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Discussion Starter · #1 ·
Hi all,
Have a 4.7 from a 2008 dakota that i have been rebuilding. Not my first rebuild but im definitely no expert. Engine had about 200k and a decent knock. Removed the engine and tore the whole thing down. Found 2 wasted rod bearings on cylinders 3 and 5, but all other bearings were good. Cleaned the block and all parts and reassembled with new bearings, piston rings, oil pump, gaskets, timing kit, etc. Also got a reman crankshaft (.010 under) with matching bearings. Checked rod bearing clearances and all was good. Got lazy and didnt check mains though (learned my lesson). Engine actually started right up. Broke it in for a bit but after an hour or two, got a low oil pressure light (ouch). Only came on when engine was hot and only at idle (went away above 1000 rpms). Got a mechanical gauge to confirm and yep it dropped to 0 at idle when hot. Played around with different oils but bit the bullet and removed the engine and disassembled again. Instead of plastigage, i decided to invest in a set of outside micrometers and a dial bore gauge. Got the engine apart and actually got yet another crank with bearings from engine tech (also .010 under).

Went to do things right this time. Put the main bearings in, and torqued down the bedplate according to spec. Measured the crank journals with the mic. All were exactly the same and at 2.4899 in. Add .010 and got 2.4999. Specs call for 2.4995-2.5005 so crank is all good for sure. I then zero out the dial bore gauge on the mic and check the clearances on the main bearings inside the bedplate/block. I seem to be getting crazy numbers. At 12 oclock/6 oclock (straight up and down), i get anywhere from .003 to .006. At 10 oclock/4 oclock, i get as small as .0015 on one or two of the bearings, but most are from .003 to .005. One or two of the bearings are off as much as .002-.004 when moving from 12 oclock to 10 oclock. These clearances are very loose and i imagine could be causing my low oil pressure. Ive never had an issue like this before. I made sure the bedplate was clean and torqued right, i must have done it like 5 or 6 times. I’ve checked and rechecked my measurements. Specs call from .0008 to .0021 in for main bearings, which makes my clearances almost 3x bigger in some cases. I tried a different set of .010 over bearings and got the same. Even though i knew the crank was good, I tried the other crank i had…same thing. These were brand new Engine Tech bearings. I also tried Plastigage…again showing clearances over .003. Is it possible that the casing of either the bedplate or the block is worn too much or has too big a diameter? I looked in the specs for how big the diameter of the crankshaft casing is supposed to be but they don’t seem to give that spec. Maybe someone tried to line bore this thing at one point? Im running out of options and really dont want to put the motor together without getting good main bearing clearance numbers. Also, i know some bearings tend to be a bit eccentric when torqued, but is it normal to get a reading that is .002-.003 different from the 12 oclock position to the 10 oclock position?

Any suggestions that anyone can provide is much appreciated. I want to assume that im just doing something wrong, but the measurements look good on the rod bearing clearances using the same method so i dunno, i must be doing something right
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