I need to replace the crankshaft oil seal soon on diesel felly truck, so I'm going to put a new cam belt on as well as the current one has done 30k or so. Lots of places such as europarts etc offer a kit and also just the belt. How do I know when I need a whole kit or just the belt? Is it a good idea to renew all of it anyway?

Do the whole lot at once, it's not an expensive kit for those engine anyway.

If you're going to the trouble of replacing the belt, personally I'd apply the kit to help safeguard against future associated problems. Much the same way as combining a water pump change at the same time.

the water pump isn't driven by the cam belt on those, is a seperate external pump driven by the aux belt so it's not so important to do it at the same time, make sure you get a new rocker cover gasket, you need to take the rocker cover off to use the cam locking plate in there when you change the belt, so that is also the ideal time to change the camshaft oil seal too.

Thanks guys, my home car maintenance would be altogether more time consuming, with undoubtedly more cocks ups with out you help! Muchly appreciated.

the water pump isn't driven by the cam belt on those, is a seperate external pump driven by the aux belt so it's not so important to do it at the same time, make sure you get a new rocker cover gasket, you need to take the rocker cover off to use the cam locking plate in there when you change the belt, so that is also the ideal time to change the camshaft oil seal too.

Appreciate that Tom, was just using as comparative example. Quality advice as usual

http://www.lasertools.co.uk/item.aspx?cat=317&item=547

this is the locking set you need, the plate engages with a slot machined into the camshaft, and the pin is for locking the injection pump sprocket..