| Casting defect | Cause | Improvement measures |
| Increase or decrease in outer diameter | The external mold shrinks and deforms, the direction of the cavity pin hole increases, the direction of the pouring riser decreases, the mold closing gap increases, the lock is not tight, and the pouring aluminum leaks; For the poured piston, the center line of the pin hole is not perpendicular to the parting surface, resulting in the increase of the horizontal wall thickness difference of the pin hole. | Scrapping of external mold |
| Inner diameter increase | The positioning pin and core neck of the external mold are worn, the core assembly is loose, and the contact gap increases; The external mold is not locked during mold closing. | The neck of the core and the assembly surface shall be cleaned, the core shall be in close contact, and the mold shall be closed and locked. |
| Pin hole seat spacing increases | The positioning pin and core neck of the external mold are worn, the core assembly is loose, and the contact gap increases; The external mold is not locked during mold closing. | The neck of the core and the assembly surface shall be cleaned, the core shall be in close contact, and the mold shall be closed and locked. |
| The outer circumference of the pin hole seat is large | Low temperature of molten aluminum; Poor ventilation of copper plug; | Replace the vent plug and raise the temperature of molten aluminum appropriately; |
| Reduction of lumen depth | The middle core mold is lifted and not lowered to the bottom | Straightening external mold locating pin |
| Increase of top wall thickness | The core mold is not down to the bottom, and the thickness of the covering seam of the mold base is large | Straighten the locating pin of the outer mold; Correct the levelness of the base |
