<VV> fwd: Polishing Crankshafts

PatioMatt@aol.com PatioMatt@aol.com
Wed, 26 Jan 2005 14:24:10 EST


In a message dated 1/26/2005 10:55:16 AM Pacific Standard Time, 
dunlapsville@yahoo.com writes:


RE: ........................... On Tufftrided, Nitrided, and nodular iron 
cranks there 
are tiny surface scales and flaps that need to be smoothed down like 
petting a porkypine in the "right" direction........................
  
I was under the impression that all Corvair cranks that were "Tuffrided" 
(nitrided) were steel (forgot the actual SAE class: 4300 I think.).  

Polishing crankshaft journals:
  
1) Get a 30" length of  leather shoe lace.  $3.50 at Wal-Mart's outdoor dept. 
or any shoe repair shop.  
2) Get the appropriate sized OD mic that reads in .0001" (tenths),  eBay 
$15.00 or so.  Starrett, Brown &Sharpe, Mitutoyo, etc.  Get a good one.  It'll 
last you until the second coming or you loose it in the divorce decree whichever 
comes first.   
3) Get one (1) sheet of crocus cloth.  $1.50 at your local FLAPS.  You may 
need to call around some.  3M makes it and ALL auto parts stores used to carry 
it.  In the olden days it was 50 cents per sheet.  Keep looking; you'll find 
some.  One sheet will do about 5 cranks.  FYI crocus cloth is jewelers rouge 
(iron oxide) on a cloth backing (like emery cloth) and is used to polish jewelry. 
 It has the smallest (finest) grit commonly available for polishing anything. 
       
4) Get a wooden paint stirer at your local Home Depot/Loew's store.  Get 
three; they're free.
5) Get a flat piece of 3/8" steel or a flat file that will fit between the 
throws of the crank.  New file $10.00. Any old worn out file flat file will do 
nicely.  Cost = free.
6) Mike each crank journal (both sides and every 90* around it. You want to 
know up front any taper and out-of-round condition of each journal before you 
begin. Write the results down for each journal !!!!!!  Don't ASSUME anything.  
You 'll never remember what they were after you started.
  
Depending on the length of time that the crankshaft was left in the salt bath 
has determined how deep the nitriding is.  Usually it is only .0002" to 
.0003" deep (about 1/10 the width of a human hair).  You should only need to take 
less than .0001" off of each journal to make them shiny.  Thats 50 millionths 
per side here!  Even if you take .0002" off of them its still only .0001" per 
side so you're still OK.   

7) If you have a lathe use it to hold the crank as you spin it at high speed 
for the mains. Nice but not necessary.  Be careful here!  Use the crocus cloth 
backed by your free paint stirer and then the file.   The file just lets you 
push harder and control the cutting action of the CC.  The corcus cloth will 
do the polishing of the journals W/some light oil.  The idea is to get the 
journal shiny and not tapered. Stop, wipe the journal clean and measure it often.  
If you find a taper (or more likely you start to make one) push harder on the 
big side to take it down to size.
  
No Lathe, No problem.  
  
8) For the connecting rod journals tear off a strip of crocus cloth and using 
the leather thong wrap it around the journal twice so that it completely 
holds the CC on and both ends of the thong comes back to you.  It helps here if 
you use two pieces of old broom handle to make handles like the old pull 
starters on lawn mowers.  Your call here.
9) Add some light oil and polish away by pulling the thong  back and forth 
causing the CC to spin completely around the journal(s).  Check as you go!  
Write the diameter(s) down!
10) Do the same for the mains if you don't have access to a lathe.   Be 
thinking about getting one though.  They are almost as handy as money.  Actually 
handier on late Sunday afternoons and just before all final late night thrashes! 
 Been there, done that, got many T-shirts!
  
When all of the journals are shiny record each diameter so *IF* you have to 
selectively fit bearings you know EXACTLY what you need and where you needed 
them. 
  
Don't forget to clean the crankshaft completely and grease the nice shiny 
journals IF you are NOT going to rebuild the engine immeadiately.     
  
Regards, Ken   dunlapsville@yahoo.com