The main 4 components of a piston and connecting rod assembly are:
- Piston
- Piston Rings
- Piston Pin
- Connecting Rod
What TEMPERATURE and PRESSURE does a piston encounter in a running diesel engine?
Pressure - 2000psi (13789.5kPa…though current pressures are near 3k-4k)
Temperature - 3500F
Why is aluminum used for the construction of diesel engine pistons?
Aluminum is:
- lighter
- produces less engine vibrations
- 3x the heat conductivity of cast iron
- provides a bearing surface for piston pins
What is the main characteristic of a TRUNK TYPE piston?
The crown and skirt are manufactured as one piece
What are 5 main parts of a piston?
- Valve reliefs
- Crown
- Skirt
- Piston pin bore
- Piston ring grooves
- Dome
- Ring lands
- Oil holes
The purpose of CAM GRINDING the skirt of a one-piece aluminum piston is to:
Allow the uneven expansion in the piston pin bore area
In a piston, what purpose do the holes in the oil ring groove serve?
To allow oil to freely move when lubricating the cylinder wall.
Ring groove inserts are used in aluminum piston construction to:
Reduce wear in and reinforce compression ring grooves
What is the purpose of the slipper skirt piston design?
To provide clearance between the slipper skirt and crankshaft, when the piston is at BDC
What is the advantage of using a two-piece piston design?
- The piston head/crown is made of strong material to withstand high heat and pressure
- Combustion forces are transferred directly from the crown a bushing a piston pin assembly
- Piston crown motion is reduced
- Direct loading and a greater pin bushing area reduce bending stress on the piston
What is a semi-floating piston pin?
A pin that freely rotates in the piston, but is fixed to the connecting rod
What is the most common type of piston cooling used in a medium/high-speed diesel engine?
Oil sprayed through a piston cooling nozzle
What are the two types of piston rings used in an engine?
- Compression rings
- Oil control rings
The purpose of piston ring end gap is:
to allow clearance for ring expansion (from heat)
What 3 factors help a compression ring create an effective seal along the cylinder wall?
- Oil film
- Ring tension
- Cylinder pressure
The purpose of an oil ring expander is to:
Provide the needed ring tension for oil control
The two main advantages of a KEYSTONE ring over a RECTANGULAR ring are:
- Stronger ring lands due to the tapered groove
- Self cleaning (greater resistance to buildup)
Chromium plating is used on compression rings because:
It increases heat transfer and reduces friction
What is the purpose of a connecting rod?
It forms a link to transfer combustion force from the piston to the crankshaft
Identify 5 parts of a connecting rod:
- Nut
- Balance pad
- Thrust face
- Rod bearing bore
- Parting line
- Beam shank
- Piston pin bushing
- Piston pin bore
- Bolt
What are four methods of maintaining connecting rod and cap alignment?
- Fracturing
- Dowel pins
- External markings
- Shouldered bolt
- Tongue and groove joint
- Serrated joint
Identify two connecting rod designs:
- Straight cut
- Bias cut
- Fork and blade
- Articulated
