Morgan three wheeler drive train.
The Morgan three wheeler uses an S&S X Wedge engine built in the United States and this is coupled to an intermediate shaft which carries the clutch at the other end. The coupling is made
by Centa UK and has been derived from a small marine coupling. Centa specialise in well designed marine engineered couplings and the Centa unit fitted to the Morgan three wheeler is no exception.
The Morgan three wheeler coupling has been modified to absorb shock in both directions. In my opinion those modifications allow too much free play at the centre of the rolling action of the rubber cylinders.
The original inserts are slightly barrel shaped to allow for some degree of misalignment. In my opinion the bearing in which the intermediate shaft runs and the spigot bearing in the clutch are both at
risk from the lack of centering provided by the Centa coupling inserts. Being rubber and having distortion as a major part of the shock absorber function they allow the shaft to run out of true.
This is the normal function of a marine coupling which connects a rigidly mounted gearbox output shaft and the stern tube / propellor shaft assembly mounted in the hull, which will be carried in two
well spaced bearings. The Centa coupling is flexible in nature to allow for the inevitable misalignment due to both items being mounted in the boats hull which will flex due to enormous pressures from the
sea and also from thermal expansion.
The clutch is well mounted on the end of the intermediate shaft an carries the spigot bearing which supports the gearbox input shaft. A sturdy and smooth acting gearbox is mounted on rubber mounts
to the chassis with a conventional propellor shaft between it and the Bevel box. The loud whine emitted by the bevel box has been addressed by fitting two fabricated beams to the bevel box.
These are in turn mounted back to the chassis using cylindrical rubber engine mounts of the silent bloc type. This mounting arrangement is known as the NVH kit and was retro fitted to early Morgan
three wheelers. The Morgan three wheeler suffers great vibrational issues due to the flexible nature of this NVH kit which allows the input shaft of the bevel box to rise under hard acceleration.
When the bevel box " nose" rises in this way slack is introduced to the top run of the final drive belt, when the bevel box nose falls again the opposite occurs and the final drive belt comes under increased
tension in the top run. At certain engine speeds this becomes a harsh vibration, felt acutely because it affects the whole of the transmission from back wheel right through to the engine crankshaft.
It is vital that the shaft of the bevel box remains parallel to the output shaft of the gearbox or further vibration will be generated by the Hardy Spicer joints in the prop shaft. It is impossible to know how
much misalignment occurs as the bevel box nose lifts but whatever the magnitude, it can not be good.G