known as a dial indicator or dial gauge, a dial test indicator (DTI)
is a device used in various automotive applications where small
distances need to be measured accurately, such as checking runout
on brake disks or end float on a crankshaft.
Runout can quickly ruin a disk if it exceeds the manufacturer's
specified tolerance (typically 0.15mm or less). So a dial test indicator
is used when fitting a new brake disk to check the axial runout
that occurs when the disk is rotated.
In the case of a crankshaft, a dial test indicator is used to make
sure that the clearance between the machined faces on the crankshaft
and the thrust faces of the thrust bearing are just right to permit
proper lubrication and allow for thermal expansion. If the clearance
is too small, there's the risk of seizure; if it's too great, lubrication
make fail because of loss of oil pressure. A lever is positioned
to move the crankshaft to and fro in order that the DTI can check
the end float.