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Hello ! This is a "motor-head" question ! Can anyone enlighten me as to the purpose of the T-slot which is on the camshaft side of a Willys standard type cast aluminum piston ? I am currently installing a set of NOS Federal-Mogul forged pistons and these do not have the T-slot on them.

They were there to help with piston expansion from the heat.

Thanks Wes ! The forged pistons do not have the T-slot. Is this because they are much stronger and so do not need the slot for expansion ?

Yes I believe the stock piston expansion rate is higher than the new replacements.