The scribe lines on the RV-14 cowl are accurate and valuable for saving a novice builder a bunch of time when starting the initial, trimming while doing a cowl installation.
They designed to trim the cowl enough that it can be fit into place, nested on the attache hinges and fitted behind the spinner, but not with the proper spinner gap. This is to allow for slight variations between each installation, trim error, etc.
If the builder follows the instructions, it will lead them through the process of initial trim to get the cowl quickly to a point it can be roughly fit in place, and then take measurements for the small amount of trimming required at the back to move it aft and achieve the proper spinner to cowl gap.
It is important to correctly position the rear spinner bulkhead on the prop hub and confirm that the bulkhead is flat and of equal distance to the ring gear support around its perimeter (detailed in the RV-14 spinner installation instructions).
Any opinions expressed in this message are my own and not necessarily those of my employer.
RV-6A (aka "Junkyard Special ")