[b-man]

Probably the worst thing you can do is use some chemicals in your crankcase to break free a bunch of crud all at once that was fine if left where it was deposited. Clogging up your oil pickup screen and damaging an otherwise okay engine is your reward.

There are products which are formulated to slowly clean up deposits and unstick lifters and such but backyard use whatever comes to mind or happen to have on hand methods are questionable at best.