Hi
Assuming you're intended to use the 'interim' timing cover with crank driven oil pump and a dizzy, etc? The centre of the pump is about the same as for the P6 version. Maybe very slightly lower but not by any significant amount. The problems I have had with the conversion (which was not done by me, and was not completed because I think the guy who attempted it - supposedly a P6 expert - just ran out of ideas, and why I am converting back to P6 spec) are these:
1. Unlike the P6 water pump the serpentine pump needs to spin anti-clockwise. As you know the crank spins clockwise (when facing the engine from the front) so this means the belt needs to go under the water pump pulley (which is smooth-faced, to match the smooth, reverse side, of the belt). To achieve this (and maybe for other reasons) Rover put the PAS pump up high, top front on the nearside (left side) of the engine, giving the belt a route upwards from the crank and then back down to the water pump, and then up to the alternator on the other side before dropping back to the crank. (Ignoring any idler/tensioner pulleys or AC pump pulleys of course). On the serpentine PAS bracket, and using the serpentine PAS pulley (which is quite wide) this pushes the belt up, making it rub against the underside of the top radiator hose. To overcome this I modified a Skoda water pump pulley. It has the right centre hole and the right number of ridges, and the right front to back dimension, but a smaller diameter than the Rover version, which just about drops the belt below the hose. (You need to drill three new fixing bolt holes in the Skoda pulley but its only made of plastic so this is no big deal.) Great, but now the PAS pump also gets in the way of the engine steady bar; if its fitted (as Rover did, between the PAS pump bracket and the engine) this pushes the PAS pump too far forward, out of alignment with the crank pulley. It's probably possible to cure this by grinding some metal off the back of PAS pump bracket, which is only alloy, but I haven't gone that far. A different pulley would be another solution but I think you'd have to have one made.
I also worried a bit, perhaps unduly, about the effect of spinning the PAS pump faster than it was designed to spin. This probably doesn't matter on the basis that there must be some sort of pressure relief valve arrangement in there? I have no idea.
2. Unlike the P6 version the serpentine water pumps (I've checked them all, although there might be an old Buick or whatever version that has escaped my researches) have no outlets for the cabin heater hose, and unlike the P6 version the back of the timing cover has no outlet for the thermostat bypass hose. When I got the car the P6 'expert' had not solved these problems. To overcome this I put a T connector in the bottom radiator hose, and another smaller T-connector off that, to plumb in the two hoses. It actually worked quite well, but looked a right bodge. There are probably other ways of curing this problem, - perhaps involving using a heater hose as a thermostat bypass? - but I haven't explored them. I'm no expert and I decided I was getting in too deep at this point.
3. The interim serpentine timing cover has only one port for the oil pressure sender and oil warning light - which isn't the right thread for a P6 pressure sender or oil warning light switch. I solved this by finding a suitably threaded T adapter, allowing me to plumb in both the sender and switch, which works fine, but again it looks like a bodge.
4. Tensioning the belt is a rigmarole. To be fair I found it actually needs no more tension than a V belt. This sort of makes sense on the basis that one of the advantages of a serpentine belt is its width and its multi-ridges, which makes for a lot of friction; massive tension is not required. (I did experiment with a tensioner/idler but decided the level of tension it created was much more than required.) I found the best way of tensioning it was by levering up the alternator in the old-fashioned way - but it wasn't easy creating arrangements to mount and fix the alternator to allow this, using the new timing cover. There are other solutions to the one I tried, including perhaps the Land Rover thing of a screw tensioner across the front of the engine? - I didn't get that far.
5. This was the killer for me: The serpentine water pump is really designed for a screw on viscous fan with the 11-blade plastic fan. (30m metric fine thread.) I even bought one. However, the pump is just too long to allow space for the fan and its viscous adapter. I tried to overcome this by doing away with the viscous and just bolting the fan direct to the pump, but this required me brazing up an adapter. A 30m trailer hub nut was the best I could find, brazed to an aluminium plate. Again, a right old bodge, and creating clearance at the back for the pump pushed the fan very close to the radiator (we are talking a few mm, although my radiator has a slightly thicker core than standard) to the extent that it rubbed the underside of the metal fan shroud. I could maybe have solved this by finding a smaller fan, or adapting in some way the old metal fan, or shaving the tips off the plastic fan, but at this point I threw in the towel.
It's all soluble, no doubt, but needs more skill and knowledge than I posses - a low bar! I managed to get it all working (but no fan) and decided I couldn't live with it. The advantage of a crank-driven oil pump and a single, easy to change, belt, just didn't seem worth the disadvantages. Maybe if it was to facilitate an aircon installation it would make more sense? I would love to hear about a successful conversion. I also have a P5b with a serpentine front (currently off the road) and it is much better, simply because there is far more room to play with than there is in the P6.
Best wishes
Andy
