330 runs hot now

[GOTFEAR]

I have a 330 pv esr cylinder on first bore for a bout 1 year runs great but now runs hot i raced a big race with a lot of top end and ran it a little lean melted the top of the piston and no damage on the bore replaced piston and clutch cover with a good water pump and runs hot after 2 laps. blows coolant out the overflow not the ex pipe ???????? what do i do

[norcalduner]

Try pressure testing the radiator cap and see if it is holding pressure.

[Aceman]

I'd check for bubbles in the radiator indicating a head gasket leak.

[GOTFEAR]

will do

[C-LEIGH RACING]

When you presure wash the bike, do you wash back through the radiator fins to clean out the silt & mud built up in them.

Over time those fins can get clogged up at the bottom & no air can flow through them to cool the fluid.

Signs for a leaking head gasket or o ring, with the radiator cap off, when you rev the engine some, the coolant will be real agitated + bubbles as already noted, not a smooth flow.
Neil