Cummins Engine ISX 475 , 920000miles, oil pressure 38psi at warm prior to changing the main and rod

Depends where you took it to i know a lot of shops around the chicagoland area are kind of shady with the type of work they do. When you have a repair done make sure you tell them to save the old parts that way they can show you i do that with my customers all the time that way they know what exactly was bad and how it went bad.

 

Here is one rule in hydraulics - liquid is going the way with less resistance to flow. If you didn't overhaul cams bearing oil will mostly go this way and new crank and rods will starving on oil. this will cause them to spun and pressure drop even more. Hopefully shaft is still OK

 

I'm going to state up front that I have never rebuilt a diesel engine, but I have rebuilt a butt load of gas engines. I would think it would be standard to measure the crankshaft journals. If they are out of spec, the crank would be turned or replaced. Putting new bearings on an out of spec crank could reduce the oil pressure. Were your charged for the crank being turned? Is the part numbers for the bearings they installed on the invoice? If it is a practice to turn diesel crankshafts, there are bearings that compensate for the reduced size of the journals. .010 under .020 under etc. If the wrong undersize was used, it will affect oil pressure. If the drop in pressure is due to improper bearing fitment, the new bearings will have a short life. How short is anyone's guess. I would have an oil sample taken, preferably from that oil change you did, if it was collected in reasonably clean containers, to see if there is excess bearing material in it. You might have to wait for the next change. I've never seen the oil pump on that engine, but I'm sure it has an o-ring or gasket that seals it to it's mating surface. If it's leaking there, it will reduce oil pressure. I'd have that pump changed now. A bearing journal can be removed to visually inspect a bearing. I think I would change shops if I were you, as they one you have used isn't very thorough, nor concerned about your satisfaction, according to your remarks. If I'm wrong about the servicing of diesel crankshafts, maybe someone will say so, or you can ask a mechanic. Hope this isn't a gopher hole. Best of luck.

 

I have done big diesel engine overhauls on a stand before and its super easy to remove and measure the crank. During a bearing roll with the engine in the truck you don't have that luxury unfortunately. Typically you remove 1 cap at a time, roll new upper bearings and then re-install the cap with the 2nd half of the bearing. Super PITA to get an accurate main bearing measurement as well with crank still in the block.

 

I've never watched an in frame done. But from the trucks I've been under there appeared to be enough room to remove a crank. I've seen cranks removed from cars that I never thought would be possible. Doesn't sound to me like a repair that would be worthwhile, not knowing the foundation you are building on. Thanks for the info.

 

Its been a while since I've been into an engine but I seem to remember that you'd need to remove the transmission, flywheel, flywheel housing and probably a bunch of parts, if not the entire front cover in order to get the crank out. Engine mounts are on the flywheel housing too so you'd need to support the engine as well. Some import diesels like the big inline 6 Isuzus use a girdle instead of individual caps, which means the engine's coming out for new bearings.