Jahn's Cast Piston Clearance

Does anyone know what the clearance is supposed to be on these? They are FE 406 pistons, 0.030" over (4.19" bore)

It seems that I remember reading somewhere that it could be as high as 0.005"-0.008" clearance for the cast pistons because they were such heavy and thick castings since steel re-enforcements were not used like most other cast pistons.

Thanks,
Roger

 

When i get a piston with no info on it at all ,i measure it then sit it on a hot plate untill about 200 deg and remesure adding in a thou or two for oil.

 

Gary,

That is a good idea, I have never thought of that.

However, don't most pistons run at a temp of around 500-600° F? If, 500-600° F is the operating range, then would that not be better to measure them at. You could do this in a regular oven since you can easily get an oven to go up to 500° F.

Thanks,
Roger

 

Over 300 the heat trating if any is lost,the piston will be like penut****er. piston running temps are well below that. combustion chamber temps are another story .
If you look at the bottom of a used piston the oil is baked a golden brown(med heat) if it was at 500 you will see black chared oil