Home away from home
From Melbourne Australia (and likely under the car)
I agree - there's too many possible causes to have a chance to diagnose it 100% for certain over the net. In this case, you're going to have to get in touch with a decent engine reconditioner, and let them inspect the lot.
So I'll ask a couple of questions, and any comments I'll make afterward will still only be guesses (educated guesses maybe, maybe not)
What were the bearing clearances when it was last re-built or put together? (all of them, rod, main, and even for the bearings that are still ok, just to get a clearer picture)
Any chance of some pictures of the bearings in question?
What oil pressure did it have at idle, and above 2500rpm or so (i.e. what was the max oilpressure), and what oil were you running (I'm asking about the viscosity, not the brand of oil in this case).
If the crank can be removed, can you look at each oil passage in the crank, and try shining light through each one. If there is debris in it, clean it out (collect it to get a look at what type of metal it is). Obviously there's likely to be some bearing material in there, but thhere is the off chance that there might be swarf left in there if the crank was re-ground the last time it was recoed.
It'd also be good to look at the other bearings - mark or separate them so you know which main cap or rod each one comes from. Don't just look at the bearing surfaces - flip each shell over and look at the back of them. If any of the other bearings have blue-ish marks (heat related discolouration, could also be a brownish colour - brown is high-ish temps, blue is higher temps than brown) - anyway if other bearings show such discolouration, it's likely that either the bearings were too 'tight' and didn't have enough clearance, or if there was oil starvation (though generally starvation will affect more than one bearing).
If the rod bearings, esp the upper halves have wear in the centre, it can be a sign of detonation that wasn't totally audible (and generally one cylinder will start detonating just before the rest, and which cylinder that is differs from engien to engine..)
You'd probably also want to look at all the upper main bearings, sometimes the oil hole in them doesn't perfectly line up with the oil passage in the engine main webbing/cradle where the bearing sits in. This can vary from engine to engine, but does happen from time to time. in some motors, there's different main bearings for different locations, or changes to the oil drillings from early to late model engines of the same type, so a mismatch can occur, and the solution is to check them carefully, and if hte new one is faulty, replace it, or if it's all that is available, it can carefully be drilled to open up the oil passage/supply
What else? You can sometimes fine cracks or pinholes in the oil pump pickup which can suck air and aerate the oil and compromise the oil supply - sometimes it can affect one bearing before the rest, but you'd tend to still find _some_ damage or signs of oil starvation on the others.
Posted on: 2011/10/28 11:33