my mate has just rebuilt his engine but when trying to start nothing it turns over theres fuel and spark so what could it be?

 

Have you checked for error codes?

Could be many reasons but known MAF sensor to cause starting problems.. try one off another car.

Has the reason for the previous engine dying been found?

If the MAF was faulty the ecu would have learned around it.. as much as it could.. then battery disconnected for a while whilst engine out and therefore resets ECU.. now not use to dead MAF and therefore will not start.

JGM