IO-240 Series Engine Installation & Operation Manual
2-9
31 October 2011
Engine Description
2-2.4.1. Pistons
Pistons (Figure 2-10) are aluminum alloy castings with a steel insert cast into the top ring
groove. The skirts are solid and have cylindrical relief cuts at the bottom. Pistons have
three ring grooves above the piston pin bore and one ring groove below. Compression
rings are installed in the top and second grooves. The groove below the piston pin bore
contains an oil scraper. A center grooved and slotted oil control ring is installed in the third
groove which has six oil drain holes to the interior. Weight differences are limited to ½
ounce between opposing cylinders bays. Piston pins are full floating with permanently
pressed-in aluminum end plugs.
Figure 2-10. Piston Features
2-2.4.2. Hydraulic Valve Tappets
The hydraulic valve tappet (lifter) provides an interface between the camshaft lobe and the
remaining valve train. Lifters ride on the eccentric cam lobes, opening and closing the
intake and exhaust valves mechanically via push rod tubes and rocker arms, converting the
cam lobe profile into a linear movement for intake and exhaust valves actuation. The
hydraulic mechanism inside the hydraulic mechanism maintains zero clearance between
the valve and actuating components.
PISTON PIN
MANGANESE PHOSPHATE COATING
GRAPHITE COATED SKIRT
1
ST
COMPRESSION
RING
2
ND
COMPRESSION
RING
OIL CONTROL
RING
OIL SCRAPER
RING
Summary of Contents for IO-240-A
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