im guessing this main bearing is about shagged?

[pongo]

not sure of what to make of it. has good oil pressure,etc. supposed to be a fresh rebuilt motor ,etc.

still looks/feels round but i dont really know what im looking for.

is the bottom rear main shell on a SD33T. 3.3 turbo diesel MQ patrol

[Z()LTAN]

The shiny bit in the middle looks like normal bearing face whereas the sides look worn.

Id say the crank tunnel is out of round.

[WRXZook]

I wonder if the nip and crush was checked/set up in the rebuild? Or not cleaned properly before the bearing shell was fitted?

[shortyq]

that bearing has been starved at some point!
either on startup,or offroad perhaps!

[Dirty]

That bearing is worn. Could either be because of oil starving or from a lot of use. The middle bit looks like the top coating of the bearing has been removed and there is also some additional heavy wear in the middle.

It looks like normal wear and ready for a replace, but others on here might be better to identify oil starving issues I have never experienced that to the extent that it has worn/damaged bearings.

- David.

[Ruffy]

that bearing has been starved at some point!
either on startup,or offroad perhaps!

Are you for real???????

[shortyq]

that bearing has been starved at some point!
either on startup,or offroad perhaps!

Are you for real???????

get all tech n shit!read the authors post!

[pongo]

interesting reply guys. love for some more people to follow up. Iv had this motor for a few years now and has always had fresh castrol RX super oil but sometimes cheap oil filters. always done at 5k and nearly all hway kms.

Maybe its time to fit a real oil pressure gauge instead of nissans factory job to really keep an eye on things. perhaps it didnt like all the midnight express runs down the hume, i used to do a few years ago.

did notice last time i had the rocker cover off it was fairly sludgy. have found out that oil samples cost about $30 to get done inc postage,etc. Definitely need to keep an eye on things i think.

any more ideas keep em coming. was too scared to remove the rest of the caps to have a look.

[Ruffy]

There's nothing wrong with it.. Pull the rest of them off..
It looks just like a babbitt coated bearing would after being used.

Check the back of the bearing. if it's purple it's been hot. if it's blackish or clean it's good.

Are there any discernable marks or scores on the crank?

[date]

You don't say (maybe don't know) how many km the engine has done since its rebuild. Whatever, the shiny bit in the centre of the bearing shell would be a slightly worn bit and if you could measure the radius of that area, you would find it to be close to the radius of the shaft journal. The shaft has a slighlty smaller radius than the bearing and you can see that effect in the photo. This is normal.

It looks as if the original white metal of the bearing shell insert is still there, so I wouldn't be too worried about it. You will probably find the other main bearing shells are in similar condition. I would replace the set whilst the engine is stripped down anyway.

You mention getting a new oil pressure gauge. I wouldn't bother. Oil pressure is only used to ensure circulation of the oil through the engine. Sure, if you have a worn bearing, all the oil will escape out that spot and then tend to starve the rest of the bearings of oil. The principle of oil lubrication is that a thin wedge of oil is built up as the shaft rotates. The oil is dragged into the wedge by the viscosity of the oil, and then forced out through the thin gap between the shaft and the bearing shell. The thicker the oil, the better the wedge - up to a point. The oil gets hot in the close clearances and this is probably the main reason for having an oil pump - to provide plenty of fresh oil where and when it is needed. The pressures built up in the wedge are very high - thousands of psi - way above the pressure developed by the oil pump.

You only have to look at any old engine eg Model A fords - most of them used splash lubrication for the bearings. They didn't even have an oil pump. Modern Briggs & Stratten engines still use splash lubrication. Large machinery eg large pumps and turbines use high pressure oil for startup to ensure that oil gets under the bearing, but once it is up and running the HP oil is often cut out and only cuts in again as the unit shuts down. Once a film has been established, it is self sustaining, given an adequate supply of fresh oil.

The material used for the bearing varies, but is generally a soft metal. It is designed to be sacrificial ie it is designed to wipe and fail without (hopefully) damaging the shaft. Indeed, often the new bearing slippers have a flash of a very soft metal eg indium to assist in bedding the new bearing into service. If the crankshaft journal is not scored or scratched, then I would have no fears in putting in a new set of slippers and running it for another XXXXXX km.

[pongo]

too easy. I had it out as i was doing the rear main seal. Didnt check the rest as i dont like touching things that seem to be ok for fcedar of rooting em properly. Engine prob has done 100 thou since the alleged rebuild. No scores on the crank that i could see.

Have bung it all back together so time will tell i guess.

cheers

[SIMMO84]

As others have stated the bearing is fine, by looking at that one I would guess the top bigend bearings will be showing brass which is also ok. Just means that it will loose some oil pressure but nothing to worry about.