Per Pat's request, we are going to have an Arts lesson, a Physics lesson and a History lesson today. The history will be intermingled, fractured from the "revisionist" textbook published somewhere in Texas.
The Arts lesson begins with the fact that Pat is an Architect, and therefore skilled at drawing things, and he likes to ask me to draw thing as a joke because of his perverse and twisted sense of humor. He is not a good human being and I suspect him of deviant acts too sickening to mention among polite company.
That said, to Physics - the internals of the engine rotate clockwise. Because every action has an equal and opposite reaction, the motor itself then rotates counterclockwise to counteract this. This is the same reason why helicopters require a tail rotor, and why 2 engined airplanes have the props rotate opposite one another and why the water in the toilet rotates in the wrong direction south of the equator.
Because the British never engineered anything properly to start with and thus needed to correct their mistakes through a series of needlessly complicated and fragile constructions, we have the tension rod. Which is typically "ass backward English" in and of itself because the rod primarily works in compression, not tension, but properly naming the function of a device has never been a strength of British Engineering.
This propensity to bad engineering followed by fantastically bad re-engineering, if you are not following the textbook mechanics described above , is demonstrated repeatedly in fantastically orchestrated killing devices in British Films. I refer you to James Bond Films - Gold Finger "No I expect you to die Mr. Bond", and in Austin Powers Films - Dr. Evil "Start the unnecessarily slow dipping mechanism". You see my point.
You will note that the motor mounts are at the very bottom of the motor. The rotating mass of the crankshaft and internals are about 1/2 way up the motor vertically.
Competent engineers learned sometime during the dark ages while developing siege machines (catapults becoming trebuchets (note that that the latter is a French word...........) that led them to put the center of the rotating mass as close to the anchor (the ground) as possible to prevent catastrophe and mayhem.
Regarding levers and leverage, the further you move away from the center of the rotating mass, the longer the lever is, and since a lever's force is a function of the square of it's length....Blah Blah Blah - IF IT ISN'T CENTERED, IT'S BAD.
Again referencing the diagram you will note that the mounts are as far away from the rotating mass as possible. BRILLIANT! Because of this engineering decision, we now have a motor that wants to rotate (and does) and is making physical contact with everything around it. So, some Engineer got paid a second time to solve this problem with...........you guessed it, the "tension rod" or as enlightened engineers call it, the "compression rod" , which acts as a brace to keep the motor from rotating.
As a last bit here, in their infinite wisdom, the British Engineer made the rod adjustable. Why? if your answer is "to make it needlessly complicated and fragile" you are only partially right.
Follow me here..............Because the motor mounts are rubber, and because rubber "melts" when exposed to gas and oil and because British cars leak oil like a BP drilling rig in the Gulf, our engineers though ahead here.....They knew the mount would deteriorate and collapse under the weight of the motor. They though ahead and made their "Engineering Fix" very elegant and practical - they made the rod adjustable to compensate the motor dropping due oil leaks..............