Not familiar with Leo's, but if it has a taper bore. i.e. tho top of he cylinder bore is slightly smaller than the rest of the cylinder to give a more precise piston to cylinder fit at TDC, the pinch should be felt even with the plug out. With the plug in, it will be even tighter as the extra compression is felt.

The clicking may be the connecting crank pin and rod bearing that is common with many of todays engines like OS, Magnum and the like that have the tapered bore. This will occur at TDC. The piston is tight at the top and as the crank comes off TDC and any slack in the pin and rod bearing will be heard. Some clearance is required to allow the lubricant to do its job. This is known as oil clearance.

To make sure that the piston is not striking the glow plug, measure the depth from top of piston at TDC to the outside top of the plug hole. With a depth gage or use a small plastic straw inserted in the glow plug hole. Make a mark where the top of the hole of the glow plug is and then compare this length to the glow plug's threaded portion. Make measurements with the copper washer removed. Another method is to place a small dab of grease, vaseline, etc. on the base of the plug and let it extend about .5 mm. Then place the plug in engine, and rotate the crank. Remove the plug and check the grease for any indication of contact.

I have several brand new engines, OS, Magnum, TT, and they were so tight that I could not turn them over by hand unless I had a prop on the engine. Once I broke them in, they were still tight but I could turn them over. I can hear the clicking just as the piston begins to come off TDC. Make sure you dont use synthetic to break the motor in. Syn. is very slick, as it is supposed to be, and will take for ever to break in the engine.