Just picked up a 86 GN that shows to have had an engine rebuild around 6k ago. The engine is smooth and quiet at idle. After driving a minute or two, what sound like a like a lifter starts ticking pretty good and continues as long as the care is above 2 or 3k rpm. After stopping and idling, the ticking slowly goes away. I am assuming a bad lifter, but not sure. Have bought a new set of lifters and plan to replace in a week or two. If it is just one lifter, I would rather replace just the one instead of the whole set to avoid risking a flat cam during break-in. Any ideas/suggestion would be appreciated.