When I was in high school auto shop we saw a film of a guy doing a main and rod bearing change from the bottom. We all agreed (including the teacher) that that was the dumbest way to do that job. Why not just pull it? I tend to agree (still).

 

Ive seen them done with the engine in the vehicle in some shops Ive worked in... Mind you it was on something that the oil pan would fall out of when undone, and 6 and a half feet up in the air.

 

some jeeps you can get it done from underneath if they are lifted high enough. a blaze though? i wouldn't try it to much stuff in the way. by the time you get it to the point of where you can get the crank out it would only 5 more mins to pull it the rest of the way out and do it right. i would check the sending unit first. dads friend has a jeep and the oil pressure was really low, and by really low i mean it wouldn't get over 20psi cold or warm when you were driving it. at idle it wouldn't even move the needle. i hooked up a mechanical guage and it was actually getting about 60psi all the time. changed the sender and it was fixed.

 

i was able to get the oil pan off by loosening some of the body mounts, it was loosing oil pressure because the pickup screen had fell off. i pulled one main and rod bearing, they both looked good, so i didnt replace the bearings. if i were to replace the bearings i would definatly pull the motor because it is very tight to get a torque wrench in there.