Can anyone please give me some advice on the easiest way to replace the water pump on my mx5. The car had cam belt replaced approx 5 years ago by previous owner but now the water pump has started leaking and rattling. Is it possible to replace the pump without removing the cam belt and also would we need any special tools. I appreciate any advice as I really enjoy driving my little car.
Timing belt does need to comes off to replace the water pump I’m afraid to say. Depending on how tight the bottom pulley bolt is depends on whether you’ll need a tool to lock the crankshaft to undo it. As a general rule, I find selecting 4th and applying the parking brake holds the crank firm enough to undo the bolt. The same technique can be used for re-torquing it.
After 5 years I’d do a full cam belt replacement (pullys ect) with the water pump anyway, its not expensive and easy to change yourself, normally people change the water pump when they do the cam belt so they don’t get the issue you now have, people forget the cam belts go with time not just miles and some people don’t bother as its not a interference engine but you can be sure when one does brake it will always be at the worst time in the worst place possible and don’t forget its probably quicker to do the belt than wait for the AA or RAC and you then still have to do it anyway 
sorry to sound like your mum/dad
Thank you so much for your replies and tips. It looks like the most sensible thing to do is replace the cam belt as well. Big job but it will keep my car alive for a bit longer.
Hi, we replaced the pump without incident (apart from snapping one of the bolts) we put on the new cam belt checked all the settings but after turning the crank the settings were all out. The belt didn’t slip so we’re at a loss to what’s wrong. Can you help again please?
Did you lock the cams before you took the belt off.
Cams weren’t locked but the timing marks were all in the right position and crank key was at the top. Rain stopped play today but we removed spark plug one to confirm crank in tdc position with key at top on pulley. If inlet and exhaust cam pulleys are positioned properly with I and e at 12 o clock should the timing be right?
That depends on which I & E you are looking at. Each of the camwheels has an I & E on it, but as you look at it from the front, the left wheel should have the I to the top but more importantly its E should line up with the mark on the metal plate inbetween the camwheels.
Have a look at this How To:
http://www.mx5modsters.co.uk/forum/viewtopic.php?f=89&t=3123
You need to lock the camshafts together with a selection of openend spanners and adjustable grips as they will move about.
I would not recommend this job to anyone who has not done a good bit of spannering.