolt makers may give you a choice between oil or moly, with torque values appropriate for each.
Certain moly-type lubes provide greatly reduced friction as compared to oil, a torque value with moly will commonly be lower than the value recommended when using oil.
Follow the bolt tightening procedure specified by either the OE or the aftermarket head bolt manufacturer, which may specify a torque value or a torque-plus-angle method.
If torque-plus-angle is specified, you can apply initial torque with a calibrated torque wrench.
You can follow this with additional angle-turning by applying a paint dot on the bolt head and visually monitoring (and guessing) the number of degrees of added rotation.
Or a much easier and quicker method is to invest in an electronic torque wrench that also offers angle tightening (enter torque mode, apply torque; enter angle mode and apply angle). ■
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