} Subject: PLASTI-GAUGE
}
} How does PLASTI-GAUGE work? You put a piece on the old bearing and
} clamp (install) the bearing. This gives a measure of the wear I presume.
Not just wear, but actual clearence measurement. Proper clearence is an
important detail- Too little, and you get accelerated wear, or friction
which may lead to a seized or spun bearing. Too much, and you start
to loose oil pressure, and then the bearing gets hammered back and forth,
and you get rod knock or crankshaft wobble.
} Assuming the bearing (only) wears, and the crankshaft (or whatever)
} doesn't, what does PLASTI-GAUGE tell you that couldn't be determined
} by mike-ing the crankshaft? That is: measure the crankshaft and calculate
} the difference from "spec" measure, and buy bearings accordingly.
You still need to measure the crank, to get it's diameter, and determine
bearing size. But, both the bearings AND the crank wear. The crank may
also have been turned to a non-standard dimension. (Especially in
the case of a race engine, where everything is tweaked to the max,
possibly beyond standard specs) Variation can also be introduced by
condition of the engine block and bearing caps. Distortation can cause
ovality, skew, and other problems, which are corrected by accurate boring
of the assembled engine/bearing caps. (Align boring)
Plasti-gage is the only way to get a measurement of the actual
*assembled* dimensions, as opposed to the theoretical, calculated
results. It also shows topography. You can have
a bearing which is tighter on one side, which will show up as
tapered plastigage, instead of constant width. A bulge will indicate
a tight area, or a narrow spot will indicate a worn area.
} Is PLASTI-GAUGE useful to verify that new bearings & machine work have
} been done properly?
Very. You use it to check a worn engine, to determine how much wear, and
to check *all* bearing assemblys on new machine work and parts.
} DWhat should I expect the PLASTI-GAUGE to indicate for normal clearances
} at main bearings & rod bearings? The info is needed for a 1974 Spitfire
} with 1500 engine.
This information is found in the engine specifications of the service manual.
While I could cite "common" numbers, there is enough variation in specs
that you should always check the manufacturers specs. You will also find
a lot of other things which need to be measured when rebuilding an engine.
(Cylinder bores, valve stem clearence, head warp tolerance, etc.)
________________________________________________________
Roger Garnett (garnett@BATCOMPUTER.TN.CORNELL.EDU)
The South Lansing Centre For Wayward Sports Cars
"All donations of stray, orphaned, odd, neglected, etc.
sports cars and bits in need of a good home accepted."
"The drop off bin is right there- behind the barn..."
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