Engine mounts are essential to the proper functioning of any motorized vehicle. From automobiles to airplanes to industrial equipment, engine mounts make equipment run quieter and last longer. Also known as motor mounts or isolators, these parts ensure that the engine stays in place and provides the important function of absorbing energy from the engine being transferred to the rest of the system. In specialty equipment and vehicles, traditional engine mounts don’t always work or are selected incorrectly, which can lead to the system actually amplifying the vibration rather than reducing it. This is why many manufacturers turn to customizable engine mount design and analysis for their needs.
When designing rubber engine mounts, there are a variety of aspects to consider such as materials, cost and function. There are all kinds of engine mounts that all come in different sizes and types, selecting the right one can be a daunting process. However, through customization processes and analysis, the engine mount can be designed to meet certain specifications and optimize performance of the system.
At RPM Industrial Rubber Parts, we help clients design the part that they are looking for. We have expert engineers and helpful staff who are ready to walk you step-by-step through the analysis, design and manufacturing process. We have a wide variety of standard rubber isolation parts with the ability to produce custom components for special and unique applications.
Here are the topics covered in this design guide:
What is an Engine Mount?
An engine mount is exactly what it sounds like: it holds the engine of a vehicle or piece of equipment in place. The engine and transmission of a vehicle are attached to one another. In many cases the engine mounts need to do more than just hold the engine to the chassis, they also need to absorb the energy (vibration) produced from the engine from transferring to the other parts of the equipment.
The basic principle is how to strike a balance between the amount of energy absorption and the movement that can take place (sway space). A piece of equipment may use anywhere from 3-8 mounting points, some for the transmission and some for the engine, to hold everything in place. Understanding how these work together and influence how the system performs is where the detailed experience and analytical tools come into play.
Engine mounts are also used as vibration dampeners, in effect they are absorbing energy from the system and generating heat. This is often why rubber is the material of choice when it comes to engine mount design, it has excellent damping and heat dissipation characteristic with a high degree of design flexibility. The main goal of a vibration mount is to create a rubber break between two mating systems (engine and chassis). Rubber and elastomers work better at absorbing vibration and noise than virtually any other material, especially when compared to metal or solid engine mounts.
While, for the most part, it is easy to get a hold of a replacement mount, sometimes the part is discontinued or difficult to obtain. This is a situation in which designing a motor mount is especially helpful.
Parts of an Engine Mount
Since the purpose of an engine mount is to provide a break between two systems. The most common parts used in an engine mount are the rubber body, sleeve bushing or bonded plate and the connection bolt. The rubber section can be made from a number of different elastomers that we will cover in another section. This is the critical piece in terms of absorbing energy from the system. The corresponding bonded sleeve or plate is typically made from carbon steel and adds strength and mounting flexibility. Lastly, the bolt is used to attach the mount to the engine, transmission and support structure.
Some engine mounts may be much more complicated than this and others may be as simple as a bushing and a bolt. Depending on the engine mount used, additional parts may be necessary.
Engine Mount Replacement
Just like many other parts in a vehicle or piece of equipment, engine mounts can become worn and may need to be replaced after some time. Here are some ways to tell if an engine mount needs to be replacement:
- Excess noise such as clanking or banging coming from the engine.
- Abnormal, excessive vibration.
- Engine damage or broken components.
- Misaligned or imbalanced engine that is most noticeable when one side of the engine rests lower than the other.
- Visible damage or deformation of mounting components
System Analysis for Mounting Strategies
When designing an engine mount, it is important to first analyze the proper mounting strategy. Here are a few data points used as a starting place:
- Weights of components
- Engine type
- LG location of components
- Mount locations
- Mass moments of inertia
- Idle and operating speeds
- Max output torque
All of this, and more, is included in our document titled Data Required for Engine Analysis that can be requested in consultation with our engineers. .
Sometimes, customers may already have existing documents with all of this information. Our team can use those documents instead of requiring them to fill out the data. To complete our system analysis, we use a software called Harmony. This software analyzes static and dynamic loads, nonlinear mount properties and single/multi body systems. Essentially, Harmony provides a model that we can use to look at different mount styles.
Two types of analyses will occur after the Harmony model is created:
- Static analysis: for the engine weight and torque to ensure that the mount can handle the load.
- Dynamic analysis: for natural frequencies and engine disturbances that can affect how the engine mount works.
After the Harmony model and the two above analyses are completed, our team will have everything they need to choose the best engine mounts for the job. All of this turns into an output form, which summarizes the data and describes which mounts are recommended. Proper analysis is imperative to choosing and designing an engine mount. If it is analyzed incorrectly, then the input can become amplified which makes the problem worse. The analysis ensures that the system is in complete isolation within the operating range. Although it is easy to simply choose a part from a catalog based on what others are doing, it is important to consult with an engineer first to analyze what you actually need.
Analysis is the first step, then the application is the second consideration
Engine Mount Applications
One of the biggest challenges when it comes to engine mount design is knowing what engine mount is required. With so many types, applications and industries, knowing what you need is complicated. The first thing that is considered when choosing an engine mount is the application. Here are some common applications that are taken into consideration:
- Off-highway and rugged terrain vehicles, such as in forestry
- On-highway and smooth road vehicles, such as in mass transportation
- In-plant stationary machinery, such as air compressors
- On-site equipment that is transported, such as power generators
Choosing an engine mount is reliant on the analysis and the application. For example, a stationary application typically would only require isolation in one direction and not need to be safetied. Whereas an off-highway application will be subject to high rebound loading and thus different considerations need to be taken. Each application has different load requirements, life cycle requirements and more. When this is taken into account then the engine mount will be better suited for the job.
It is important to remember that downtime equals money lost. It may be surprising, but choosing the right engine mount means less downtime and therefore more profit.
Downfalls of Choosing the Wrong Engine Mount
One of the biggest mistakes that is made in choosing engine mounts is continuing to order the same part year after year. If a customer switches from a Caterpillar engine to a John Deere engine and chooses the same engine mount, then there can be some serious complications. Here are some complications that may occur:
- Failing engine sensors
- Input amplification
- Broken engine brackets
- Reduced life cycle
- And more
When the engine or power plant is changed, even if it is only changed in a small way, then the dynamics of the entire system changes. When the dynamics are different, a different engine mount is required. If the engine mount is not changed then the performance will reduce. This is where an engineer comes in. They can explain how your system has changed and how a different engine mount will increase performance and reduce damage.
Types of Engine Mounts
There are a few different kinds of engine mounts. Many are specifically suited for defined applications and equipment. Here are four of the most common types of engine mounts:
Center Bonded Mounts
These kinds of motor mounts work to isolate shock, vibration and noise. They are very basic in design so that installation is easy and straightforward. They are versatile for applications that require isolation in one main direction. Center bonded mounts can support heavy shock loads, which brings comfort to the operator and decreases wear and tear on the machinery.
These engine mounts are used for a variety of applications including portable equipment, mobile and transport-mounted machinery and automobiles. Center bonded mounts are common in vehicles and machinery within the industrial, automotive, railroad and marine industries. The installation process is quick, easy and inexpensive, making them an excellent choice.
Two Piece Mounts
This is one of the most commonly used engine mounts. Similar to the center bonded mounts, its main difference is that it handles vibration inputs from two directions (think rebound loading) which makes them ideal for rugged or off highway applications. Its simple design can be made from a variety of energy absorbing elastomers to provide a great deal of flexibility in terms of both function and application. A two piece motor mount works to absorb noise and vibration of dynamic forces from all sides. The mount is designed to limit the forces to both sides of it, rather than all around.
These kinds of mounts are perfect for industrial, construction, on-highway and off-highway vehicles and machinery. Two piece engine mounts provide the best comfort when it comes to shock and vibration. As many OEMs know, using the right engine mount decreases worker discomfort and increases machinery lifespan.
Hydraulic\Viscous Engine Mount
Hydraulic motor mounts contain a combination of rubber elastomer and a fluid filled chamber to dampen energy. In basic terms the mount has a fluid filled internal chamber where the fluid is forced through an orifice in order to dampen energy rather than being only elastomer. The result is a much higher factor of damping characteristics that can be achieved over just using only elastomers.
One of the main benefits is to provide a much more specific damping profile for application as the fluid chamber can be tuned to the application. This requires a bit more analysis and application work. However, it is a great choice for applications that demand specific performance. These engine mounts are much more complex than other kinds of mounts due to the addition of the hydraulic fluid.
Hydraulic mounts are most common in vehicles with three to four cylinders as these provide the greatest amount of noise and vibration challenges.
Conical mounts are one of the best engine mounts on the market. They provide high load bearing capabilities and high quality vibration dampening and noise reduction. Conical mounts are an excellent choice for both off-road and on-road vehicles and machinery. With conical mounts, OEMs can choose from a wide range of stiffness which will affect the vibration absorption features.
Conical mounts are easy to install and are long-lasting. Machine operators can feel at ease knowing that their conical engine mount will stay in great shape and keep them comfortable.
Industry Usage of Engine Mounts
If a vehicle, equipment or machinery requires an engine, then it requires an engine mount. Because of this, there are all kinds of industries that buy and use engine mounts. Every engine has some sort of imbalance to it, which produces energy inputs to other portions of the equipment. Engine mounts absorb this energy and prevent it from transferring to other places where it might be unwanted. Consider connected sensors or component brackerty, cowlings and panels and operator cabs.
If energy is allowed to transfer to these other systems, then you get component failure or unwanted noise and vibration. This will lead not only to premature failure, but it also gives the perception that the equipment is of poor quality. Quiet machines are always perceived to be better quality than noisy ones. The industry that requires the engine mount also makes a difference in the type of engine mount used and what systems are more important to isolate.
Take a look at four industries and how they use engine mounts:
Construction and Agriculture
There are many different construction and agriculture vehicles that require engine mounts. Dump trucks, excavators, mowers and backhoes are only some of the machines used in these industries that need engine mounts. These heavy duty machines already produce so much noise and vibration that it is extremely important that the engine stays still. Properly selected engine mounts prevent mechanical noise and vibration from damaging connected components and help keep the operator in a quiet environment. Motor mounts keep vibration and noise down, while also keeping the equipment in service. All of this means less downtime and greater productivity.
Engine mounts also protect the internal workings of the machine. Because the engine of a construction or agriculture machine works so hard, keeping it secure extends its lifespan and reduces wear. We have a great deal of experience, not only analyzing the system to choose the best option, but we can make sure your mount system is not making the noise worse!
Similar to the automotive industry, mass transportation vehicles also require engine mounts. Streetcars, trains, buses and shuttles are only a few examples of the various mass transportation vehicles used daily. These vehicles not only need to be in service for long periods of time between maintenance, but they also need to be quiet to ensure the health and safety of the users. We offer many solutions to mitigate these common and sometimes complex questions.
General Industrial and Power Generation
Engine mounts are not only used in mobile equipment, there are a number of applications where engines are used to power an application that will still need to be isolated. Power generation is the most common in this area. There are some unique advantages in terms of isolating these systems as they tend to be more stationary in nature. In traditional off-highway applications, a unit is stationary or does not require it to move around too much. In this case, the need for excess isolation is eliminated. Not only do engine mounts hold vital parts in place, they also help the engine last longer and sustain less damage.
The most common type of engine mount for automotive applications is traditional, front/rear mounts. Each car manufacturer uses a different mount design that is specially fitted to the vehicle. For example, six cylinder vehicles use hydraulic mounts more often than other kinds
Mounts for marine vehicles look different from any other application. A marine engine mount has a wide rubber base and a metal cap that sits on top of the base. Through the cap is a washer and bolt system that allows for height adjustment.
Marine engine mounts are perfect for reducing vibration and shock. This is especially important in speed boats where the engine becomes worn down quickly. There are typically multiple motor mounts that are used in boats to keep the engine steady. They may be attached to the front and rear or to the sides of the engine.
Manufacturing Processes of Engine Mounts
Engine mount analysis is not only important for existing parts in a catalog, it is also important for custom design. Sometimes, once the engine mount analysis has been completed, you may not be able to find the part that you need in a catalog. Through custom engine mount design, there are two processes in which the mount is designed and manufactured:
Reverse engineering is the process of designing and manufacturing a part that already exists. There are a few reasons why you may want to reverse engineer an engine mount:
Through reverse engineering, a previously used part can be used to design an entirely new one based on the same specifications. Reverse engineering is a great way to get the same part you have loved for years, but made in accordance with the analysis.
- The mount was discontinued
- The mount no longer fits your standards
- The materials of the mount have changed
- You cannot order the correct quantity, material or size
Unlike reverse engineering, prototyping is used for parts that are completely unique. Here are some of the reasons why prototyping may be used:
If you have a machine or vehicle that requires a special engine mount then prototyping is the best design solution. With this process, the client will receive multiple prototypes and variations of the part until it is exactly what was envisioned. Once the prototype is approved, the part will be manufactured.
- The part required is entirely unique to your product
- You need specific dimensions that may not be offered as a standard part
- You want to test a unique part before requesting full volume production
- The part requires a special material not customarily offered
Engine Mount Materials
Just like most parts, engine mounts may be made out of a few different materials. How do you determine the best material? Generally there are two components: the rubber section and the substrate that it is bonded to.
Rubber Engine Mount Materials
The rubber piece is one of the most important aspects in designed engine mounts. The chosen rubber can have a dramatic impact on vibration, noise and stability. Here are some of the most commonly used rubber materials in engine mounts:
- Natural rubber: high vibration absorption, fatigue resistance and resilience. It is by far the best material for vibration mounts as it has the highest resiliency rate (ability to return back to original form). Unfortunately, natural rubber is not as resistant to heat and chemicals as other polymers may be. This rubber material is one of the most cost-effective polymers, which makes it popular for engine mounts.
- Neoprene: high tensile strength and abrasion resistance. Best used for cases where there is constant oil for fuel exposure. While our standard natural rubber mounts can handle the occasional oil spray or drops that are common in engine bays. Constant contact will degrade the elastomer over time which is where Neoprene shines.
- EPDM: sometimes used but in highly defined cases, as EPDM parts may have low flame and tear resistance. EPDM is best used in cases that involve UV exposure or direct sunlight. EPDM can be produced with a wide range of tensile strength/rigidity which can be beneficial for certain applications.
- Silicone rubber: moderately suitable material in some cases but has low tear and abrasion resistance.
Overall, natural rubber, Neoprene, EPDM, and silicone are some of the best materials to use for rubber engine mounts. Talk with a rubber manufacturer, like RPM Industrial Parts, to learn more about what kind of polymer is best for the engine mount you need.
What about the metal substrate? Here are some of the metals that may be used in an engine mount:
- Stainless Steel
Low Carbon Steel is the most commonly used metal in engine mounts because it is cost effective and strong. However, aluminum is also a top contender for engine mount metals because it provides higher strength and a lighter weight. Although it does come at a higher cost than steel. Iron, brass and stainless steel are used on a case-by-case basis due to weight, magnetism and corrosion resistance.
The key point in which substrate to use, is also to have knowledge of which adhesive to use to bond the rubber to the substrate. Not all adhesives are created equally. In fact, we are pretty fananatical about the bond, as it should always be the strongest part of the component. Meaning, the rubber will fail long before the bond between rubber and metal.
Rubber to metal bonding allows us to create many different possibilities to solve a number of tough challenges. The metal part of the engine mount is what connects to the frame of the vehicle while the rubber part is what connects to the engine. This allows for the sturdiest design without high vibration or noise.
Benefits of Using Rubber Engine Mounts
Rubber engine mounts are recommended for a variety of reasons. Take a look at some of the benefits to using rubber engine mounts:
- Provides excellent damping and energy absorption.
- Superior noise and vibration dampening and heat dissipation.
- Provides stability at the right hardness.
- Broad elastomer range for different applications.
- Long lifespan even with consistent pressure, oscillation or vibration.
- Resistant to oil, water, ozone and other damaging things.
All of these benefits depend mostly on what kind of rubber you use for the mount. A natural rubber or Oil Resistant Neoprene are the most common for most applications for meeting all the benefits above. Compared to solid engine mounts, rubber provides a safe alternative that is sure to last a long time.
Engine Mount Cost
Sometimes engine mounts go bad or need to be replaced. Engine mount replacement cost depends on a few factors:
- Materials and size of the mount
- How many are required
- Type of vehicle or equipment
- Type of mount required
An engine mount for a bus or a truck is going to be far more expensive than that of a car or a small boat. Traditional motor mounts typically cost between $50 and $200. Specialty motor mounts, designed for uncommon or larger vehicles, may cost between $150 and $500. These costs do not consider labor and installation, which can add a few hundred dollars more to the total.
For mass production of engine mounts, OEMS and other customers can expect to pay thousands of dollars. This factors in cost of materials, equipment and labor.
At RPM Industrial Rubber Parts, we specialize in mass producing these kinds of customized rubber parts. Contact us to get a quote.
Molding Processes of Rubber Engine Mounts
There are a few different ways that rubber parts are molded. When it comes to engine mounts, the rubber part is integral to the mount’s function. The rubber on a motor mount provides many benefits:
- Vibration and noise dampening
- Stability and hardness to limit motion
- Reduced wear on the engine
- Flexibility and tear resistance
- Protection from environmental conditions, such temperature and fluid exposure
The rubber on an engine mount can be molded in a variety of ways, here are the three main ways:
Injection Molding for Engine Mounts
Injection rubber molding is one of the most common methods of manufacturing rubber. Here is how injection molding works:
- The rubber stock is heated and inserted into the injection nozzle
- The nozzle is injected into the sprue where the rubber enters the runner
- The mold cavities are filled with the rubber stock
- The mold is cured using pressure and vulcanization
- The parts are removed from the mold and excess flash is taken off
For isolation mounts, natural rubber is most commonly used in injection molding, but many other polymers can also be used. Natural rubber is often the best choice as it has a wide range of flexibility and offers the best resiliency or rebound characteristics, meaning it rebounds back to original shape very easily.
Rubber injection molding is best for high volume production and complex parts. Because rubber engine mounts are not incredibly complex, injection molding is not required for this part. However, it is the fastest method of production.
Compression Molding for Engine Mounts
Compression molding is another popular method of manufacturing rubber parts. It is generally used for simple applications where the complexity is low. Here is how compression molding works:
- Unheated rubber stock is placed into the mold cavity
- The rubber stock is compressed by the two halves of the mold cavity which rest on heated plates
- The heated plates soften the rubber so that it fills in the spaces of the mold
- The formed rubber is cured and vulcanized in high heat and pressure
- The rubber part is removed from the mold cavity and excess flash is cut off
Natural and synthetic rubbers are typically used for compression molding. This is because these rubbers are the hardest and are not as easily injectable, making them perfect candidates for compression molding.
There are many benefits to using compression molding. The most important is that it costs less due to inexpensive tools and machinery. Compression molding also results in decreased material waste, which reduces costs. However, compression molding is best for low volume production and larger, less complex parts.
Transfer Molding for Engine Mounts
Transfer molding, a combination of compression and injection, is the last method of rubber molding. Here is how transfer molding works:
- The rubber charge is placed into the transfer pot
- The plunger is insert into the transfer pot and the rubber charge is heated onto all sides
- Once thoroughly heated, the rubber will transfer down the sprue and into the mold cavity
- The formed rubber part will be vulcanized and cured at a high pressure
- The rubber part will be removed from the mold cavity and trimmed
Similar to compression molding, harder rubbers such as natural rubber are best for transfer molding. The finished product will turn out harder and have better vibration control.
The advantages of transfer molding include better uniformity and more advanced accuracy. Transfer molding is best for complex parts that need to be produced at low volume. The downside to using transfer molding is that it can be more expensive and slower than compression and injection molding.
Rubber to Metal Bonding in Engine Mounts
The rubber to metal bonding process looks a little different for each part. The rubber in engine mounts aren’t always bonded to the metal part. Sometimes they are manufactured separately and assembled together later. Here’s the basic process for bonding rubber to metal:
- Pick an elastomer for the application
- Prepare the metal substrate (blast, degrease)
- Prime the metal and rubber parts (not always necessary)
- Apply adhesive to the metal part
- Mold and bond the parts together
- Test to ensure bond strength (bond should be the strongest part)
Injection, transfer and compression molding are the most common methods of creating a quality rubber to metal bonded part such as an engine mount. Depending on the complexity and requirement of the part there are a variety of reasons why we chose to use one over the other. The end result is to make sure we are producing a quality part that is purpose built for the application.
Rubber Design Analysis Services
It can be difficult to know which engine mount will work best for your machinery. Sometimes the part that you have been using for years suddenly no longer works. That is where RPM Industrial Rubber Parts steps in. We have an analysis process that can help you figure out exactly what kind of rubber engine mount you need. Take the guesswork out and turn to a company you trust.
Even once we have helped you analyze what engine mount you need, you may not be able to find it. At RPM, we can help you customize the engine mount you are looking for. The custom design process is easy with our team. We will help you come up with a design plan that will include dimensions, materials, color and shape of the part. Then, we will mold the part and send you prototypes until you get exactly what you’re looking for. Once the prototype has been accepted, we will manufacture the part at full volume and ship it to you.
We also offer standard rubber parts at RPM. Take a look at this list of some of our available mounts:
- Small industrial engine mounts
- Rubber flex sandwich mounts
- Center bonded mounts
- Two-piece mounts
- Machinery mounts
- Binocular engine mounts
- And more
Engine mounts are not the only standard parts that we offer. From grommets to o-rings, RPM has got exactly what you need. If you are interested in our custom rubber services or standard rubber parts, visit our website, https://www.rpmrubberparts.com, or contact us at (888) 842-5668.