Engine Diagnosis and Service: Piston, Piston Rings, Connecting Rod, and Engine Balancing

1. Engine Diagnosis and Service: Piston, Piston Rings, Connecting Rod, and Engine Balancing Chapter 54

2. Objectives • Analyze wear and damage to the piston, piston rings, and connecting rod • Select and perform the most appropriate repairs to the piston, piston rings, and connecting rod • Explain the theory of engine balancing

3. Introduction • Complete rebuilt engine assemblies • Commonly installed in the industry • Sometimes a piston ring will break or an engine is overheated • Piston rings: replaced whenever engine is disassembled • Pistons are often reused • Connecting rods: do not usually require service

4. Piston Service • Important steps • Use a vice to hold piston and rod assembly • Remove compression rings with a ring expander • Top of the piston is cleaned on a wire wheel, with a scraper, or with an abrasive disc • Clean ring grooves with a ring groove cleaner • Use ring to double-check for correct groove depth • Check the top ring groove for excessive wear • Measure piston • Place to measure varies among manufacturers

9. Piston Service (cont'd.) • Replacement pistons • Designed to weigh the same as originals • Piston wear • Scuffing: caused by excessive heat • Four-corner scuffing: both skirts scuffed on edges next to piston pin

10. Piston Ring Service • Causes of piston ring wear • Leftover honing grit • Running engine with missing or damaged air cleaner • Contaminated oil fill funnel • Engine is rebored • Oversized pistons and rings are used • Check ring end gap • Before installing rings in a cylinder bore

12. Installing Pins in Connecting Rods • Pin press • Separates pressed-fit pins and pistons from their connecting rods • Reinstallation is done using a rod heater to heat the eye of the rod

13. Installing Rings on Pistons • First • Install oil rings • Second • Install the second compression ring • Third • Install the top ring

14. Oil Ring Installation • Most automobiles use three-piece oil control rings • Compression ring installation • Installed with identification marks facing up • Use a ring expander to install compression rings • Compression ring gap position • Manufacturers specify different gap positions

17. Connecting Rod Service • Important points • Be sure to keep rod cap rods in order • Upper and lowered pieces should be numbered • Examine all piston skirts • Connecting rod resizing • Pressed-fit rod bolts are pressed or pounded out • Small amount of metal is ground off the rod and cap mating surfaces • Rod cap is reinstalled and the nuts torqued • Rod bore is honed

20. Engine Balancing Service • Done by a machine shop or a balancing specialist • Reciprocating parts: balanced to weigh approximately the same amount • Rotating parts: balanced by spinning on a balancing machine • Heavy counterweights • Lightened by drilling • Internal balancing • Achieved by drilling holes on the counterweights

23. Engine Balancing Service (cont'd.) • Bob weights • Used when spinning crankshaft to simulate correct weight • Replacement piston balance • Critical in V-type engines • Balance shafts • Must be replaced in the proper manner to maintain balance

24. Advanced Balancing Information • Types of vibration • Primary vibration • Rocking couple • Secondary vibration • Types of imbalance • Force (i.e., static or kinetic) imbalance • Dynamic and couple imbalance