Andy,
Last april I bought a 48 H that had be running nondetergent oil for all of it's life. I decided to switch it over to 15W40 diesel rated oil, this oil has loads of detergent in it. I pulled the pan and cleaned out lots of nasty sludge, changed the oil filter. After changing the oil I ran the tractor several hours,the oil looked horrible so I changed the oil and filter again. Then did the same about 4 times total. My oil pressure ran ok when cold but would drop kinda low when the engine got warmed up.
After the final time I changed oil the oil pressur dropped to nothing and the engine started knocking. When I pulled the engine down I found no spun bearings, just a crank that looked like it had been running on sandpaper, It needed to be turned to .020 undersized to clean up. The old bearings were Std. size. The babbit material looked as tho it had fine sand impregnated in it.
The mains looked the worst but rod bearings and the cam bearings all had the stuff in them.
I know this engine was due for an overhaul due to lack of compression when I bought it but I feel that the damage to the crank was done by loosening up the sludge and debris throughout the engine.
I'm kicking myself in the hind-end for messing with the oil, but I also wonder if it would have happened anyway?
At least the crank was still turnable. It could have been alot worse!