Hi, With ignition off, feel around cam belt covers, you may well find the belt is somewhat slacker, better still remove the cover to view the belt and tensioner wheel. If the plastic moulding around the outside of the tensioner wheel has torn away then the tension on the belt will have been lost, allowing the belt to jump a tooth or two. Otherwise the belt could have suffered damage (Wear and tear) and jumped on its own accord allowing the valves to be bent by the pistons. If you have tried turning the engine over on the starter motor you may have heard the engine turning over like a fast sewing machine, if so you have lost your compression as a result of a number of bent valves - probably 8 exhausts (From my personal experience, 2.0 Petrol!) My damage was 8 new exhaust valves (guides remained in-tacked and with no cracks - very luckily!) grind in valves and assemble then reset the valve tappet shim clearances (subject to your year/cc/fuel) This could have cost more but it still cost enough with gasket set, head bolts cambelt kit and labour, etc. I strongly suggest you contact the local engine reconditioning shop just outside Oxford, the long established one, see yellow pages. They will help with the head repairs and spares. Good Luck!