Failure Analysis of Piston Knocking in Diesel Generator Set

A diesel generator set equipped with TY320 bulldozer has cavitations in the cylinder and cooling water enters the crankcase, which makes the diesel generator set unusable. Overhaul the diesel generator set. Disassemble the diesel generator set and conduct technical appraisal after cleaning. According to the appraisal results, replace the crankshaft bearing bush, connecting rod bearing bush, connecting rod copper sleeve, piston, piston pin, piston ring, cylinder, intake and exhaust valves and fuel injector with new parts. Recalibrate the PT pump and handle the intake and exhaust valve seats. After assembly, the diesel generator set was tested and operated well. After a day of no-load running in, it was put into use.

The initial test run of the diesel generator set was basically normal. After 100 hours of operation, there was an obvious knocking sound, and the crankcase had serious blowby. Upon inspection, the knocking sound came from cylinders 3 and 4.

Fault Finding and Analysis

Firstly, we suspect the quality of the product, and for this reason, we need to seek technical evaluation from suppliers. There are no issues with the quality of the accessories. Check the oil cooling nozzles of cylinders 3 and 4, they are normal.

During the overhaul of the diesel generator set, the adjusting pad of the cam follower assembly was replaced, so it was suspected that the injection timing was late. Use a tool specifically designed to adjust the injection time to carefully check that the injection timing is correct. Suspect that there is a problem with the atomization of the fuel injectors for cylinders 3 and 4, and after inspection, it is normal.

Opening all cylinder heads for inspection, it was found that the other four cylinders were working normally. It was found that there was a problem with the third and fourth cylinders, and the top of the piston was burnt blue due to high temperature. The periphery of the top of the piston of the third cylinder was severely strained, the piston ring was slightly bitten in the ring groove, the surface layer of 1cm in the middle and upper part of the inner wall of the cylinder liner fell off, and the piston of the fourth cylinder was slightly strained. Checked the cooling channels of the 3rd and 4th cylinder blocks and cylinder heads, and no issues were found. Therefore, it is suspected that there is a problem with the cylinder heads of cylinders 3 and 4. There is a fuel delivery passage in the cylinder head of NTA855 -- C360 diesel generator set. The diesel delivery passage in the cylinder head of the third and fourth cylinders is pressurized and tested. It is found that fuel seeps from the air inlet crack, so it is judged that there is a crack in the air inlet of the third and fourth cylinders.

Under the pressure of PT pump, the fuel of the diesel generating set enters the intake port of the diesel generator set from the crack of the cylinder head, and is brought into the cylinder with the intake air flow and attached to the inner surface of the cylinder liner and the top surface of the piston. These fuels will form 'deflagration', causing a knocking sound when the gas pressure inside the cylinder exceeds normal pressure. At the same time, the excess fuel washes out the cylinder wall, damaging the lubricating oil film on the inner wall of the cylinder, causing dry friction between the piston and the inner wall of the cylinder, causing cylinder pulling.

Dingbo Power was founded in 2006 and is one of the earliest manufacturers of generators and diesel generator sets in China. If you want get more information, please feel free to send email to sales@dieselgeneratortech.com we will pay highly attention on your question.