I've found that my "Cajun cooker", water, and dishwasher detergent works very well. And smells good too. Just set yer parts "stew" boiling, and go do something else, like hone cylinders, or something.
Also, a good used dishwasher works just as well, if not better. Just put yer parts in and turn it on.
(Don't use the one in yer kitchen, yer Ol' Lady will get mad) Won't damage any soft metal parts, and get's 'em nice and clean.