Crank and Bearings - assessing serviceability?

[Kevin Trent <trentkc@domain.elided>]

I never saw a response to David Johnson's questions from V8 #617:

<SNIP>

>I pulled a main bearing cap and a con rod cap for further inspection.  Both
>bearing shells appeared fairly little worn, suprisingly so for an 80K mile
>engine (don't believe the bottom end has been rebuilt, but I'm not certain).
>No signs of copper coming through, although I did not check the thickness.
>But both shells, especially the main beraing shell, had a lot of small
>flakes embedded in them.  Flat bits of metal up to maybe 3-4 mm across.  I
>was able to gently pry off a couple flakes and they appear to be steel,
>since they are attracted to a magnet (the soft bearing material is
>presumably not magnetic).  The larger particles in the sump oil are also
>attracted to a magnet.
>
>I next inspected the crank journal surfaces.  Some very faint
>circumferential lines were visible on the main journal, less on the big end
>journal although a couple of more visible lines.  None of these lines seemed
>deep enough to catch a fingernail dragged across them.  It's hard to reach
>the liners with only the lower pan removed, but the surfaces looked pristine
>and I could detect no scoring there.

I have the same question.  In a 1750 I've disassembled for a budget 
rebuild, the bearings look generally good, though a few do have some 
pinhead size bits of metal imbedded in the bearing surface, and some also 
have very fine lines as described above.  The crank has a few journals with 
faint circumferential lines too, but pass the fingernail test, e.g., too 
faint to catch a fingernail.  The engine had good oil pressure prior to 
disassembly.

Braden's AR Bible states:  "Under normal wear, a crankshaft's bearing 
journals will become lightly scored.  This normal scoring can be cleaned up 
by polishing the journal with crocus cloth...The rule is that, if the 
scoring is deep enough to catch your fingernail as you draw its edge across 
the bearing journal, the journal must be reground to undersize than 
polished."

What is 'crocus cloth'?  Same as wet/dry sandpaper used for color 
sanding?  What grit?

I want to reuse the bearings - this will be a substitute engine to 
temporarily replace a 2L during its rebuild.  Won't get a lot of miles, not 
expected to last forever.  I've been meticulous about disassembly and can 
put all bearing shells back exactly as they were originally.  Should I 
polish out the crank lines or just reassemble?  I'll use old pistons and 
liners too - hone the liners, and use some NOS borgo rings. New Gaskets and 
seals.  Maybe a new bottom chain.   Comments??

The head is another story..

Thanks,  //kct, Powell, TN (saving my $ for the 2L rebuild..)

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