Connecting Rod: Testing and Inspection

Power Problems


PISTON AND ROD ASSEMBLY





There are a number of power related problems including excessive oil consumption, smoke, blow-by and poor performance that can be caused by inadequate sealing between the piston rings and the cylinder walls. A blowby measurement can help detect the problem.





Verification of the damaged or worn component requires visual/dimensional inspection of rings, pistons and cylinder walls.





The cause of piston ring wear can range from wear over a long period of service to a dust-out in a short period of time because of poor maintenance of the air intake system.





During repair it is essential that the cylinder wail be de-glazed so that new rings will seat against the cylinder wall. Failure of the rings to seat can result in high blow-by and excessive oil consumption.





However, it is also critical that the cylinder walls be thoroughly cleaned after the de-glazing. Grit left in the cylinder wall will cause rapid wear out of the new rings leading to the previously discussed power problems.





Overheating of the engine from a loss of coolant will cause the cylinder to overheat resulting in seizure of the piston.





Improper maintenance of the lubrication system is the primary cause of reduced main bearing life.





Reduced oil pressure may be an Indication that bearings are wearing. If wear is allowed to continue, bearing clearances become excessive and the crankshaft will hammer on the bearings, causing a knocking sound.





A rod knock occurs when the engine is not loaded. Verify by first applying load and then unloading and listening for the knock.