erm... just a bit

parts alone are about 200-300quid (inc. ford staff discount) and to change em you have to take the heads off (so budget about abother 200quid in gaskets, bolts etc. etc.

then theres the labour to dismantle the engine, fit the new chain+tensioners+guides etc. and then re-assemle

not forgetting the things that are likely to break when disturbed, maybe awaterpump or a thermostat housing or something more simple that'll need replacing.

so yes, its not a cheap job to get done

works out cheaper to replace the entire engine when i it breaks than it is to do the preventative manitenance in the 1st place :P

somebody who wanted to be extra extra sure would buy a 2nd engine, and rebuilt it properly and to a bigger spec inclusig all new bits that need to be new (like timing chains) and then fit this new engine when its all complete