This work is best completed ...after... Pulling this LL8 Motor and mounting it upon an Engine Stand with it naturally being inverted and Pin-Locked in place upside down. The main reason for this is because the Crankshaft in these Atlas Vortec 4200 Motors is NOT held within its *Crankshaft Orbit* inside of the Mains Cavities of the Lower Engine Block with Individually Bolted Down Seven Mains Journal Caps.
The amount of aggravation this brings to this task is already self-evident in your original post entry... and THIS issue is only the beginning with trying to access and remove those Different Sized Crankcase-Oil-Pan Perimeter Bolts-Nuts.
Unlike performing the typical "Upside Down Mains Bearings R&R" that Mechanics are familiar with doing in the conventional manner (one journal at a time)... it is NOT possible to do this with the Atlas Vortec 4200 Engine installed in the SUV.
This is because ALL of the Mains Bearing Caps are held in place with One Single Steel Cradle such that Cradle Bolts must ALL be removed FIRST before you can even access ANY of the Individual Mains Caps and rock them loose underneath to perform the Mains Bearings R&R.
Please remember that the Crankshaft is VERY LONG and VERY HEAVY in this Motor.You also have to add in the weights of the Harmonic Balancer at the nose of the Crankshaft ...and the Flex-Plate and possibly a loose Torque Converter bolted at Three Points to the Flex-Plate on at the Rear of the Crankshaft.
It follows on from here that this leaves the Heavy Crankshaft and those attachments free to add their combined weight and risk DROPPING DOWN via Gravity while dragging the additional weight of the Connecting Rods & Pistons right along with all of it.
Thus, this can create Very Heavy Pressure against the lower areas of the Front and Rear Aluminum Plates (Timing Cover -Gerotor Oil Pump and Rear Bolt On Plate) - Oil Seals and risk CRUSH DAMAGING them, since both Seals contain tightly wound and very delicate Coil Spring Expanders nested inside to supports the *Plumpness* of the PTFE (Teflon) Oil Tight Dust Seals and to maintain steady contact with these Rotating End Journals.
Besides having to contend with the aforementioned Three Front Crankcase-Oil-pan Bolts... there are also TWO MORE BOLTS hidden and well nested in between the Parting Line at the BACK of the Engine Block-Rear Oil-Pan and the FRONT Flange of the Bell Housing that will require removing the Two Rubber Plugs from underneath FIRST and then snaking a Deep Metric Socket up in there to unwind those Two Hidden Oil-Pan Fasteners.
If you don't do that action as well, you'll wind up accidentally breaking off the rear upper lip of the Crankcase - Oil-Pan....And... Well... Just look up "Kevin Nadeau's Five Part Series" covering working on this Engine while it is STILL Dwelling in the Engine Bay of his 4WD Envoy over on YouTube to get a MUCH better idea of all the problems that HE had to overcome.
