Actually, the plastiguage mashes down and the clearance is read by the
width after it is compressed. This is done by visually matching the width
with a guage that is part of the paper containing the plastiguage. Also,
you should note that plastiguaging should be done on dry bearings since an
oil film will take up clearance and give you an incorrect reading. There
is no need to remove the plastiguage from the bearings - it dissolves in oil.
The machinist's job is to ensure the crank is within specifications for an
undersize after grinding. In your case, factory specs minus 0.010". They
would not plastiguage bearings unless they assembled the engine. If the
crank measures correctly - suspect that the block needs line-bored.
Les Myer
At 04:09 PM 1/19/98 -0800, you wrote:
>go to your nearest automotive repair shop and find
>some plastigauge. it installs between the bearing
>shell and crank surface. when you torque the
>bearing to the recommended reading, it crushes.
>DO NOT rotate the crank with this installed. use
>some on each main and rod bearing surface. when
>you have completed this operation, remove the
>bearing caps and measure the plastigauge (keeping
>track of where each piece came from). you will
>need a micrometer for this operation. this will
>tell you the bearing clearance for each bearing
>surface. the macine shop should have done this,
>unless you didn't have the bearings at the time.
>you should have consistent bearing clearances
>across all surfaces, which are in the shop
>manual. for the 1275, main bearing clearance is
>0.0010 to 0.0027 inches (0.0254 to 0.067 mm), rod
>bearing clearance is 0.0010 to 0.0025 inches
>(0.0254 to 0.063 mm). hope this helps
>
>mike neff
>60 sprite an534446
>-----Original Message-----
>From: Guy Weller <GuyWeller@compuserve.com>
>To: spridgets list <spridgets@Autox.Team.Net>
>Date: Monday, January 19, 1998 11:53 AM
>Subject: Bearings - how tight should they be?
>
>
>OK, I've got my re-bored 1275 block and reground
>(-0.010) crank back from
>the engineer's shop.
>Assembled crank into block, without the pistons as
>yet, so I am only
>dealing with 3 main bearings.
>The crank is tight. Not so tight that I can't
>move it, but it certainly
>dosn't "spin" Should it ?
>I can just rotate it by hand -- two hands that
>is, but it takes a lot of
>force.
>It turns smoothly with a bar as a lever between
>the flywheel/ crank bolts.
>No high spots, but just stiff.
>Does that sound right to those who have done this
>job before, or should I
>scrape the bearing shells?
>
>Guy
>
>
>
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