<VV> #1 main bng

[BobHelt at aol.com]

Hi Guys
Here is another look at the #1 main bearing change after a  little research 
on the matter.
 
Regards,
Bob Helt
 
 
 
It’s  interesting to note that during the 1962 production run on 16 April 
1962, there  must have been a batch of incorrectly sized #1, flanged main 
bearings received  at the Tonawanda  engine assembly plant (Stated in a Tech 
Bulletin issued by Chevrolet). This  mis-sizing apparently was in the flange 
portion of the bearing, which controlled  the amount of endplay of the 
crankshaft. In order to use these bearings without  interruption to production, 
engine assembly continued by using only a  half-flanged #1 bearing. This was 
accomplished by using just one of the pair of  flanged inserts along with an 
insert identical to the #2 and #3 bearings. Soon,  after-market bearing 
manufacturers were erroneously producing bearing sets with  just the 
half-flanged #1 main bearing. 
Now  here is where the story gets interesting. The Tech Bulletin definitely 
referred  to a “mis match” of the two flange portions of the #1 bearing. 
That would  indicate a bearing supplier problem; and a temporary problem 
until the supplier  could resume supplying the correct parts. Although we may 
never know just what  happened to cause to shift to the half-flanged bearing, 
we do know that for 1963  production new half-flanged bearing drawings were 
released. Why would new  drawings be released unless this was intended to be 
a permanent change; or was  there was another reason for the switch to 
half-flanged bearings? Maybe this was  done as a cost reduction instead, or even 
as a solution to some other technical  problem. Also for 1963 production, 
the turbocharged engines received the new  full-flanged aluminum bearings. So 
for all of the 1963 production, except for  the 150 hp turbo engines, 
half-flanged bearings were used in production. One  would rightly assume that if 
it were a supplier problem, they would have fixed  the problem in much less 
time than a year and a quarter. So it would look like  the real reason for 
the half-flanged bearings was something other than just a  simple 
mis-matching condition. 
For  the 1964 production, the factory converted entirely to the new Moraine 
M400  Aluminum double-flanged bearings and continued to use them until the 
end of  production in 1969. 
Despite  the fact that Chevrolet resumed production for 1964 using the 
full-flanged  bearing, the aftermarket bearing manufacturers continued to 
produce these  half-flanged bearings for all applications and all years right up 
to the present  day. Of course, the half-flanged bearing will work 
satisfactorily, but most  rebuilders prefer to use full-flanged bearings as were used 
by the factory,  except for this short period during  1962-1963.
 
 
 
 
 
 
In a message dated 10/8/2013 6:26:25 A.M. US Mountain Standard Time,  
62vair at gmail.com writes:

Lon, for  #1, maybe they did both, steal a good flanged half and a extra
un-flanged  half to get two sets. Or,