Auto Service World
Feature   January 1, 2006   by Auto Service World

Revealing Look At Sealing

It is a simple fact that today’s engines are harder to seal than the powerplants that came before. An even more critical point, however, is that they are more difficult to reseal.

The reasons for the initial need for greater and greater sealing technology are many. They run the gamut from changes in the type of materials that are being used in the engines–lighter alloys, heavy use of aluminum, the increasing use of plastics in the pieces that the vehicle manufacturers attach to them–to new casting techniques that save weight, but are less forgiving of operational stresses.

Combine this with the fact that today’s car owner is less accepting of stains in the driveway, and you have an imperative that has led to the creation of a number of gasket and sealing innovations over the past few years.

Traditional copper and brass gave way to metal and asbestos in the 1950s. These were replaced by composite metal and impregnated fibre or graphite composites by the 1980s. Those were, in turn, largely overtaken by the development of the Multi-Layer Steel (MLS) gasket in Japan during the early 1990s (domestic applications trickled in a little later).

Today an estimated 80% of new engines are designed with MLS gaskets as standard equipment, and further growth is projected.

In the MLS system, multiple thin layers of cold-rolled spring grade stainless steel are coated with elastomeric material. The resilient elastomer is essential since it provides sealing of the fine surface imperfections while resisting aggressive combustion gases, oils and coolants at temperatures up to 250C.

Of course, it was never a case of one technology replacing another in one fell swoop. Many older technologies are still in use because they work well on certain applications. In some cases, older technologies are chosen for original equipment applications due to cost. At the original build stage, it can be a case of engineers building for an acceptable lifespan based on an understood failure rate.

Sometimes, of course, they get it wrong. Take, for example, two infamous cases of just how wrong the OEs can get it: the Ford 3.8 and the Chrysler 2.0. Both suffered from chronic head gasket failures.

The first generation of the Neon, built from 1995 to 1998, had notoriously short-lived head gaskets. The conventional-design gasket–of graphite composition that was specified against the supplier’s advice–simply didn’t last that long, many failing at less than 100,000 km.

When it was recognized, a longer-lived but more expensive MLS gasket design was introduced.

The issue with MLS designs typically surrounds clamping force, or rather a shortage of it.

With the introduction of all-aluminum heads and blocks and the lightening of castings, it is no longer possible to use torque values that would have been typical with preceding designs.

Take the Ford 3.8L V6, quite possibly the most famous head gasket failure of modern times. The Ford 3.8L engine found its way into a great many Ford vehicles, but a cylinder head design change meant that it had too low a clamping force to seal using the conventional gasket installed. Under driving loads and wear and tear, the head would literally end up lifting up off the gasket a fraction of a millimetre and slamming down with each repeated combustion cycle. You couldn’t see it, but the gasket could certainly feel it and would eventually fail from fatigue and the effects of hot gas leakage. This all led to a much-publicized recall of hundreds of thousands of vehicles, not to mention a revised torque-down specification.

And the effects of that were eventually written on Ford’s warranty cost balance sheet.

For the aftermarket, the risks are measured one customer at a time, with recurring sealing failures in the head gasket or other areas chronically difficult to rectify.

One possible reason for this is the reliance by some technicians on OE gaskets. What this misses is the difference in conditions at assembly.

Aftermarket head gaskets tend to be more forgiving of surface finish and flatness conditions than the OE gasket. An OEM MLS gasket, for example, might require a surface finish of 30 to 40 microinches to seal, whereas an aftermarket MLS gasket might have a different surface coating that can still seal with a surface finish of 60 to 70 microinches, more commonly achievable in the aftermarket.

Even so, there is a limit. While it is customary to send out a cylinder head for surfacing, the use of aggressive surface preparation discs by the technician to remove residue on the block left in the engine bay can cause early failure, no matter how expert the cylinder head shop. These abrasive discs can turn a sealing surface into a washboard.

One new development on this front, however, is the introduction of much more gentle surface preparation discs. The non-woven nylon fibre material impregnated with aluminum oxide mineral is said to be ideal for removing old gasket residue and preparing a surface for a new gasket. There are two basic types, some for use on steel, others for aluminum. The 3M company sells one such product as Scotch-Brite Roloc Gasket Removal Disc 07714. Norton Abrasives has a line under its Bear-Tex brand. There are surely other offerings out there. Regardless, great care should be taken to ensure that flatness or the edges of a sealing surface are not compromised.

Proper Assembly Key to Successful Repair

While the use of proper gaskets and surface preparation are critical, they can both be severely compromised by incorrect assembly procedures.

Under aftermarket conditions, the imprecise nature of sealing surfaces must be considered. Many flanges and sealing surfaces simply aren’t as straight or as strong as they once were; fortunately there are a number of products to help gaskets do their job.

Known as liquid gaskets, these are particularly helpful in flange-type applications. Products for these applications can provide a good seal with up to a 20 thou gap.

Silicone products have specific applications that they can help. These tend to be flexible, making them useful for sealing areas where movement can cause leaks. They are also useful in T-junction areas, such as intake manifolds, where three narrow sealing surfaces meet.

The key to obtaining the desired seal is using the appropriate category of gasket maker. There are different formulations for rigid parts, flexible parts, and high temperature parts, for example. Substitute at your own risk.

In a nutshell, the fact is that many aspects of engine sealing have changed, but one important fact has not: the success of a repair is in direct proportion to the care taken in preparation and assembly of every component, whether that is a head gasket or a water pump, a complex set of sealing surfaces or a simple flange.

Ultimately the customer does not care about how complex the job might have been; he just wants it done right. Thankfully, the technology is at hand to do that. All you have to do is know which technology to bring to bear and how to use it.

Special thanks to Corteco, Dana Canada Inc., Henkel Loctite, and Federal-Mogul for information used in the creation of this article.

Torque Talk

Even today’s high tech engines share a similarity with the earliest days of automotive technology: they’re still bolted together.

And, until the engineers figure out how to cast an engine and all its internal components in one piece, this will remain the case. But the use of lighter construction has made proper torque procedures more critical than ever.

Torque Wrench Calibration: No torque procedure can succeed if the torque wrench is not reading correctly. All torque wrenches should be properly stored and calibrated regularly. With regular use, they should be calibrated every year.

Threadlocker Use: When a threadlocker is used on a fastener, the coefficient of friction for that fastener changes. On critical assemblies, the applied torque specification should be recalculated. If clamp load is to remain the same, applied torque usually decreases to allow for the decrease in friction on the parts. When using threadlockers, torque the assembly using “lubed” thread specs.

Here are some additional points to ensure proper torque and clamp load.

1. Head bolts must be in perfect condition. Only clean, undamaged threads will allow for accurate torque readings.

2. Threaded holes must be round and clean. Dirty or deformed hole threads in the engine block can reduce clamping force as much as dirty or damaged threads on the bolts. Run a bottoming tap down each bolt hole in the block.

3. Lubricate bolts threading into blind holes. Add some lubrication to the underside of the bolt head, too. When bolt holes extend into the coolant jacket, use a thread sealer to prevent coolant leakage.

4. Torque-to-yield (TTY) bolts stretch when they have been properly torqued, and so it is often recommended that they not be reused. Once used, they may not provide proper clamping force, leading to possible leakage. Replacement isn’t always specified, but it may be a good idea.

5. Check bolt condition and length. Even non-TTY bolts can become stretched or damaged. Also, bolt lengths can vary on an engine. Using a bolt too long for a blind hole–whether because it is intended for a different position or is stretched–may provide a torque reading, but not clamping force.

6. Resurfaced heads may have a reduced height sufficient to require different length bolts or deeper washers. As mentioned, if a bolt bottoms out, it will apply little or no clamping force on the head and may allow the gasket to leak.

7. Don’t forget to use steel washers in aluminum applications that call for it. They prevent the galling of the surface and help distribute the clamping load.

8. Use torque sequences and values as specified, and be sure to use the latest information. Torque procedures can be amended to address specific sealing problems.

9. Make sure you have an accurate torque wrench and torque-to-angle indicator for TTY bolts.

10. Ensure that you know which applications recommend retorquing and which do not. Many modern gaskets are engineered to eliminate this procedure, but for some it is unavoidable. If a gasket requires retorquing, the engine should be brought up to normal operating temperature and shut off. Retorquing should be done while the engine is still warm on cast-iron applications. On aluminum head or block applications, the engine should be allowed to cool.

Smart Sealing Technology

If you thought that a gasket was just along for the ride, think again, because gaskets are starting to think for themselves.

The primary task of any gasket is to provide a seal. This is difficult when parts are moving in relation to each other as operating conditions change. What if a gasket could help control these changes?

That is exactly what has been developed.

Gaskets with integrated temperature and/or pressure sensors, such as the Victor Reinz SensorCS gasket shown, can lead to better control of combustion and cooling parameters at the point of combustion. This spells better fuel efficiency and lower emissions, especially at startup and in cases of autoignition and knock.

The gasket integrates temperature sensors in the immediate vicinity of the combustion chambers for temperature measurement.

Because these are close to the actual combustion process, response time can be very quick. With the right control systems, coolant flow can be adjusted to provide optimum cooling, and combustion parameters adjusted to prevent other undesirable developments.

While Dana says that the system is not currently on a production application, the company says it will be “soon.”