What is a core charge?  It is a potentially refundable deposit we use to buy a core of whatever model engine we are building for you.  It is in lieu of you sending us your motor to rebuild.  So:  If you send us your motor in advance, there is no core charge, provided it is in rebuildable form (without sleeving, welding, or other extraordinary measures) as we determine in our reasonable discretion.  If, in contrast, you do not send us your engine in advance, then you have to pay the applicable core charge, then ship your core engine to us within two weeks of receiving your engine build, and if we determine your core to be rebuildable, we will then refund your core charge.  You will not receive a refund of of your core charge if we determine that the core you ship us is not rebuildable without sleeving, welding or other extraordinary measures , as determined in our reasonable discretion.  The amount of the core charge varies by engine model and is stated in the product description for each engine build.