Just picked up a non running 448(backfires only) for a really good price. Haven't had time to get into it yet but it has a horrific screeching sound when the starter is engaged. Originally assumed the starter/flywheel ring or internal damage was the cause and was why the price was right on the tractor package. This machine also has oil accumulated in the air filter housing and on top of the block (but more on this later). Poking around the engine compartment I saw that the pto clutch assembly is pushed into the screen by at least 1/4-1/2" whereas on one of my other 448's there is around 1/4" clearance between back of pto clutch hub and the front of the screen,maybe get lucky and is just sheet metal interference. Also, regarding the oil in the air filter could be caused by the broken reed valve spring, chunk of it is missing and torn gaskets for the cover plates. Is there a spec for the length of the reed valve spring as I have a couple of boxes of compression springs and would probably have something that would work. Always an interesting gamble buying these old tractors, never really sure what you are going to end up with.