Aztman If your changing the rod i would also reccomend the wrist pin, the wrist pin cost about $4 and replacing it will mean that the entire assembly is brand new.

Vti, a broken in Go engine runs its best between 220f-230f, if you try to put a race tune on a go engine before its fully broken in (less than 1-1.5 gallons, they have a lot of pinch) it will run in the 260f range due to excess friction due to pinch.

kenshinmd, jpz is right use a heat gun and the added head shim. Break in varies from person to person, I think your best bet is to go to a track and have someone help you break in the engine, If not you can check the Racefactorindustries.com website there is a break in method there that is pretty popular, it can be done on the ground or on the box, doing it on the ground is a little better.

JPz what engine are you planning to throw in that 5t, the .25 6port is pretty wicked in a truggy.