Before you tear into the engine consider a supplement that claims to free sticky lifters. For about five bucks it's probably worth a shot.

Another alternative is to use a HD diesel engine oil (API service categorty CI-4) like Chevron Delo, Shell Rotella, or Mobil Delvac. These oils have a higher dose of detergent additive than oils blended for spark igntion engines (API SL) and have been reported to free sticky rings and lifters.

The common multi-viscosity grade for these oils is 15W-40.

If a lifter taps all the time its probably collapsed and needs to be replaced. If it only taps mostly when cold, it's probably partially clogged and might free up with a heavy dose of detergent.

Duke