Home » » Sketch and describe a bridge gauge. How is it used? What other instrument could be used in it place of the bridge gauge?

Sketch and describe a bridge gauge. How is it used? What other instrument could be used in it place of the bridge gauge?

Sketch and describe a bridge gauge. How is it used? What other instrument could be used
in it place of the bridge gauge?

The bridge gauge is also called the Lloyds gauge is reliable method in checking the wear down of
main bearing. The bridge gauge is of steel construction with machined faces which will rest on
the machined faces of the bedplate.

The bridge gauge is especially designed for the engine in question and cannot be interchanged
between engines. To check for the wear down using these method top halves of the bearing can
be removed and the halves of each journal relative to the machine uppermost face of the
bedplate is measured. This is done by placing the bridge gauge across the crank journal in the
place of the top half of the bearing. If the bearing has worn of the crank sagged, there will be a
clearance between the bridge gauge and the top journal. This clearance is then measured using
feeler gauges. The value is compared with the value stamped on the bridge gauge for that
journal, which are the manufacturer’s specifications.

Any number readings should be recorded and attached to the engine, as a permanent record. If
the original gauge reading is subtracted from the new reading the result is the combined wear
down of the bearing and journal. However as the wear down on the journal usually very small,
the bridge gauge reading are usually accepted as the bearing wear down.

In some cases where to shaft has not sagged, but the bearing are suspected of wearing a
hydraulic jack is used to jack the crackdown on to the bearing. The bridge gauge is then fitted in
place and he clearance recorded, thus giving the bearing wear down.

There are several sources of error involved with using a bridge gauge. The feet of the bridge
gauge may have been placed on dirt, or there may be small burrs on or under the feet. These
faults will result in high readings. To reduce the chances of error, the surface below the bridge
gauge feet and the feet themselves as well as the journal should be thoroughly cleaned. In some
engines a specific location is scraped up for taking the readings so that the reading is the same
throughout the engine when it is new. If the bridge gauge is moved from this especially scraped
area, errors in readings will result. Instead of using the bridge gauge to measure wear down a
dial gauge, deflection gauge or a clock gauge can be used. A clock gauge is used in the same
manner as a bridge gauge, expect the clock gauge records the readings instead of having to use
feeler gauges.

There are several factors which contribute to bearing wear down such as:
1. Unequal power distribution in the cylinders
2. impurities in the oil such as debris
3. interruption in the flow of lube oil, which would cause overheating and possible melting of
the bearing metal
4. If different bearing are lined with different anti-friction material, then different rates of wear
would occur


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