Line Honing is a HOT TOPIC for the Subaru Community.   The first thing we want to say is that it is NOT TYPICAL to REPAIR Subaru Main Bores. If the block is damaged, you most likely want to start over with a fresh "seasoned" block.   Line Honing for Subaru blocks is typically done when "High Torque ARP Case Bolts "are installed, which squishes the block more than designed, causing a slight distortion in the main bore.  Very little in fact, but this is an issue with the tight tolerances of the main bore. 

 

 A few solutions to consider.   In theory,  one could "Skim Cut" the case halves, torque down the block with ARPs, and line line the mains to STD size.  BUT... maybe consider that you do not want to skim cut the parting case halves if you can help it, due to the alignment to the transmission alignment pins.  Does it still get done at other shops all the time? Absolutely.  Is it potentially off by .003" per case halve? = .006"?  Hmmm... This can mis-align the transmission bell housing pins in theory.  To remedy skim cutting the case halves, King Bearings has made .002" and .005" Outer Diameter Oversize bearings.  This allows us to simply make the bore just a little bit larger vs. skimming case halves; attempting to shrink the main bores enough so there is material to hone. 

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So... What do we do?

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The first thing we do here at Subaru Machine is go the Oversize King Bearing route.  We start this procedure by torqueing the case halves with APRs; which in theory distorts the main journals.  Now under stress, the line honing can begin; truing the cylinder block main bore concentric and straight.  We can grow the cylinder bore to any oversize,  but most commonly to .002" or .005" for Kings unique O/S bearings on the O/D of the bearing shell.  Our line honing process is done to King Bearings main bore journals specifications.   We can have this process added to any of our projects when need be, and is always recommended when torqueing the case halves together with higher than OEM torque specs.