Big Twin

These heads receive our Stage I Performance Valve Job, 1.850” O.S. Valves, new guides and 7mm conical springs. The head gasket surface will be skim decked to assure a true/flat sealing surface. This is a high quality upgrade for a budget build! Combustion chambers are stock 78 to 83 cc. Processing time Once the cores arrive at Zipper’s they are unboxed, and inspected for shipping damage. Then we review your job order sheet and other related documentation. Job sheets that have not been finalized before your cores arrived will take additional time to sort thru before the job is put into production. Once finalized, the cores will be disassembled, serialized then move into production. Turn around (Process time) varies depending on the time of the season and how long it takes to get your job sheet finalized. Because of the dedicated skilled labor at Zippers and the vast amount of capital equipment we get the work completed with the highest standard of quality with one of the best turnaround time in the industry. Work is performed on your supplied head cores. For our standard production heads Shop Time is approximately 15 business days (during peak season allow for additional time).  The below options will require additional time to process:

• • Custom Modifications
  • Custom Finishes
  • Require Thermal coatings
  • Needing Additional Repairs
  • Or other Non-Standard Work

Exchange heads may be available if the condition of your cores qualifies. The process to determine the condition of your cores is to ship your cores to Zippers for inspection.  

Not legal for sale or use in California on any pollution controlled motor vehicle. Not legal for sale or use on any EPA pollution controlled motor vehicle.

*To ensure you enjoy a premium experience, Please fill out a Build Sheet/Job Order Sheet prior to completing an order on the website. Click here for Zipper's Build Sheet/Job Order Sheet