Rod bearing throws on #2 and #4 are fed by seperate drillings.
Strange Rod Bearings Failure
This engine died of #4 rod bearing failure and separation (and the usual massive damage that goes with it) without turning two full miles on the track. And the #2 rod bearing was about to go, worn down to a thin sliver. In that this is the first time I have ever seen this specific type of failure in one of my own engines, I hope someone will come up with a clue.
Specs
AS41 case, line-bored twenty over
Windage tray
Oil "suction" pickup and dished oil plate. No strainer
Case oil pickup tube seated and tight
All new Mahle bearings
EMPI 74mm counter weighted crank (new out of box)
Stock VW rods (Bugpack) used but balanced and rebuilt
85.5mm Mahle piston and cylinder set
A.J. Sims heads, 46.4cc combustion chambers, 9.4:1 compression
Auto Linea G03, Dual springs
40mm Intake Valve, 35mm Exhaust Valve
A.J. Sims cam & hardened lifters
Cam LBC 3-108*LC
Lift (1:1) 461, Duration 290
32mm full flow Oil Pump (direct pump to HP1 filter)
8-Pass remote oil cooler fed by adapter from case top, electric fan-cooled
Grooved oil pressure relief piston, stock spring
Ungrooved oil pressure control piston, stock spring
Oil: 15w40 Castrol Tection Diesel with ZDDP
Carbs: EMPI HPMX copies of Weber 44IDF's
Shop run-testing was good, oil pressure all in spec. Throttle response good. At track test day, we get rod bearing knock right away. While in paddock revving engine (3000rpm+) to listen for knock, #4 rod blows through top of case.
Tear down reveals cam broken into four pieces, #4 rod seperated at bolt side, but bolt is found intact, nut stripped right off threads and crushed, and #2 rod bearings almost worn away.
All mains were good, and rod bearings on #1 and #3 excellent. The only other bearing damage was from dust-fine case fragmentation bits that had only a couple of seconds to try and circulate to the bearings.
Blowing air through case oil passages revealed no stoppages. and removing the set screws from the crank drillings and poking long steel probes inside finds that the interior crank drillings are in fact there.
How can two rods, fed by different crank passages, die this fast?
Any suggestions are welcome.
FJC