On Tue, 30 Aug 1994, Richard Smith wrote:
> Rubbish!!
>
> The *real* pro uses 'plastigauge'. Most pros grind the crank to the
> required tolerance and fit the bearings it says in the book. Most pros
> couldn't calculate the difference between the main bearing housing diameter
> and the diameter of a trashcan lid!
Those "real pros" should stick to low rpm agricultural engines, then.
Pasti-Gage is okay for normal rebuilding, but in real precision engine
building the accepted method is to install the bearings in the rods and
mains (without the crank), torque down the caps, measure the inside
diameter of each bearing, then grind the crakshaft journals to provide
the required clearance.
> WRONG. If you need to measure the bearing clearance to this sort of
> tolerance, you need the above-mentioned 'Plasti-Gauge'. This is a plastic
> strip which you insert between the crankpin journal and the shell bearing,
> you then torque down the cap, light the cigar, remove the bearing cap, and
> measure the width of the Plasti-Gauge. You then compare the measured width
> with a table provided in the plasti-gauge pack, and - hey presto! the
> bearing clearance is revealed, to the nearest couple of tenths.
Plasti-Gage can't measure the clearance at a thrust bearing (which is where
this all began) since there is no bearing cap to tighten down. You need
to measure the fore and aft movement of the crankshaft with the thrust
bearing in place. On some engines you can do that with feeler gauges,
but in others you need to use a dial indicator (which is more accurate
anyway).
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Chip Old 1948 M.G. TC TC6710 NEMGTR #2271
feold@umd5.umd.edu 1962 Triumph TR4 CT3154LO (daily transportation)
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