8Mud
NAXJA Forum User
- Location
- Central Germany
Near the distributor, there are letter stampings in the side of the block, that tell you if any of the crank surfaces have been cut smaller (under? spec.) typically 0.010". It must be fairly common, because 0.010" thicker (over? spec.) bearings are commonly in everybodies stock.
It's worth it to *me* to plasti gage the new bearing sleeves also, I am generally not a trusting sort (I'm going to measure and/or plasti gage everything before final assembly, just in case something is mismarked or whatever). Too small of an oil gap will kill your crank jiffy quick.
In my experience, in both the 4.0 and 4.2 (with which I have more experience). The connecting rod bearing sleeves wear in an egg shape, with the most wear being under the connecting rod shaft. The bearings seem to wear a lot more than the crank surface. The crank surface has a rather large tolerance when new, something like plus or minus 0.008", if I remember correctly. I'm a cursious sort, plasti gage is cheap, I've measured at four points on a single bearing many times. They sometimes wear in a cone shape, which can cause hot spots, with new bearings. I don't remember ever finding one with excessive side play.
I'm pretty careful about breaking in a new bearing set, I drive very conservatively for the first few hundred miles. Then change out the oil and drive moderatly for the next 600 miles or so. I avoid synthetic oils for break in. Sometimes the new bearings have to wear in some. The number of revolutions on the crank is what generates heat, I try to keep the RPM's down and pray a little, the bearings wear in, before they scortch.
The pump is producing volumn, the filter is producing restriction, the bearing surfaces should produce some restriction, the oil passges are small causing restriction, raising the pressure. If the filter is completely bypassed and has no restriction, your pressure may be low, but the volumn to the bearings and lifters should be good still (hopefully).
If you increase the RPM's the oil pressure typically only raises to a certain level, then stabilizes there no matter if the RPM's are raised still higher. The pressure relief valve is releasing (bypassing) and/or the drive gears in the pump are bypassing (loosing volumn) because the oil is getting hotter and thinner, possibly the oil filter is bypassing ( I was always under the assumption, that when the filter bypassed the excess oil went into the oil passages and not back to the pan). I've been looking for a good oiling schematic for the 4.0 forever and have never found a good one.
It's worth it to *me* to plasti gage the new bearing sleeves also, I am generally not a trusting sort (I'm going to measure and/or plasti gage everything before final assembly, just in case something is mismarked or whatever). Too small of an oil gap will kill your crank jiffy quick.
In my experience, in both the 4.0 and 4.2 (with which I have more experience). The connecting rod bearing sleeves wear in an egg shape, with the most wear being under the connecting rod shaft. The bearings seem to wear a lot more than the crank surface. The crank surface has a rather large tolerance when new, something like plus or minus 0.008", if I remember correctly. I'm a cursious sort, plasti gage is cheap, I've measured at four points on a single bearing many times. They sometimes wear in a cone shape, which can cause hot spots, with new bearings. I don't remember ever finding one with excessive side play.
I'm pretty careful about breaking in a new bearing set, I drive very conservatively for the first few hundred miles. Then change out the oil and drive moderatly for the next 600 miles or so. I avoid synthetic oils for break in. Sometimes the new bearings have to wear in some. The number of revolutions on the crank is what generates heat, I try to keep the RPM's down and pray a little, the bearings wear in, before they scortch.
The pump is producing volumn, the filter is producing restriction, the bearing surfaces should produce some restriction, the oil passges are small causing restriction, raising the pressure. If the filter is completely bypassed and has no restriction, your pressure may be low, but the volumn to the bearings and lifters should be good still (hopefully).
If you increase the RPM's the oil pressure typically only raises to a certain level, then stabilizes there no matter if the RPM's are raised still higher. The pressure relief valve is releasing (bypassing) and/or the drive gears in the pump are bypassing (loosing volumn) because the oil is getting hotter and thinner, possibly the oil filter is bypassing ( I was always under the assumption, that when the filter bypassed the excess oil went into the oil passages and not back to the pan). I've been looking for a good oiling schematic for the 4.0 forever and have never found a good one.
Last edited:
with Lucas and 20W-50, Impressive, most Impressive! 
