Get it hot and get it hot quickly. The only way to do this without a heat gun is with lean mixture and high RPM. If you understand physics then you will know you are doing it right.

A cylinder will always increase in diameter when heated. Its all to do with Mass, Density and Volume. When a metal is heated it expands thus increasing its volume, Its mass cannot change so the density has to decrease, see formula below


Mass = density * volume
density = mass/volume
volume = mass/density

For the cylinder diameter to get smaller, the metal its made out of would have to be made more dense and thus be colder.

With the different metals in use, the rates of expanding metals are calculated to give the best fit when the engine is at normal opperating temp. I cant say no more so I repeat, Get it hot and get it hot quickly!!!!!!!