How far is ok for a crank to be ground?

Duane said:

My crank is at .030 now and needs to be machined again. I have another thats already at .020 but it's pretty rough. Is .040 ok for less than 500hp? Or keep looking for another crank?

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A -0.040" undersize crankshaft for a 500 hp engine is fine. And it might even be debated to be technically better suited than a standard/standard crankshaft, but that's really splitting hairs and in reality one is not necessarily better than the other except for the amount of the crankshaft's remaining service life (future regrinds).

Don't worry that it's -0.040" undersize; regardless of journal size any crankshaft has to come out again if it gets damaged so it isn't important whether it's standard or -0.040". If you can get bearings for it, a freshly turned crankshaft may be considered a "good-as-new" crank in a case such as yours, and will last as long as a standard/standard crankshaft in your bulid.

Paul

Duane said:

Is .040 ok for less than 500hp? Or keep looking for another crank?

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Many, many, many Ford 460 cast crankshafts have been turned to -0.300" undersize (three hundred thousandths, or ten times a -0.030" under crank) and have been known to hold as much as double the horsepower you are referencing.

Just for reference, King Engine Bearings makes all the way to .060 undersize.

Hope that helps,

Dave

Thanks guys, I was just worried about the bearings themselves in performance usage. My buddy would turn the rod journals down and use 440 Six Pack rods in them back in the 70's

WHATEVER you can get in bearing sizes will be fine for a lot more power than you are using.