22 minutes ago, sepulchrave said:

Oil starvation is how that happened, previous owner let the level drop too low and the bearings got starved during braking or cornering when the oil sloshed away from the pickup pipe, big ends have probably had it as well.

It’s as if someone said replace them all while you have the sump off and someone berated them for saying it 

9 minutes ago, thomasaspin said:

It’s as if someone said replace them all while you have the sump off and someone berated them for saying it 

 

Berated is the wrong word and you were GUESSING, the OP has rightly finished inspecting all the mains, I'm now suggesting he inspect the big ends as well.

I'd still only replace the shell that's damaged, none of the others show any signs of wear and if the big ends are all good then it's just the one to be done.

I read that this is a different type of bearing because there was very minimal scoring, almost looks like it's got a coating on it. Is there such thing as red bearings, blue berings or yellow ones? the other half looked identical. Why would this score inside this groove? that should be silver still if that was the case?

How odd, you're quite right it doesn't appear to be worn and if the crank journal is smooth then it must be a different material, I've never come across it before but if the crank's not damaged then you've got away with it and that snapped bolt must've been damaged during manufacture or assembly.

In some bmws apparently they had colour coded bearings having different clearances etc. I didn't find anything related to VAG. I actually reinstalled it as I didn't want to mess with it. It had less wear than the others but that might be because of the colour. 

 

I've inspected the rod bearings and the crank bearings and haven't found any particular damage/wear. 

 

Back to reassembly. 

I have grinded a bearing down to see if it is red and there's no copper there, I think it's just the same metal, I know some are copper with a coating on but this does look to be like that. 

fixed.

This info is decades old so may not be relevant and comes from my experience of building race engines albeit not for many years now.

 

With Vandervell bearings there were two types, the standard white metal over steel bearing caps and the VP prefixed (Vandervell Performance) white metal over a copper alloy over steel shells, these race engine bearings would look identical until the white metal wore sufficient to expose the copper alloy (whose name eludes me) beneath, this was soft enough to continue functioning as a bearing and protect the crank, usually the low oil pressure and noise would precipitate their replacement, the crankshaft journals  would usually be servicable whereas with the standard bearing shells (V prefix???) once through to the steel backing it would trash the crank and often throw a conrod.

 

Often the big ends were the standard shells and the main bearings the copper backed ones, the white metal over the copper backing on the OP's bearing may only have been over the bearing surface and not the oil groove, that could be a modern production cost saving so a worn shell would look reddish all over and a new one grey with a red stripe in the oil groove.

 

The bearing in question does not have an oil groove, surprising for a main bearing, was it perchance the rear bearing with the broken cap?

On 02/10/2022 at 16:47, Bertie90 said:

In some bmws apparently they had colour coded bearings having different clearances etc

 

They are bearings for selective assembly having measured the clearances using plastiguage, the colour coding is always on the back of the sheel where it cannot be worn off.

I wish you could have seen it for yourself. It didn't looked scored that much and the grooves where you fixed the bearing in place were also red, how can it be , why would there be scoring on the side of this wall? To me they looked perfectly fine.