I had a flat head Ford that set for years with out running. To clean it, I filled the whole engine with Castrol degreaser and let it set for about 1 hour. I then drained it and used it on the out side for more cleaning. Then using a very hot, almost steam, pressure washer, sprayed inside and out till the soapy water ran clean. I never pulled the pan or any sheet metal. It took about a hour of washing to clean, but the results were worth it. The oil stayed like new after that and is still clean now. Using extra hot water was the key, the engine dried almost immediately after washing due to the extra high heat. I added oil right after washing and rolled the engine around to coat the inside ( it was on a hoist).
I have washed a few engines this way with out problems. The key is to use strong soap, really hot water, and get oil in it right away.
Engines are a lot tougher then people think, they will take almost anything you through at them. Don't be afraid to get in there and really scrub and scrape. Pull the pan and check before and after, you will know if its going to live or not by whats in the sump.
Joe
