my cosworth is eating up the alternator/water pump belt like its goin out of fashion.. i've replaced them 3 times and they're only lasting a few hundred miles at a time. i've checked theres no marks/damage to the pulleys and the alternator and water pump both run free turning them by hand...... its the 2wd set up with the V groove twin belt set up

 

is there any movement in the belts to look at when running? with throttle applied etc

 

no the belts look tight when its running and rev'd

 

Be more specific with the description of lasting, what is happening snapping, stretching, squealing, etc etc.
Check the pulleys are lined up 100%, you will be able to see this by the wear pattern on the pulley being the same each side of the V.
tabetha

 

right, the belts start to squeal, and go thin at the sides then and snap, i had the tension checked the last time by my local garage and they said it was fine, 2 days later belt squeals then is broken within no time atall

 

hi sounds to me that the pulleys are worn the actual v's are worn at the sides and are more like u's this allows the belts to run on the top edges and therefore wearing them out too quickly, could be wrong but in air conditioning and ventilation systems this is a symptom of worn pulleys, may not be all the pulleys but check each one for wear and change the one you find to be worn,
also when you get belts make sure they are a matched set or at least as identical as you can, even though the numbers are the same the belts will be different sizes
john

 

ok i'll have a look at that thanks

 

The point about matched belts is a good point, sets I buy are often different even from the same supplier/maker, only a slight difference but enough.
I suspect that something is partially seized/seizing, almost definitely the alternator bearing, does this feel nice and free with no roughness, we know the crank isn't seized or the water pump(but check this also), if too much force is needing to be transmitted through the belts they can do what is happening.
Next time it squeels, stop and take belts off and check alt and water pump.
tabetha

 

ok i'll give that a try, alternator is definatly free, water pump feels free by hand but i wouldnt say it was just that free it would easily spin, however the car always runs super cool, rarely goes above m on the temp guage

 

on the belts point, when you have a pulley with more than one belt if you have belts that are even slightly out size wise, the slackest belt will usually, after it has run in, slip, then acting like sandpaper will wear the sides of the pulley where it sits rapidly,I have seen this happen on new sets of pulleys and belts then been sent back within a day or two to find the pulleys gone again, and also you tighten the belts more to take up the slack in the bigger belt and again it knackers the bearings,
just more dribble
I HAVE MORE!!

 

Anything binding might be doing it mostly when hot, though alternators with stiff bearings are worst normally a minute or two after starting.
Let us know how you get on anyway, could help others, thanks.
tabetha

 

yea i'll defiantly do that, thanks for all your help people

 

my power staring belt does this