In-vehicle main/rod bearing change
 

Has anyone ever replaced rod or main bearings with the engine still in a vehicle? I know the rods/pistons cause issue and would make reassembly difficult.

Let me know because I may need to attempt this on a car based upon outcome of oil pressure test.

If not and it's required I can write-up some tips/tricks after it's all said-and-done. I'm not opposed to trying it but I don't want to do a complete rebuild on a stupid Dodge if I don't have to.

What qualifies something as a complete rebuild in your book? Taking the engine out? It seems to me that it would be more trouble to do the job in the car than out of the car. I have never done this job, but when I was in the bottom of my 4.3L I did think about how I would have accomplished this task if it was necessary.

First I would drop all the front end parts out, and the pan obviously. Then I would remove the transmission or at least unbolt it and slide it back a few inches on a jack so that the crankshaft can be dropped down. I would take off all the connecting rod caps except for one at each end of the crankshaft. Then I would remove the main caps and carefully slide it down using the friction of the first and last piston to support the weight of the crank and help keep it aligned so it doesnt bind in the journals. Pop the bearings out with a pick or screwdriver and maneuver the new ones in. Once the crank is re-installed, I would change the connecting rod bearings the same way. The big issue I think you might run into would be to do all this work then find the crank is scored, or the low pressure is due to something else. If the crank is worn, you will need to measure the wear and order different bearings. I have not replaced enough low end bearings to know what is typical for crank wear. In fact the only one I have ever done had no measurable wear, but that was a Toyota. If you have done several, then you might be able to make a good estimate of what replacement bearing size would be right. Does the engine have priority main or priority cam oiling? Maybe the low pressure is due to wear in the valve train. If it has a variable cam timing system that uses oil pressure for control or a hydrolic chain tensioner, those sort of systems could also be the source of internal oil leaks. Honestly, I think your best bet is to put a high volume oil pump in there and add some Lucas Mucus to the oil.

I put a high volume pump in the low end of my 4.3L and it brought the pressure from 20psi idling up to ~50psi warmed up on the dash gauge. It gets to 70 by 3000 rpm. I compared the housing size of the stock pump with the new pump to see quite clearly that it was about double the size of the stock pump and would therefore flow about twice as much oil. The Melling pump that I got has an internal pressure relief that ensures that the pressure does not exceed 70-80psi.

A complete rebuild in my book would be taking the engine out and down to every individual part to me checked. I've done engines before and complete is just that complete. I'm just covering my bases. It's on a '00 Dodge with a 2.5. The oil pump alone is $225 so I'm not going to throw parts at it. I have more time and patience than money at this point and I'd rather drop the bottom end and replace bearings than change a pump and end up changing bearings or something later when pressure is still low. However there is a hydraulic timing belt tensioner that I should also check while I'm at it. I don't think it uses engine oil pressure though but I'll take another peek just in case. Thanks for the reminder.

that info would've been good in the OP, not part way through.

since we're obviously taking about some FWD Dodge you own or know, i'm fairly certain there is alot of open space below the pan (ie; no subframe in the way).

in that case, you could drop the whole bottom end out after you seperate the trans a few inches. but how do you plan on holding the trans up after taking it off?

personally, if you're intent on just doing a "re & re" the bearings, i'd pull the engine out of the car since you can't support the trans easily, put it on an engine stand, flip it over & pull it all apart. slap in some new mains & throws, make sure it's all torqued down properly (after checking your clearences), and reassemble the drivetrain.

I was just in it for the what-if just in case. If the Blazer needed them I would give it a try.

oh, you were thinking about this applying to our trucks?

defiantely not worth the effort IMO. you have the diff in the way, and the 2nd gen non-hub design make it a RFPITA to remove.

i'd rather pull the engine for that.