Recently, I assembled a new 2001 era engine for the CSP Miata. 224 miles later at it's first auto-x, the #4 rod bearing spun at the end of the second run (many thanks to DILYSIdave for the tow!!).
The only items reused were the block, crank, and rods on the bottom end. The head, camshafts, and valves were the only used bits on the top. All re-used parts were machined, clearanced, and cleaned by a noteworthy engine shop. I performed the overall assembly myself and double checked rod and main clearances with plasti-gauge during the assembly and all checked out mid-tolerance.. The oil and filter were changed at 66 miles to remove any left-over machining debris. There was some metal on the magnetic drain plug, but not enough to raise any flags.
On to the oddities....throughout it's short lifespan, there was a light sound emanating near the #3/#4 area that varied with engine speed that sounded like lifter noise. I assumed that the lifter (shim) clearances weren't set properly at the shop. I later checked these during the postmortem to find them within tolerance. Furthermore, oil pressure during a 50-ish MPH cruise was hovering just below 90 PSI with the engine at operating temp.
Upon disassembly, I noticed heavy wear on the #4 and #5 main bearings as well as significant piston skirt to cylinder wall contact as well as some abnormal wear on the #2 rod bearings. My assumption is that there was a partial blockage somewhere in an oil passage leading to overall failure. Fortunately, all of the cam journals survived and are currently usable. I followed Flyin' Miata's break-in procedure and never noticed anything odd other than the points previously stated. Other than this, I'm at a complete loss.
Thoughts?
1-4, left to right:
2 rod bearing was significantly scarred:
4 and 5 mains weren't so good either:
).
