2003 Polaris ATV Trail Boss 330 Factory Service Manual, Page 61Get this manual
CYLINDER HEAD WARPAGE
1Lay straight edge across the surface of the cylinderhead at several different points and measure warpage by inserting feeler gauge between the straight edge and the cylinder head surfaceIf warpage exceeds the service limit, replace the cylinder head
2Remove spring retainer and spring
NOTE: The valve springs should be positioned with the tightly wound coils against the cylinder head on progressively wound springs (A)3Push valve out, keeping it in order for reassembly in the same guide4Measure free length of spring with Vernier caliper, Ill.1Check spring for squareness as shown in Ill.2Compare to specificationsReplace spring if either measurement is out of specification