The Tiger's engine was water-cooled, and heat was extracted from the water using two large radiators with two fans each. The fans, in the extreme rear of the hull, were driven by the engine through their own gearbox.
Two kinds of engine were used in Tigers, HL210 and HL230, and for each the gearbox arrangements were different. This page describes the fan drive for the HL230, which was different to the HL210 fan drive.
The large HL230 engine did not leave much room behind it, so a small gearbox for each fan was mounted on the side walls of the engine compartment. These gearboxes seem to have been mirror images of each other.
Seen from inside the engine compartment, this is the left-hand wall. The largest circle on the left is the opening in the wall that leads to the fan drive. Attached to it, and slanting downwards, is a fan drive gearbox. At lower right the gearbox has an angled attachment point for a drive shaft from the engine. At extreme lower right, the gearbox is fixed to the wall by a bolted mounting.
Center right is the air hole in the wall. Note that the movable valve in this air hole is scratched out ; it was part of the underwater sealing gear and was supposed to be removed. It is interesting that the connecting rod that moved the valve is drawn immediately above the hole; on the Bovington vehicle, it is below. There must have been a design change in the meantime.
Running down through the middle of the diagram is a cooling water pipe coming from the left-side radiator. There are some narrower water pipes that connect the wide pipes, presumably they were for pressure relief? They are scratched out too, so they must have been necessary for underwater travel. I can't figure it out!
At top left there is a crossbeam that runs over the engine compartment to support the cover plates. This, according to the diagram, must be sliced down from 60mm deep to 45mm because the HL230 is larger, "if a new beam is not available".
Click on this thumbnail to see the left-side fan drive gearbox from behind. Note that the draughtsman has made a mistake: he has drawn the left side of the tank as seen from the rear, but pasted in a profile of the right-side gearbox as seen from the front! The outline is the same so perhaps he didn't care.
The right-hand fan drive is shown in the next two pictures. It seems to have an extra fitting; a sort of funnel leading down from the top left of the diagram. Perhaps they both had this? The funnel mouth would have been immediately accessible if the engine cover plate were opened; it is not a round funnel, it has a narrow oval mouth which fits better inside the cramped engine compartmnent.. The plates and hinge shown at the top of the diagram are actually the radiator cover plates. The large circle at the bottom is the exhaust cowling.
Click on these thumbnails to see the right-side fan drive from the side and from behind. Once again, the draughtsman has mixed up his viewpoints.
