Cannondaleriders

i have a buddy that has a 400 ex, he sent the motor to a the local napa machine shop to have a 440 kit put in it, he got a brand new head, new titanum vales and springs, when he got it back it ran fine for about 45 min and then it blew a head gasket, and if it runs for about 10 min it will blow a head gasket or the spark plug, any ideas what wrong with this p.o.s honda? thanks for the help

The big bore sleeve moved up or down. Mill the surface down a few thousandths. Also, to check, move your finger nail over the cylinder surface and the sleeve surface.