UK Ford Repair Questions? Ask a Mechanic for Answers ASAP
I am afraid there is no definitive answer.
The culprit can be determined only by stripping the engine.
An experienced mechanics ear can narrow down the problem by using listening devices but again its not guaranteed.
You can establish if one or the other has suffered damage by draining the oil, removing the sump and looking for swarf which will have been removed from the bearing shells and captured in the oil/pick up pipe/sump pan.
If there is evidence of metal in the oil removing the camshafts will be quicker and easier than trying to get to the con rods.
If the noise is definitely present I would seriously consider stopping driving immediately because if the bearing fails completely this will cause some serious damage.
At the moment you replacement parts will be negligible in cost as bearings and replacement gaskets are relatively cheap and it is the labour cost which will take up the majority of the bill.. However if you continue to drive and the bearing fails completely then you could end up needing a complete engine as the big end failures can be very damaging.
If you need any further information just get back to me
All the best