There are few things that can ruin a repair or restoration job faster than a fluid leak. As an example, a muscle car that is painstakingly restored can be marred by an unnecessary repair such as having to remove the engine to eliminate an oil leak. This exposes the vehicle to being scratched or dented and, no matter how great a mechanic you are, it never goes back together the exact same way. There will always be small signs of the surgery, such as wrench marks on bolt heads or the need to touch up some engine or under-hood paint work. Others may not be able to see these telltale indicators of a job gone bad, but trust me–every time you open the hood, your eye will go right to that area as if it were lit in neon.
Anyone who has been around machinery as long as I have knows that it is impossible to guarantee that a component will never leak after being installed, but employing the proper procedures goes a long way toward pushing the odds in your favor.
To many enthusiasts, the science of sealing is often neglected and little care is given to addressing this potential problem area. It is falsely believed that you can be slipshod with your mechanical procedure and the gasket or sealant will make up for all sins. In many cases this is true, but don’t bet the farm on it.
Oil leaks are especially bothersome for a host of reasons. First, they often are a major job to eliminate, requiring work on a rear main seal or oil pan. In addition, the escaped lubricant from almost every oil leak will work its way to the bottom of the engine, where it will then be blown around the chassis of the car when driven, leading to the other issues that arise from leaked oil. Leaked oil attracts dust and dirt, does not evaporate, and leaves a calling card everywhere the vehicle is parked. It is very embarrassing to have a beautiful car leave drips on the pavement after you drive away.
Though oil is the predominant leak that will need to be dealt with, there are other fluids in the vehicle that can be just as anxious to escape from their proper place. Transmission, power steering and brake fluid, differential grease, coolant and gasoline can all prove to be just as stubborn to control.
Understanding gaskets
A gasket is described as a seal that is used between two parts to create a leak-free environment. A cylinder-head gasket is the most complex found on an engine, since it needs to stop coolant and combustion leaks. A gasket may appear to be simple, but in reality, there are many design considerations and material choices. The following are properties of a gasket:
Conformability: Gasket surfaces must be able to conform to slight surface imperfections. This includes warpage, corrosion, erosion and roughness from machining.
Creep relaxation: As a gasket is continually stressed, its interporosity undergoes a collapse change over a period of time. This leads to a lowering of the bolting force and flange pressure. If flange pressure falls below its critical value, the gasket will fail and the component will leak.
Impermeability: A gasket must not permit passage of the medium it is designed to seal in.
Elasticity: This property allows the gasket to maintain sealing pressure regardless of normal vibration or temperature change.
Wear resistance: For longterm performance, a gasket must resist the conditions of age, fluid attack, pressure and heat.
Many different materials are employed for gaskets and, over the years, new substances have been brought to market. When dealing with an older vehicle, it is very possible that the replacement gasket will be of a completely different composition than the one fitted at the factory. A good example of this is the substitution of neoprene instead of graphite-impregnated rope for a rear main oil seal. Common automotive gasket materials are:
Cork: Pure cork is the inner bark of the Mediterranean live oak tree. For gaskets, granules of this cork are held together with binders that are either phenolic resins or latex. It is the binder that gives cork gaskets certain undesirable characteristics.
Gaskets made of cork have several disadvantages. The shelf life of cork gaskets is relatively short, since they lose moisture, shrink and become brittle. They also have a tendency to “wick.” This is caused by capillary action pulling oil through the voids between the cork granules.
For this reason, many hobbyists who see dirt and oil film on the outside of an oil pan or valve cover with a cork gasket believe that it is leaking, and consequently over-tighten the hold-down bolts. This will not stop the natural wicking process that is responsible for the dirt accumulation. It only distorts the sheetmetal of the part and creates a leak.
Automotive cork gaskets do offer some advantages over other materials. They are easily installed on wet or dry surfaces, due to their high coefficient of friction. The cork product also has excellent compressibility and possesses good torque retention.
Cork is used in applications where oil is to be contained, where bolt loading is low, and where there are no pressure and temperature extremes.
Rubber: This material is more expensive than cork, but has unlimited shelf life and no wicking problem. Heat resistance is also excellent.
Rubber gaskets have the shortcoming of displacing (pushing out) under pressure rather than compressing. Industry have shown this displacement can result in a 50 percent loss of flange pressure after 500 to 1,000 hours of engine operation.
The installation of rubber gaskets is often a problem. For example, you have probably had a rubber rocker-cover gasket squirt out of position as torque is applied. This occurs because oil-dampened rubber has almost zero coefficient of friction. The key to a successful installation is making sure that the mating surfaces are absolutely clean and dry. Some like to use special adhesives to keep the gasket in place.
Cork/rubber: This type of gasket material is cork with rubber used as the binder. It provides all the good features of both cork and rubber gaskets with none of the bad qualities of either.
Paper: These gaskets are designed for use in low-pressure, low-temperature environments. Paper gaskets usually are treated to resist oil, coolant and gasoline. The mounting gasket for a mechanical fuel pump is an example of a paper application.
Fiber: Cellulose, asbestos or a combination of the two materials often is used in high-pressure, high-temperature areas. The fiber may be bonded to a steel core.
Room-temperature vulcanizing silicone rubber (RTV): This material is commonly used for formed-in-place gaskets. RTV usually comes in a tube and is applied as a paste. The curing agent for this material is the humidity in the air. After curing, the material has tough, rubber-like characteristics and has temperature resistance to 450 degrees F. Formed-in-place silicone gasket material works especially well around water passages or where there are uneven clamping pressures.
Anaerobic materials: These formed-in-place compounds cure in a manner opposite to RTV. Anaerobic materials cure when confined between metal parts–anaerobic means “life in absence of air.” Originally, Loctite Corporation developed anaerobic materials as a way to secure threaded fasteners (Loctite). Later, the materials were made suitable for formed-in-place gaskets. After curing, the gasket is a tough polymerized plastic that has 400 degrees F temperature resistance.
Head gaskets
The job of sealing the cylinder head to the block is extremely difficult. Coolant, lubricating oil and combustion pressures must simultaneously be contained. If that were not tough enough, a head gasket must be able to perform through a wide temperature range. The seal area may be well below zero degrees on a cold morning, but when the engine is started, the temperature quickly shoots to over 400 degrees. There are several popular designs for head gaskets:
Metal sandwich: This style uses a face of copper or steel over an asbestos core. Always handle sandwich gaskets with care. Avoid distorting or bending. Store the gasket in a flat position and never on the edge. Do not attempt to straighten a bent sandwich gasket, as failure will result.
Embossed steel: This gasket is sometimes called a shim style and was commonly used by Detroit. The raised or embossed area is what gives it the required resiliency. The steel is usually around 0.030-inch thick and coated with aluminum or tin. Under heat, the coating flows into the parting surface machine marks and provides additional sealing.
Soft surface: Many aftermarket head gaskets are this style. The gaskets have a treated asbestos facing attached to both sides of a perforated steel core. A stainless steel fire ring is wrapped around the cylinder opening to seal the combustion chambers.
These gaskets are slightly thicker than the embossed steel style, to help compensate for casting resurfacing. Also, these gaskets are less susceptible to liquid leaks than metal face styles.
A few years back, a trend started toward the use of “no re-torque” head gaskets. This saves the cost, inconvenience and time of re-torquing the cylinder head after break-in. No re-torque head gaskets combine the compressibility of the metal sandwich style with the torque-retaining ability of the embossed steel shim.
Cylinder-head torque retention is directly related to the amount of head-bolt stretch and the compressibility of the head-gasket material. It then becomes the job of the gasket engineer to control creep relaxation and retain the desired “clamp-up” torque when designing a no re-torque head gasket.
Manifold gaskets
There are three specific kinds of manifolds in use on engines: the intake, the exhaust and the combined (used with an in-line engine). Different materials are employed for each.
Intake manifold gaskets must have the ability to seal vacuum, fuel vapor and coolant pressure at the crossover. To provide the necessary rigidity and prevent wall collapse, several designs are used.
One popular style is a solid steel core with chemically bonded soft fiber faces. Some are covered with a blue Teflon coating to provide stick resistance and eliminate the need for gasket sealer.
Certain V-8 engines use a one-piece metal pan with both sides cut and embossed to mate with the intake manifold. This design also serves as a deflector plate to prevent oil splash from caking on the bottom of the exhaust crossover on older engines.
Many American engines were built and designed without exhaust manifold gaskets. These depend on casting-to-casting fit for the seal. However, repeated heating and cooling cycles often distort the exhaust manifold, and a gasket becomes necessary as the engine gets older. The most common type has a perforated steel core with asbestos attached to each side.
The combined-type manifold gasket is used on many in-line engines and, for best sealing characteristics, often makes use of different materials at the intake versus exhaust ports.
Oil seals
Oil seals are used throughout the engine and may be either a lip-style, such as the front seal in the timing cover, an O-ring, or a rope/neoprene design.
Oil seals are classified as either static or dynamic. A static seal is used between two stationary parts. Front and rear oil-pan end-seals are an example of static seals. Dynamic seals are used between a stationary and a moving part. The timing cover crankshaft seal and the rear main bearing seal are examples of dynamic seals.
Eliminating leaks
If the component in question leaks, and it is not damaged or warped, then you did something wrong. Successfully sealing an engine is not hard, but requires that the proper mechanical procedure be followed; this is not a place for shortcuts.
The first step in correcting a leak is to purchase the proper gasket–not a “one-size-fits-all” style that the auto parts counter person tries to convince you will work. The next step is to only buy name-brand, high-quality gaskets. If you have been in this hobby for more than a week, you know and recognize what the brands are. Resist the temptation to save a few bucks and buy a cheap gasket that may fit the part properly but is made from inferior or incorrect material. There is a reason why name-brand gaskets cost more.
Surface preparation, which is often the most tedious and time-consuming of jobs, is paramount to a leak-free seal. Even the best gasket cannot work if the surface is not prepared properly. My edict, when it comes to surface preparation, is to make it “surgically clean.” I spend a lot of time cleaning and inspecting any gasket surface. In over 30 years of working on cars and machinery, I never had an installation leak due to my workmanship. So many mechanics never have the time to do it right the first time, but always manage to find the time to redo the job when it leaks. Another aspect of surface preparation beyond cleanliness is the shape. This is especially important when sealing sheetmetal engine parts, such as the oil pan, or timing, rocker and differential covers.
The last step is a proper tightening sequence with clean fasteners and bolt holes. A part should be brought to final torque in stages and the sequence should always be in a criss-cross fashion. A sure sign of a poor or inexperienced mechanic is one who does not follow the proper tightening steps and, instead, rams each fastener “home.”
Since many of these procedures are best shown with pictures, HMM worked with Mark Erney, shop manager at Jim Taylor Engine Service in Phillipsburg, New Jersey, to illustrate how to eliminate leaks.
PHOTO 1
A new gasket should always be used when a repair is performed. Always trial-fit the gasket to the part to confirm that it is correct, but also to help determine if the component is warped and the thickness of the gasket is sufficient to compensate. With a hard-to-find part, it may be necessary to double up a gasket to compensate for warpage if it cannot be corrected.
PHOTO 2
Every mechanic should have a dedicated gasket-scraping tool. Though many like to use abrasive pads on an electric or air drill, if you’re not careful, material can be removed, ruining the component. Gasket removal is just that–it is not meant to remove metal.
PHOTO 3
A wire wheel should be used to clean the bolt threads so proper torque can be applied. Dirt in the threads will make the bolt seem tight but will not apply the required clamping force to the gasket.
PHOTO 4
In similar fashion, all bolt holes should be chased with a tap to remove any dirt, debris or corrosion.
PHOTO 5A & 5B
Brake cleaner works excellently as a gasket-surface cleaning agent. It degreases and leaves no residue. When replacing cylinder-head gaskets without the engine being machined, a single-edge razor blade should be used to clean the surface; these are gentle enough to not mar the finish. The proper finish is required for the head gasket to seal properly.
PHOTO 6
A wire wheel is an efficient way to remove old gasket material from sheetmetal parts. It should not be used on any part attached to the engine, as the debris will enter the engine.
PHOTO 7
There are many different methods for straightening a sheetmetal part’s gasket flange. Here, the bolt holes are being peened flat after years of over-tightening. The part should be checked on a flat surface and “tweaked” with a piece of wood and a hammer to be made straight.
PHOTO 8
When installing or checking a sheetmetal part with a gasket, such as a rocker cover, a ¼-inch drive ratchet is the only tool you need. A small ratchet will inherently limit the amount of torque applied to the fastener and will decrease distortion of the sheetmetal.
PHOTO 9
Thermostat housings are very prone to coolant leaks due to poor surface preparation and over-tightening.
PHOTO 10
With the coolant neck gently placed in a vise, a flat file can be used after the gasket is removed to determine if the part is warped. If crooked, the pattern created by the file will not be even and will miss some areas.
PHOTO 11
When servicing the cooling system, a Scotchbrite pad is excellent for cleaning corrosion from connections on the thermostat housing, water pump, engine block and heater core. Always lubricate the nipple with antifreeze or spray silicone before installing the hose. This will allow the hose to slide on freely and fully seat.
PHOTO 12
When installing a new lip seal, such as in a timing cover, it is important to clean the surface where the seal sits so that it will be seated squarely, providing the proper relationship with the moving part it will seal–in this case, the crankshaft snout.
PHOTO 13
It is a good idea to place a smear of RTV around the exterior of a lip seal to act as a lubricant and have it seal to the part better. Even though the rubber is the seal, oil can migrate between the part and the exterior of the seal, causing a leak.
PHOTO 14
A lip seal needs to be tapped gently into place with either a proper tool or a socket that will ride on the metal part of the seal. The open part of the seal faces the engine.
PHOTO 15
With a new lip seal, always lubricate the rubber with system fluid before the part is installed. Whatever the seal is going to control should be used as the lubricant. For example, if the seal is going into an automatic transmission, that fluid should be the lubricant.
PHOTO 16
The best way to install a rope-style rear main seal is with the crankshaft removed. Use a dowel made of wood or steel to gently roll the seal into the engine block and fully seat it.
PHOTO 17
A neoprene seal can be used in place of a rope seal on many engines. Rear main seals are an issue today. Watch for a future installment of this series dedicated to the proper procedures.
PHOTO 18
It is hard to believe, but over time a rubber lip seal can cut a groove into the harmonic balancer hub, allowing the oil to leak. Inspect the balancer and, if the hub is grooved, a “saver sleeve” can be installed. These are available for a variety of popular applications, and will allow the lip seal to do its job without having to buy a new balancer.
PHOTO 19
There are many different sealers on the market today. It is important to read the manufacturer’s instructions and follow them. For example, RTV needs to be applied at a temperature of 65 degrees or warmer. It will not work outside on a 30 degree day, and your repair will most likely leak.
PHOTO 20
On most V-8 engine intake manifolds, it is better to use RTV as the end-rail seal, instead of using the kit-supplied rubber or cork gaskets. This is due to the difference in angles from the block and cylinder head, as a result of deck machining.
PHOTO 21
Freeze plugs in the block or cylinder head should be treated with a smear of RTV and then driven straight in with the proper tool.
PHOTO 22
Often, a seal leak can be minimized or eliminated with the proper swelling agent. Many of the lubricants produced today are not engineered to work with older-style seals and may actually cause the seal to shrink and leak. It is important to try a stop-leak product that claims to work through swelling the seal, and not something that will plug the system with an air-based hardening agent.
PHOTO 23
When working with a sending unit or engine gallery plug, a thread sealer should be applied. Most mechanics have better luck with a paste sealer than with Teflon tape.
PHOTO 24
Oil gallery plugs that are internal to the engine should be installed dry, since you do not want the thread sealer to accidentally plug an oil-feed passage. Gallery plugs external to the engine can use a sealer.
PHOTO 25
Carburetor fasteners should be tightened with a nut driver to limit the amount of torque. It is very easy to warp these parts by over-tightening. If the gasket is good and the bolt snug, it will not leak unless the part is warped.
Source
Jim Taylor Engine Service
120 South 5th St. • Phillipsburg, New Jersey 08865
908-813-3456
