I'd thoroughly inspect the #4 rod and piston. I bought my sammy with a motor that was thought to have had a rod knock (engine wasn't in vehicle and owner wasn't one who pulled it). So I slapped it back together and there was a tapping towards the back. After a couple of starts I reved it and cured the knock. Of course thats because the rod exploded inside, bent 90 degrees, piston was split in half at the pin. I bought it knowing I was going to put a 1.6 in it so it wasn't a big deal but proabably if I inspected it first I could have saved the engine. I really think the piston is what went first and it went downhill from there. 1.3 is known for the #4 to have problems. When I pulled the engine apart the water jackets around the #4 were clogged with sludge and I believe that it was the lack of cooling that causes premature issues with #4.