Lesson 1/Learning Event 1
system as blue smoke. Burning the oil will lower the oil supply n the oil pan and cause a buildup of damaging
carbon inside the combustion chambers. Oil-regulating rings are placed in the bottom piston ring grooves to
scrape oil off the cylinder walls and return it to the crankcase. At least one--sometimes two--of these rings are
used on each piston.
FIGURE 23. PISTON PIN.
To reduce the weight of the pistons, the piston pins are made hollow. They are made of hard steel; therefore,
their ends must not be allowed to touch the cylinders as this will score their walls. Also, the pins must fit in
the pistons and connecting rods with the proper amount of operating clearance. Too little clearance will not
allow the connecting rod to swing freely from the piston; too much clearance will cause a knocking noise when
the piston changes its direction of travel.