Expand the small hole gauge in the bore, lock its position ...

Then measure the gauge with a micrometer

lines up exactly with any of the divisions on the main scale, noting that the divisions usually represents 0.02 of a millimetre. Add this fine measurement to the base measurement to obtain the total reading.

Tools and Workshop Tips ref.h

Vernier component parts (linear gauge)

5 Sliding scale

6 Main scale

Base measurement Fine measurement Total figure

• Some vernier calipers are equipped with a dial gauge for fine measurement. Before use, check that the jaws are clean, then close them fully and check that the dial gauge reads zero. If necessary adjust the gauge ring accordingly. Slacken the vernier clamp screw (1) and set its jaws over (2), or inside (3), the item to be measured (see illustration 3.13).Slide the jaws into contact, using the thumbwheel (4) for fine movement. Read off the main scale (5) where the edge of the sliding scale (6) intersects it, taking the whole number to the left of the zero; this provides the base measurement. Read off the needle position on the dial gauge (7) scale to provide the fine measurement; each division represents 0.05 of a millimetre. Add this fine measurement to the base measurement to obtain the total reading. In the example shown the item measures 55.95 mm (see illustration 3.14):

Vernier component parts (dial gauge)

1 Clamp screw 5 Main scale

2 External jaws 6 Sliding scale

3 Internal jaws 7 Dial gauge

4 Thumbwheel

Plastigauge

• Plastigauge is a plastic material which can be compressed between two surfaces to measure the oil clearance between them. The width of thecompressed Plastigauge is measured against a calibrated scale to determine the clearance.

• Common uses of Plastigauge are for measuring the clearance between crankshaft journal and main bearing inserts, between crankshaft journal and big-end bearing inserts, and between camshaft and bearing surfaces. The following example describes big-end oil clearance measurement.

• Handle the Plastigauge material carefully to prevent distortion. Using a sharp knife, cut a length which corresponds with the width of the bearing being measured and place it carefully across the journal so that it is parallel with the shaft (see illustration 3.15).Carefully install both bearing shells and the connecting rod. Without rotating the rod on the journal tighten its bolts or nuts (as applicable) to the specified torque. The connecting rod and bearings are then disassembled and the crushed Plastigauge examined.

Date: 2016-01-14; view: 781