Guys and in reverse order
The 4200 is actually a Ferrari design developed by Ferrari but effectively paid for by Maserati. Put slightly differently, Ferrari used Maserati (or rather their money) to develop the 4200 and once done adapted the design for their 430. Remember, this was at a time when Grandparents Fiat, were considering floating Ferrari on the Stock Exchange (possibly NYSE) and wanted their balance sheet as healthy as possible. The idea was then for Maserati to do for Alfa, what Ferrari had done for Maserati although little seems to have happened of late.
A quick word on endfloat and commiserations to those that have suffered this problem particularly since Maserati increased their prices for new cranks 3 or 4 fold:
Wicked is correct in that the thrust bearing cannot rotate with the crank as the lower half of each pair have tabs specifically to prevent this. However, when endfloat exceeds its tolerance of 0.006" to 0.008", the wear, therefore endfloat, can accelerate rapidly. An extreme case can result in so much wear that the endfloat can exceed the thickness of the remaining thrust bearing allowing the tab to pop out of its retaining slot and the bearing rotates with the crank chewing everything up in its path. By this time of course you would have little or no oil pressure and the engine would sound like a coffee grinder. Or is Conaero saying that top halves WITHOUT a tab have been wrongly fitted to the bottom??? Time for some photos of the old thrust bearings Conaero - All 4 please.
Why does a thrust bearing wear? Firstly, it is about the circumferance of an orange and is a steel backed, plain white metal bearing about 4mm thick. The steel side butts against the cylinder block sitting snugly in a machined recess and the white metal side (the bearing side) butts up against a flange on the crankshaft separated only by oil. It will therefore be seen that it is very similar in construction to a main or crankpin (big-end) bearing shell but oriented to control lateral movement. White metal is a very soft alloy - a bit like lead solder, containing a vey high proportion of tin, some antimony and perhaps even some lead. It is soft for a reason - Once "run-in" it will take on a perfect surface exactly matching the crank flange which is micro honed by the way. It does not need to be highly resistant to wear on its own - It does need to provide and contain a vital oil barrier.
The oil is fed at full pressure from the main gallery passing through 2 channels about 6mm or 7mm wide cast into the white metal face to allow oil to get between the white metal face and the crank flange. Correctly designed, bearings like this can take a huge amount of load (thrust) as long as there is an oil barrier between crank flange and the white metal face at all times. As long as the there is white metal on the bearing, the crank cannot wear beyond being polished - The bearing is soft, the crank is very hard so the bearing gradually wears. Once the white metal is worn away you are down to the steel backing, have very little oil pressure at this bearing thus loosing most of your oil barrier and steel to steel contact knackers the crank - Exactly the same as running an engine with knackered main or big ends bearings will quickly destroy the crank journals.
Perhaps I have led a sheltered life but I am astonished that a phosphor bronze has been used as a replacement thrust bearing. If there is damage to the block, can it not be repaired with plasma deposition and line boring? Expensive but not prohibitive and certainly less than a new block that you otherwise need. If there is damage to the crank, regretably you need a new crank. If both are intact, you could try oversize thrust bearings.
Perhaps now you can see why oil quality is so important.
hope this helps
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You can lead a horse to water but you cannot force it to drink
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