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First engine build, is this crank ok for my use?

Posted by 406_Talon, Jan 21, 2021

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  1. 406_Talon

    406_Talon Supporting Member

    Joined Jun 30, 2014
    Kalispell, Montana
    So I am building my first motor, nothing special just Manley h beams and pistons, stock crank 450 horse goal kinda deal. I had acquired a used 7 bolt crank to use, and upon measuring it it’s a bit out of spec - #2-#4 rod journals are 1.7710 - 1.7712” which is it great, but the #1 rod journal is a measly 1.7708” and that seems, well... bad. But, my rods specify an oil clearance of .002 - .003”, and based on a nominal rod journal bearing spec, since I don’t have my block ready to compare it to, I would be at @ .00226”. So, should I make a paperweight out of this crank or could I cut the other journals down to 1.7708” and send it, maybe with oversized bearings? Am I out of the nitride? There is one little nick on the #3 journal, pic attached, that I can see but can barely feel, so I had meant to have it polished anyway. Any advice would be appreciated.

    Attached Files:

    Street Build 1K  3

    1995 Mitsubishi Eclipse GSX
    awd · manual · 2G DSM
  2. DSMPT

    DSMPT DSM Wiseman

    Joined Jun 12, 2014
    Japan / Mexico, Arizona
    If we assume the crankshaft is perfectly straight and all journals roundness/taper numbers are good and if the numbers you measured are accurate, I think that crankshaft is fine. The max difference is .0004, this wouldn't be a problem in general. You even would see +/- .0001" difference on a new crankshaft. So I don't think you need to worry much about that difference.
    To be honest, you can't really know the actual clearance until you physically measure it with bearings by a micrometer and a bore gauge. And if you want to make the difference less and more accurate, you can adjust it by asking a machine shop to polish the journals or/and prepare a couple of bearing set (same size set/.001"extra or less clearance set/different manufacturer) and then take bearings from different set to make you own set (don't mix different manufacturer/material and over-under size in the same pair). If speaking strictly, even with the same size/same part number sometimes slightly different between sets and manufacturers. Also your .0001" and machine shop's .0001" may be different due to the tool's accuracy and how to use the tools, too.

    Drag Race Build 3K  7

    1990 Mitsubishi Eclipse GSX
    awd · manual · 1G DSM

    Street Build 2K  4

    1998 Mitsubishi Eclipse GSX
    awd · automatic · 2G DSM
    TK's9d2TSi likes this.

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