High Performance Engine and
Suspension Mounting Systems
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  • Harley Davidson


  1. How does the Dyna engine mount system work
  2. I replaced the mount on my FXR with an original equipment part but the bike now vibrates too much, why?
  3. What are the benefits of using Predator VCS engine mounts?
  4. How do the engine mounts improve handling?
  5. I have seen the term “NVH” used. What does this mean?
  6. What are the causes of engine vibration?
  7. Are there specific type approval or TÜV requirements for these parts
  8. Do you only make mounts in black rubber or can I have other colours?
  9. Why do you use rubber rather than urethane?
  10. Where are your mounts made?

How does the Dyna engine mount system work

The Dyna frame originated from a system developed by Norton. This is the Isolastic mount system which was patented in the mid 70s. The basic principal is to mount the engine, transmission and swing arm as one lump in the frame. The bike is basically split into two units. The frame, tank, seat, front forks and front wheel are one unit and the engine, transmission, swing arm and rear wheel are another connected together by the mounts. All braking and acceleration forces from the back wheel are transmitted to the frame through the mounts. The mount stiffness is also critical to prevent the front and rear wheels from going out of alignment in the vertical and longitudinal axis. So it does much more than just isolate engine vibration. Where the Harley differs from the Norton is that the two bottom mounts effectively act as a knife edge and rely 100% on the top stabiliser to control the vertical alignment of the engine.

Acceleration and braking forces try to push and pull the engine in the frame through the mounts and engine torque tries to pitch it up and down at the front. In an addition the angle of the rear shocks mean that there is a constant rearward pull on the mount system under the static weight of the bike. This can lead to the phenomenon of the gap between the front mount and the frame which is often reported. The stiffest axis is the yaw axis which controls the lateral alignment of the wheels. Any displacement in this axis would give a tendency to fishtail and make the bike very unstable. To maximise this stiffness HD have come up with a rear mount which has additional interleaf plates in which increase lateral stiffness but does not affect vertical or longitudinal stiffness. This actually still works quite well.

What we have done is to change the stiffness, damping characterises and progressive rate in all three main axis of the front mount and added an integral stabiliser link to prevent side to side movement which can affect the handling of the bike. The geometry of the stabiliser is such that it does not interfere with the vibration isolation characteristics of the system. In order to optimise the performance of the mount geometry we have also raised the height of the front mount closer to the crank centre line where the thrust loads from swing arm are directed.

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I replaced the mount on my FXR with an original equipment part but the bike now vibrates too much, why?

The original mount was developed by HD in 1979, its part number was 16207-79. It was used in the FXR, FLT and FLH.

At some stage HD revised the rubber hardness to make it a “B” version which still worked fine with both Shovel and Evo engines.

Fast forward to the Twin Cam era and HD carried over the mount system but seem to have overlooked the fact that the Twin Cam is a much heavier and more powerful engine and the original mount had become overloaded. HD released a service fix for bikes that were now failing mounts (service bulletin M-1182 December 2005) and made the mount much stiffer becoming revised design version “C”. When the 96 motor came out they then upgraded it to “D”. In the evolutionary process the "D" version became almost double the stiffness of the B version but the part numbering system they used means that the part numbers are superseded so the earlier versions are made obsolete.

We think this was a mistake. They clearly never checked the backwards compatibility of the new versions as the early bikes need a much lower stiffness than the later Twin Cam engines. As a result using the "D" version can give unacceptable levels of engine vibration transmitted to the frame. We have set out to correct this mistake by tuning a mount specifically for the Shovel Head and Evo applications

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What are the benefits of using Predator VCS engine mounts?

Our products are designed to give uncompromising performance. Durability of the system is significantly improved and in many cases we have replaced OEM (Original Equipment Manufacturer) parts which have a notorious reputation for premature failure, particularly when used in performance applications and under extreme riding conditions.

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How do the engine mounts improve handling?

When developing new mounts we take into consideration the way the mount system was originally designed and how it interacts with the bike frame and suspension geometry. We aim to allow some engine movement where necessary to isolate vibration whilst eliminating unwanted movement that can affect the handling of the bike. This can mean that we have had to innovate new ways to mount the engine within the constraints of the original engine and frame mounting points. We always aim to have a product which will bolt on and does not require modification to any other components.

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I have seen the term “NVH” used. What does this mean?

NVH is a term in widespread use in the automotive industry used to describe the quality of noise and vibration inside a car. “Noise” and “Vibration” are measurable values but “Harshness” is very subjective.

The purpose of an engine mounting system is to reduce NVH to an acceptable level. Predator VCS engine mountings are designed to give excellent NVH performance without compromising engine control and handling.

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What are the causes of engine vibration?

There are two main causes of engine vibration, engine out-of-balance forces and torsional vibration resulting directly from cylinder firing.


Depending on the engine configuration, vibration caused by engine out-of-balance can be in any 1, or a combination of 6 main axis. Linear; vertical, lateral and longitudinal. Rotational; roll, pitch and yaw. Some engine configurations are inherently extremely well balanced such as 6 cylinder in-line engines, and some are very poor such as 1, 2, and 3 cylinder in line engines. Large displacement 4 cylinder engines suffer from a high level of vibration that occurs at twice engine speed, known as second-order out-of-balance. This often results in a buzzing vibration at high engine speeds on a solid mounted engine.

V engines with a 90 degree angle and forked rod ends are inherently well balanced and is the optimum layout for a V twin engine, whereas a 90 degree V Twin with side by side big ends generates an out of balance force around the vertical axis (yawing). Harley Davidson engines with a 45 degree V angle has large out-of-balance forces that have been partly corrected in the twin cam B engine which uses balance shafts. These balance out the primary out-of-balance forces. The characteristic of out-of-balance vibration is that the forces increase with the square of the rotational speed. In other words going from 2000 to 4000 RPM and the forces increase by a factor of 4.

Cylinder firing:-

Torsional vibration caused by cylinder firing usually generates a problem at very low engine speeds where the amplitude can be quite high and the frequency relatively low. This can give an unpleasant shake at idle speed. It is particularly noticeable in single cylinder engines and odd fire engines, these are engines where the cylinder firing is not at even intervals of cylinder rotation which is the case of V engines and some parallel twins.

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Are there specific type approval or TÜV requirements for these parts

Currently there are no UK type approval or European TÜV certification requirements for engine mounts within the EU. Inspection is at the discretion of the MOT or TÜV tester as with most aftermarket parts. We work closely with the UK performance aftermarket association (PAAA) and European tuning organisation (ETO) to ensure that we are up to date on legislation in this area.

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Do you only make mounts in black rubber or can I have other colours?

As Henry Ford said “you can have any colour you like so long as it’s black”. We use the same principal, for almost the same reason!

The black colour is carbon. As with other engineering and automotive applications of carbon it’s used to control some of the most critical characteristics. In the case of rubber it is strength, stiffness, abrasion resistance etc. In Henry Ford’s day it was used as a pigment to make black enamel paint. In the early part of the last Century, resin based paint containing carbon was a much more durable finish and dried quicker than other colours, so painting all the cars black was a faster process. The time taken to paint a car was a bottle-neck in Model T production so Henry standardised on black! We don’t need to worry about speed but the increased durability and strength you get from carbon is important.

Rubber can be moulded in other colours but at the sacrifice of some important characteristics. We don't compromise on performance, so we only ever use black rubber!

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Why do you use rubber rather than urethane?

We use the best materials and technology available to get the job done!

Urethane is superior to rubber in its abrasion and chemical resistance which is why it’s used in tyres for fork lift trucks, mud flaps etc. OEMs sometimes use it for suspension bump stops because of its abrasion resistance. It is also much more economic to manufacture because it's also available as a pourable resin, so mould tooling is much cheaper. Rubber moulding requires specialist injection mould tools and high temperature high pressure moulding machines.

For engine mounting applications natural rubber or natural/synthetic blended rubber is superior to urethane in every respect. Critical characteristic are:-

# Temperature range

# Resilience (stiffness/damping ratio)

# Creep and permanent set (permanent deformation)

# Elongation

# Bond strength

One of the many critical weaknesses of urethane as an engine mounting material is the change in characteristics across a temperature range, in particular its resilience. The engine bay is subject to extreme temperature ranges. Urethane is unstable under these conditions. This is why OEMS never use urethane for a primary engine mounting system.

We are the experts. Our policy is a no compromise, ultimate engine mount solution. If urethane was the best stuff to use, we would use it!

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Where are your mounts made?

All our engine and transmission mounts are designed, developed, manufactured and tested at our site in Corby in the UK.

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