Re: Car Craft 360 AMC Build

[dsoutherland@xxxxxxxxxxxxxx]

On November 23, 2005 Frank Swygert wrote:

> Thanks Dwight! I imagine the comment I made about pressed in vs. floating piston pins come into play. The rod's not going anywhere if the pin is keeping it in place. Hmm.. that brings up something else though. The pin is pressed in the rod, and floats in the piston. With the big side clearance in the rod, the rod could conceivably move far enough that the pin scores the side of the block, assuming there is enough room under the piston for the rod to shift sideways that far. From what I recall there usually is. So running keepers as used with floating pins might be a good idea, or using floating pins. If the rod moves a little (piston will only let it move so far) there should be no problems. Maybe a slight drop in oil pressure over and engine with proper clearance, but that can be fixed with a stronger relief spring.

Frank, 
I have never seen a pressed rod/piston assembly where the pin would hit the cylinder wall when moved as far as it would go in either direction.  The piston and the rod require way too much material to allow such a thing to happen.  With a floating pin, the wrist pin boss in the piston will restrict the rod movement.  SBC rods are actually offset .060" less than AMC rods.  When you look at the assembly of the SBC rod in the engine with an AMC small journal crank (290-343, or 304-360), the rod is actually offset about.040" from the center with the rod against the cheek of the crank journal.  I suspect the operation of the engine keeps it in that position while the engine is running.

I am personally planning to use the new forged I-beam rods that AJ Jacobs is advertising in a new version of that 290 (or possibly a 360) combination I am looking at.


Dwight Southerland


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