Next up in the disassembly phase was to remove the oil pump, which mounts to the front of the crankshaft on the Northstar. It's very different looking than the far more common pump on a Small Block Chevrolet engine:
Since it was on the list of things to be replaced regardless of its condition, I decided to take it apart and examine it. The main things I was looking for were:
A. deep scratches or uneven wear on the gear teeth;
B. scoring on the sides of the rotors and their mating surfaces on the pump housings;
C. scoring on the outside diameter of the outer rotor; and
D. checking to make sure the pressure regulating piston was free to move fully into its bore.
After the oil pump was off, I was able to inspect the primary timing chain, crank, and secondary sprockets, which all looked fine. The primary chain however had eaten through nearly 75% of the chain tensioner's cushion block, so it was near the end of its life. It’s the kind of thing that might have lasted another 20K kms, or only 5K.
The next step on the tear-down was to remove the connecting rods and pistons. To do that, I spun the engine upside down on the stand, removed the oil pan...
...and rotated the crank until the bolts holding the connecting rod bearing caps were accessible.
Once the cap bolts and bearing caps were removed, each connecting rod and piston assembly was simply pushed out through the top of the upside down engine one by one.
Here’s where being skeptical of the condition of the engine paid off big time… after I had removed several pistons, something went clinkity-clink on the floor when pistons 2, 4 and 6 cleared the block. Unfortunately it wasn’t just a couple of broken rings...
... this was far more serious... the pistons themselves were broken despite having given good compression pressures when tested earlier. The fact that the pieces had stayed in place and hadn’t scored the cylinder walls was amazing.
After having consulted with my machine shop, the consensus was that this was probably caused by detonation... poor ignition timing. Luckily there was no secondary damage… well, except to my wallet. Apparently they don't simply give away new Caddy pistons.
That summed up the bad news about this particular engine, there were no more surprises waiting for me (whew!). In summary, the exhaust cams, cam followers, valves, and timing chain tensioner were worn out, as well, three pistons had broken ring lands.