350 vs 4.0 flywheel flange
On the left is the 350 crank, on the right is the Rover 4.0 crank. D&D fabrications sells a seal adapter for the 300 crankshaft, so I am having the 350 turned down to match. Below, you can see the snout of the 4.0 crankshaft is significantly longer than the 350 (and 300). This is to provide for a longer keyway to drive the crank driven oil pump. On the Buick 215, 300, 340, 350, Buick V6, and Rover V8s pre- 1994, the oil pump is driven off the distributor via the cam. The "N" is for "nodular" iron. The Rover crank is cast from spheroidal graphite, or "sg", iron, as are the main bearing caps. This is a post '94 crank with 2.4995" mains and 2.185" rod journals. The 300 crank is cast "Armasteel". The stroke difference is apparent between the 350, with 3.85", and the 4.0, with 2.8". So, what's the difference between "N"odular iron, and spheroidal graphite iron? Nothing, they are the same. Both are drop-cast iron with the graphite in ball form instead of flake. This results in a stronger crank that is still maleable (for cast iron) for shock resistance. The strength of these cranks is between that of a crap grey iron cast crank and a cast steel crank. The Armasteel crank is pearlitic maleable iron and is spun-cast in a centrifuge. These cranks are a even stronger than the nodular cranks due to the fact that a spun-cast crank is somewhat denser than a drop-cast crank. They are about the strongest stock cranks other than the steel cranks that were use in some high performance GM engines (the 1962 pontiac 421 "superduty" comes to mind).
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