How tight should a gudgeon pin be in the conrod if its a press fit. I am putting some new pistons on the rods and want to get it wright first time. Thanks Kev.

All the ones, ive done, just press in with your thumb

It should be an interference fit. For example, the Rover V8 gudgeon pins (at least for the BGT V8's) were listed at 0.8745" to 0.8748, and the small end of the rod is listed at 0.8734" to 0.8739". So the fit ranges from .0009" to .0011" .

Depending on the make of the motor, you might be able to find the correct clearances in a workshop manual, failing that, you may want to have a chat with an automotive machine shop.

The Pinto for instance will not push in with your thumb.
An interference fit has to be stronger as there are no circlips in the piston to prevent the gudgeon pin wandering out to the bore walls.
A Pinto needs the con rod little end heated quite hot, inserted into the piston quickly and the pin pressed in with a stop so you don't go to far

If its a fully floating piston rod assembly where the pin is secured into the piston with circlips (or sometimes PTFE buttons) it will push in with your thumb.

If its a press fit as used in newer engines (eg Zetec) you will need to freeze the pin overnight and then heat the little end of the rod. The pin should then simply push in with no need for a press but you need to get it spot on first time, once the rod cools and the pin heats up its there until you use a press and that normally damages the piston.