Loud ticking noise coming from the top of the engine?

First four cylinders are 90 lbs, the last two are 150 lbs compression. There is a loud ticking sound coming from the front top of engine, it isn't misfiring, compression is leaking down though into the crankcase, the engine sat for a few years inside of warehouse, it has 118,000 miles on it. When I first started it there was no noise, after it ran a couple of minutes it started ticking, knocking? It doesn't use oil or smoke any. What could it be?