<VV> Do I have crank problems ?

Mark Durham 62vair at gmail.com
Sun Oct 24 23:20:06 EDT 2010


Charlie said:  Does this mean I DO have crank problems ?

With wear through the babbit and into the copper, that indicated very
high mileage to me (or severe wear) and have you pulled the lifters
(one at a time, CRITICAL, don't mix them up) to check for spalling on
the cam lobes and lifter bases?  If you have any, its time to pull the
engine and split the case. If not, then certainly proceed to fix it
because main bearings rarely cause a problem.

Charlie, check the rod journals to see if they are smooth or out of
round with a micrometer. You can do a bit of micro polishing to remove
tiny imperfections with some very fine crocus cloth. When smooth and
round, then measure, and see how they match up to new dimensions of
1.799 to 1.800 inches. If you have journals at 1.798, you could use a
set of .001 or .002 bearings, 1.797 needs  .002.  or .003 and so
forth. Any more than that, its time to have the crank reground.

Always check with plastiguage, but you have to do the preliminary
measuring like above to get the right parts then verify journal to
bearing clearance in the .0007 to .0027 range with plastiguage.
Obviously, a tighter clearance will last longer, so I tend to try to
get my beating clearances in the .001 to .0015 range..

Yes, if you are changing some bearings, change them all!, You don't
have to remove the cylinders to do this, just rotate the crank around
and push the pistons up into the bore enough to move the rod up and
work on it. I did this on my engine. Tedious, but doable. Buying
bearings as singles costs more than each in a set, so you really are
not saving anyting and there is peace of mind as you are racing down
the freeway at 70, OK, 68 so its easier for the "lookers" to pass you
and stare at the "old car".

Oh, a web site where a guy is building a Corvair engine for a
airplane, but excellent pics on cylinder, crank, rod work you will
like.
 http://www.hainesengineering.com/rhaines/corvair.htm#rods

regards  Mark Durham


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