Piston - Cylinder Clearance Theory

Please forgive me if this has been discussed and I did not find it but my question is as follows.

With some pistons it is mentioned that they sometimes require measurements to be taken at a specific temperature. Most of my work is in a not well conditioned shop and the temperature is usually, on average, around mid 70 to mid 80 degrees Fahrenheit. Could someone assist me with the theory/reasoning behind checking measurements at a certain temperature as opposed to checking the measurements and clearances in conditions that the parts and engine will be in at all other times (except for during engine operation obviously).

Hopefully that all makes sense, thank you all in advance for your help.

The materials that are used for making pistons are well known in terms of their properties including thermal expansion. That includes thermal expansion at different temperature range. Manufacturer knows exactly how much the piston is going to expand at room temperature as well as how much it's going to expand inside the engine at normal operating temperature as these two numbers are directly related via temperature expansion coefficient. So if manufacturer states that at room temperature piston has to have A piston to wall clearance it means that it will have B piston to wall clearance when hot inside of the engine - that B clearance is optimal for that piston size and material it's made of and that's what manufacturer wants you to use for best reliability/performance/longevity...

Is that what you were asking about?

I think I understand now thank you! So it's just a reference temperature and clearance to ensure that the proper clearance will be there when it does expand at normal operating temperature.

That makes sense now. Thank you very much!

Yes, you are 100 percent correct...