Imp Water pump (QCP574)
The Imp water pump is quite a complex unit with the shaft running right through. It doesn't often give problems. Eventually it can leak coolant through the main impeller-shaft seal. Such a problem will sooner turn up if the drive belt has been overtightened (causing premature failure of the bearing and excessive up-and-down movement of the shaft).
The body can crack if it's treated roughly.
To ensure long life:
1. Make sure that the alignment of radiator to fan-cowl is correct, so that the rubber sleeve doesn't deform the cowl enough to cause the fan-blades to scrape under engine movement
2. Give it a twirl dry (by hand), to commence bedding the seals
3. Do the initial running with the pressure-cap cracked loose, or else use a sabotaged cap (so that there's minimal leakage before the seals can bed in)
4. Keep the pump assembly in its normal working position (i.e. with axis horizontal) for ever after. If you take the unit off for any reason, DON'T park it face-down on the fan-cowl - this is a death-sentence to the front bearing. (A little water will inevitably get to it.)
Given the above, maybe even a Q-H pump might last a while... A good overhaul of a 1970-ish pump would make most of these precautions other that 4) unnecessary, because about then they had generous water-grooves. The late Q-H ones have the same exterior, but the grooves are filled in.
Keep the correct fan belt tension (1" total movement on the belt's longest run), or the water pump will give trouble. Overtightened belts will drastically reduce life expectancy of the pump bearings and seals.
When you replace the water pump, don't take off the fan by undoing the centre nut. Undo the four bolts securing the fan to the pump boss. The replacement pump comes with a new boss.
Ferodo fan belts ref V916 listed as fitting Sunbeam Imp Sport and Chamois 1970 -on, Bond Equip GT 1968-1970 (some, V917 is also fitted to these cars), Triumph Vitesse 2 litre 1966-1967 (to eng H37937E) Commer FC 2266cc petrol 1957-1967
After replacing the water pump don't forget to tighten the centre bolt properly onto the fan. When you have a garage replace it for you, check the bolt yourself.