Main and thrust Bearings
page is incomplete
Two bearings shells come together to make one journal surface. Two of these have the thrust surface on them and those two parts must be in alignment. If you wish to change rod or main bearings with the crankshaft still in the car and don't wish to pull your engine see this link: Main Bearings This would be a good idea to do if you don't have to time or money for a complete rebuild or the equipment to pull your engine.
The main caps in the block have oversized holes in them and your bolts have a shoulder at the head. The shoulder is still smaller in diameter than the the opening in the cap. All the caps can slide front/back on the block surface and still provide a bearing surface for the crank journal but the one with the thrust bearing must be aligned front-back to the loading surface of the crankshaft.
All main caps have an angle cut on the outer tips.
Put the insert into the cap locating the lock tab so it seats properly. Fully grooved inserts go into the block and may have larger oil feed holes in them compared to the other insert that goes into the cap. Place the cap on the block and using your fingers put in the two bolts and hand tighten them. Using a plastic hammer or suitable substitute tap the cap down to seat it to the block then again hand tighten the bolts.
If you can't turn the bolts with your fingers then the cap is too far forward, rearward, tilted or is twisted. Loosen the bolts and look at the gap around the bolts in the cap and correct the alignment. You can tap the cap to align it. Finger tighten again then put a small torque load on the bolts. Alternate the torque loading then finish in stages to the factory spec. of 55-61ftlbs.
#3 main cap also has the thrust bearing. Put this cap on in the same way then after you have put on a small load on the bolts, say 10ftlbs to be sure the cap was seated then just loosen the bolts. Now gently tap this cap rearward toward the flywheel then again finger tighten the bolts. Tap at the middle or lowest part of the cap so not to just tilt the cap only to have it stand back up and end up doing nothing. Using a pry bar, push/force the crankshaft forward to help align the two thrust surfaces in the upper and lower shells then put a small torque load on the two bolts while holding the crankshaft in this forward position. Turn the bolts down in stages to their final torque load. This should result in an even, greater thrust surface to better carry the load because the faces of the block and cap are aligned. This is what the cap has for a "range" of movement so you can see how this could be easily installed wrong if you do not set the cap up as described.
This cap must be in alignment for the bearing to be in alignment but you can't see this after the crankshaft is installed.
For this #3 cap, ignore where the cap is in contact with the block, what matters on this one is where the cut away portion lines up to the block where the thrust surface is fitted. This cap could be installed incorrectly to far forward or rearward and you be in spec for the end play but you may only have one half the thrust surface area. As that half thrust surface amount is worn away much quicker that makes for greater overall end play as the two mating thrust surfaces wear to be flush with each other.
Bearings and crankshaft in, the cap pushed rearward below left, the cap moved into alignment below right
With all the main caps on and all the bolts torqued down you can measure the end gap. Put a pointer of sorts on the block and point over to the crankshaft. Now pry the crankshaft forward - rearward and measure that distance of movement you observe at your pointer. Factory spec. of this "end play" .002-.0071"
(flywheel "run out" is something different, it tells is the flywheel is properly seated to the crankshaft surface so it will not wobble)
If you do not finger tighten the caps then tap them down and you let the bolts PULL the caps down the insert could move, the insert could come out of the cap enough for the lock tab to come out then be forced into a position that damages it. The cap could go on twisted or have one end not drop down to the block surface. You could even bend one of the bolts.
This is a failed #3 bearing from a cap that was installed incorrectly and the bolt is bent near the head. This was a poorly assembled engine and likely it was this bolt that pulled the cap into position and it bent as a result of the torque applied to it. Its hard to tell but the lower bolt is the bent one. It wobbles when screwed into the block and cap. This bolt is ruined.
Here's what a thrust bearing looks like after improper installation of a #3 main cap from the bent bolt shown above. The material that was chewed from the main bearing passes through the the rod bearings on 1,2,4 &5 but do not on the #3 as it just feeds the thrust surfaces. After the debris that damages the main bearings that is too large to embed into the bearing surface is passed to the rod bearings and causes further damage. Two of the wrist pin oiling holes in the connecting rods of this engine were clogged with bearing material. This small piece of bearing material shown next to a quarter come one of the other main bearings as #3 doesn't feed oil to a rod bearing. The piece of bearing material scored into the rod bearing then passed into the wrist pin oiling hole in the rod and clogged it. The wrist pin on that piston was binding.
Someone had "rebuilt" this motor. I'd rather say they just put a short fuse on it, put a match to it and walked away because I doubt it ran for long but these aren't severe enough to cause knocking. This motor had one other thing done that would have caused it to have eventually failed and that was that this particular brand of main bearing inserts have smaller holes in one half, the markings on the back were "F/m" The pieces of debris that stick into a bearing surface rather than embed into the surface will result in greater crankshaft journal damage. The smaller specks in the bearing surfaces here are or were embedded debris. The lines were caused from debris that both scored these bearings but also the crank journal. Remember main bearings feed rod bearings with the exception of #3 so if it scores a main it will likely also score a rod.
You can actually have copper/lead bearings that have the lead worn away and the copper visible and the crank journals only have minor wear. Such minor wear can often be just polished out of a hardened crankshaft but will usually ruin a non-hardened one.
It has in the past been stated that the design of the oil filter adapter on a turbo version G54B engine doesn't at 100% of the time filter the oil. This is not true. The oil passes into the filter 100% of the time and its the first thing to get all the output of the oil pump. Sometimes the oil is bypassed to the oil cooler but it still must pass through the oil filter. You will have oil that is bypassed and as a result of that the oil will be unfiltered but that is a result of something that occurs in the OIL FILTER not by any design of the lubrication system. Oil filters have a bypass in them to prevent them from failing in the event of an over pressurization situation or clogging. Some times with cold temperatures and oil that is of a thicker grade then recommended for the temperature zone may be of a consistency to not back able to pass through the filter and as a result your 20w50 you run in the winter you picked to gain you that extra "pressure" you see on your gauge is actually worse because it all can't be filtered. Didn't think about that did you? Any debris you have in the oil that isn't filtered isn't helping you it is causing damage. The oil pump in this engine starts dumping excess pressure when its nearing 3000rpms and anything over that it bypasses some oil back into the sump. High detergent oils at high rpms is not good for reducing "foaming". Oil with air bubbles in it will result in an oil starved engine. Synthetic oils generally have a higher temperature range to continue to remain as a lubricant. There are synthetic oils from Royal Purple and Red Line that have levels of additives and detergents to help reduce foaming and are good at handling the heat from turbo engines. Do not break in a new engine with synthetic oil.