What is the difference between standard size main bearing and oversize main bearing. Which is best for the 5.4L V8 engine

You can take the bearing shells to a bearings specialist, or you can have the crankshaft metal sprayed and reground to standard size.

you will not get oversize bearings for big ends and mains
you will get .010" undersize bearings if the shaft has been ground .010"
get them from any engine reconditioning shop or good auto spares retailer

This phenomenon is called blow by. This usually happens when the engine compression escapes through the worn out piston rings due to the severely scratched cylinder wall. It also happens after the engine becomes severely overheated due to the loss of coolant or the car is driven with ruptured element air cleaner for longer period of time or due to the aging factor.
In this case the engine requires complete overhaul. It includes the replacement of the following parts to help enable the engine to perform satisfactorily as long as for many years without any problem.
The dire requirement here is to maintain the oil clearances of various parts during the machining process to ensure the reliability and dependability of the engine.
Engine parts to be replaced with original:
- Engine valves.
- Valve guides,
- Piston set (oversize).
- Ring set (oversize).
- Main and big end bearing shell set (Oversize).
- Crankshaft thrust (oversize).
- Timing belt and bearing set.
- Gasket set complete kit.
- Oil filter.
- Element air cleaner.
- Engine oil.
- Silicone RTV Grey.
- Radiator coolant.
Machining:
- New valves and guides fitting and valve seat redressing.
- Valve clearance adjustment.
- Cylinder re-boring and honing.
- Crankshaft grinding, main and big end bearings fitting, and main line checking/ correction.
- Connecting rod alignment.
- Radiator cleaning and cooling system inspection.
Hope that works.
Thanks for visiting Fixya.

These are really helpful, but do you guys know whats the standard size journals sizes would be on main and big end? idk if anyone would answer as last person replayed back in 2011 lol

May just need to adjust valves. Not sure about your oversized rings, if needed oversize should have been bored out for new pistons.

Switch to a different grade oil. (20W50 if you're not on it already). If this does not change the symptoms(and I doubt it would) the main bearings are worn. (Despite what you read about testing the pressure switch, they rarely fail)
With bearing failure, depending on your budget, you can :

• Change main and big-end bearings
• Rebuild the complete engine
• Replace the engine with a factory rebuilt unit

Replacing with something from a breakers yard is gambling as you never really know what you get. If you're under 150000 miles (erm... the car I mean) I'd recommend having the crank resized and fitting oversize bearings which is the most cost effective DIY option. You'll need to remove the engine. Remove the sump, damper pulley, clutch/flex plate and finally the crankshaft. Everything else on the engine can remain intact. You'l need to take the crank to an engineering shop to have it resized. Once done they will give you the new sizes or perhaps they can supply you with the new bearings. In order to do this get a good quality repair manual (Haynes or Bentley- avoid Chiltons) or you can post here again.

When you order bearings they list them as standard or .005 oversize or .010 oversize and so on. If you are ordering a new crank it should require standard bearings. And alot of times new crankshafts come with bearings.

To do that properly you will have to pull the motor out, remove crank, check to see if you need standard or oversized bearings and do all new gaskets.

It has happened to me that, when ordering parts, i was given .025 oversized bearings after ordering standards. take it back apart, and double check the bearing marks. if they are what you ordered, use some micrometers or plastigage, and get the correct set.