Frequently Asked Questions

Q:  Who is responsible for the mounting of the transmission to the engine?

A:  If we fit it then we will take responsibility for the mounting and support to the engine in a new vessel.  If we don't, that responsibility lies with the engine supplier or fitter that has undertaken the process.

Q:  Who is responsible for the mounting / support of the transmission to the vessel?

A:  If we supply and fit then Pacific Driveline Ltd will cover their work.  As there are a vast amount of options that can be applied to support bracketing to allow for movement under thrust, there is no universal answer.  Twin Disc supply some generic advice but each application must be viewed on an individual requirement.  If Pacific Driveline Ltd are not contracted to do this work – either design or supply and fit then it becomes the responsibility of the engineers that are fitting the engine, transmission and drivetrain to the vessel.

Q:  Who is responsible for transmission ratio selection?

A:  This can only truly be quantified by the propeller supplier as the chosen reduction has a direct effect on the applied torque and thrust – to match the hulls resistance.  Some engine suppliers have this capability.

 Q:  Will the same transmission operate the same in different vessels?

A:  No – different vessels have different characteristics (apparent after sea trial) and as such input-coupling changes may be required at the owners expense.

 Q:  How important is the interaction between transmission and control system?

A:  The relationship is critical to ensure that the correct amount of engagement is achieved & the engine input speed is correct when transmission engaged.

 Q:  What is Torsional Vibration?

A:  The periodic variation in torque of a rotating system.  Causes of torsional vibration are typically gas pressures in internal combustion engines creating peak torques, inertial unbalance or irregular torque requirements of rotating equipment.  It is important to note that torsional vibration calculations are typically analysed for the continuous steady state, rather than the transient start-up or run-down condition.

 Q:  Who is responsible for ensuring torsional compatibility?

A:  “Disregarding propulsion system torsional compatibility could cause damage to components in the drive train resulting in loss of mobility. At minimum, system incompatibility could result in gear clatter at low speeds.

The responsibility for ensuring that the torsional compatibility of the propulsion system is satisfactory rests with the Boat builder, Vessel Owner and or assembler of the drive and driven equipment.

The engine builder, marine survey societies, independent consultants and others can make torsional vibration analysis. Twin Disc is prepared to assist, if requested, in finding solutions to potential torsional problems that relate to the equipment of Twin Disc Inc.’s supply.”

 Q: Who pays for the Torsional analysis?

A: The vessel owner.

 Q:  What is gear clatter?

A:  Backlash experienced between gear teeth @ low RPM. The effect is normally noise and can be improved by applying a more suited input coupling. This is only discovered after sea trial so expenses related to any changes are the owner’s care.

 Q:  Is the transmission tested after rebuild?

A:  Yes – any transmission rebuild in our workshop is “spin tested” (no load) in a similar manner to that used in the Twin Disc assembly plant. This is to ensure that specified running pressures are achieved and there are no oil leaks before installation back into the vessel.

 Q:  What are common transmission failures?

A:  Clutch Failure due to low oil pressure – caused by not fully engaging control levers, damaged piston rings, damaged oil pump, poor flow rate thru G/Box coolers or loss of oil.

 Q:  What happens if there is a vibration?

A:  Pacific Driveline do not accept any responsibility for vibration levels on sea trial as the resulting combinations of machinery and vessel make it impossible to pre-define a level of tolerance unless an in-depth design study and TVA is undertaken by the client before any equipment is fitted to the vessel.

 Q:  How often should I check the oil level?

A:  Daily or every 10 hours of operation. Check at normal operating temperature with engine running at low idle and transmission in neutral.

 Q:  How often should I change the oil?

A:  After the first 50 hours and thereafter every 1,000 hours of operation or 6 months whichever occurs first. Check lubrication plate for oil specifications.

 Q:  Should I fit oil gauges?

A:  Yes, fitting of oil pressure gauges on the transmission is strongly recommended and considered imperative where trolling valves are fitted.  Fitting of oil temperature gauges is also good but not as important as pressure gauges.

 Q:  Can you connect battery power directly to the Fema valves on a MGX Transmission?

A:  No.  Damage will result to the solenoids and clutch

Please follow this link to read the Pacific Driveline Terms and Conditions of sale.

Q: Can a Isoflex coupling take any form of Vibration

A: NO - a Isoflex coupling is designed as a vibration dampener only. Any angle / offset misalignment will damage the Isoflex coupling.

Q: How important is the alignment  procedure.

A: This is extremely important to the life of a Isoflex coupling. The gearbox output flange and shaft half coupling must be within 0.003" in face to face angle. The flanges must NOT be offset in any way i.e., vertical or horizontal.

Q: Can alignment be achieved when the vessel is out of the water.

A: NO - temporary procedure can be done but the alignment needs to be checked and completed when the vessel is in the water loaded in max running trim.

Q: Can a Isoflex coupling deform under load.

A: Yes - but only due to misalignment either at rest or when max thrust is applied to the engine - which can dramatically alter the true alignment if the engine mounts are too soft.

Q: How do I know if Isoflex coupling is correct.

A: Isoflex have a vast range of couplings that are individually rated to particular gearbox. PDL staff can make this selection.

Q: Can I simply bolt the coupling in place after the alignment procedure has been completed.

A: Yes - however Isoflex require a certain sequence and torque which is stated in the installation instructions.

Q: Do I use locktite type product on the bolts.

A: No - use anti-seize grease, the bolts are supplied with spring washers.

Q: Is there a "Get home" procedure if the coupling fails due to impact damage on the drive line.

A: Yes - if the driveline has been set up correctly the gap between the forward end of the propeller boss and the aft end of the strut will be greater than the width of the Isoflex - so when in trouble the Isoflex coupling can be removed and the flanges hard coupled as a temporary option. NOTE: If a rope cutter is installed on the shaft then a spare steel replica on another spare Isoflex coupling needs to be fitted.

Q: Are the standard mounts supplied with my engine configured to my particular installation?

A: NO, in our experience mounts supplied with your engine are generic i.e. they are supplied with a particular model engine however the gearbox reduction can differ which results in different thrust figures which in turn results in varying amounts of axial movement. The same engine can also be fitted into a variety of different craft that have different requirements and working conditions.

Q: How important is axial movement?

A: For most installations that have down angle, drop centre or vee drive gearboxes we only want the engine axial movement to be 3mm maximum. Working within this tolerance will ensure that the true shaft half coupling alignment to the gearbox output flange will be maintained under maximum applied thrust. This reduces vibration and wear on seals and bearings.

Q: Are Isoflex mounts generic?

A: NO, Isoflex mounts are supplied on a custom basis i.e. the gearbox configuration being either in line, down angle, drop centre or vee drive, placement of the mounts, support of the bell housing, the applied thrust and working conditions are taken into account.

Q: Are all engines four point mounted?

A: NO, applied power and configuration may require four, five, six, or eight point mounting to achieve the required axial movement while still reducing the engine vibration levels throughout the rpm range. We prefer six point mounting with down angle, drop centre, or vee drive applications.

Q: What technical information is available that is relative to my particular installation?

A: Data sheets can be supplied that give Axial Load vs Deflection and Thrust (shear) Load vs Deflection, Attenuation (vibration reduction) levels. Drawings - .dxf are available.

Q: What are Isoflex mounts made from?

A: Isoflex mounts and couplings are manufactured from an engineering grade heat cured polymer alloy.
Please note: due to their inherent construction Isoflex mounts and couplings electrically isolate the engine from the engine bed and drive train.

Q: How important is the actual installation of Isoflex mounts into the vessel?

A: Due to their static nature the installation is critical to the life expectancy of the mount. Fabricated engine bracketing can be out of alignment to the engine bed. Soft rubber type mounts are more forgiving in this area - the down side is that they allow too much axial and horizontal deflection. It is IMPERATIVE that the top of the engine bed is parallel to the base of the engine mounting bracket in all planes to avoid any pre-load on the Isoflex mount base, stud and core material.

Q: How should we place the engine mounts on the engine and transmission?

A: All of the engine mounts used in an installation should be placed on or as near as possible to the crankshaft centreline. If the engine needs to be raised or lowered to the hull, the engine mount to bed base must be adjusted to obtain the necessary relationship with the crankshaft centre line.

Q: Will Isoflex mounts retain my engine should the vessel be in a 360 deg roll.

A: YES, the Isoflex mounts are designed to hold your engine in a fully inverted situation however you must ensure that they are attached to the engine bed's in such a manner that allows the mount to stay in place.

Q: Should I periodically check my engine mounts.

A: YES, most rubber type mounts should be checked every six months for compression and deflection which in turn effects shaft alignment. Isoflex mounts should be checked every twelve months for uneven compression of the cores, fastenings to engine beds and fastenings to engine brackets.

Q: Are Isoflex mounts fully resistant to diesel, petrol and normal engine lubricants.

A: YES, however the studs, nuts and washers are "Gold Passivated Zinc Plated" and over a period of time they may suffer from rust. We recommend that a waterproof grease or clear spray type protective coating be applied to the stud, nuts and washers every twelve months.