Petrol engines 2.1 Throwing a rod
HarryMann: 2.1's can and do run big-ends and can throw a rod
Lots of oil everywhere and a hole in the top of the crankcase gives good witness to this occurrence. Not that common, but on longer journeys, with high mileage 2.1s, hot or low pressure oil doesn't help - they can throw a rod! In the USA, with their very long distances, hot weather (thin oil) and heavy loads, this is a more frequent occurrence than here and sometimes just comes out of the blue.
The bolts stretch, a journal ovalises, the stresses go up, something gives... you won't have a lot of warning usually. More likely if you've been running a low pressure buzzer, or stressing it on the motorway on hills or into wind, but if its time is up, it'll blow.
Laurie: (Laurie-Pettit-Engines) says the following on this subject
The water boxer is particularly nasty with big ends because you don't always hear that they've gone!
I recently had a mate wanting me to do his head seals and I found a couple of rusted studs. This meant that I had to strip the engine right down and found that one big-end was badly worn (0.15mm loose!). I made him come and see the engine before I carried on with it and he couldn't believe it because there had been no knocks or rattles.
The other thing is to keep an eye on the end float! Once the outer thrust wears, the oil just sprays out of the rear main. So one way of securing the bottom end is to deal with end float quickly (which is really easy to do on the late boxer engines).