Cat 3208 Gearbox Noise
We were recently on a vessel carrying out some servicing and repair operations on a Caterpillar 3208 engine, and one of the tasks was to clean the engine mounted gearbox oil cooler.
Whilst we were doing that, we found that on the entry port the sacrificial anode was no longer in place, having travelled into the cooler and restricting the water flow.
This transmission oil cooler is located at the rear of the engine above the gearbox and is mounted in such a way that the oil in and out ports are both at the same height – halfway up the cooler.
As a result, any oil remaining inside the cooler when the engine has stopped drains back to the gearbox down to the level of the ports on the side.
When the engineers removed the cooler from the engine, approximately 120 ml was drained from it, but as the gearbox contained nearly 8 litres of oil, any oil remaining in the cooler would have little effect on the oil level in the gearbox.
Once the work was completed, we checked the oil level read as LOW, and the engine was run. (The operator’s manual for the gearbox states that when cold, the level should be on the low mark on the dipstick.)
After the initial run of the engine, the gearbox was topped up.
During that run, we heard a noise at regular intervals for 15-20 seconds and then the gearbox would run quietly – as you might imagine the client was quite concerned that there was now a new issue with the gearbox!
Our engineers recorded the engine running; whilst making the noise the output shaft was stationery and when the gearbox was quiet, the shaft was turning. This would indicate an issue with moving in/out of gear.
Click below to hear the cause of concern.
The recording was sent to the local agents for the gearbox for their opinion and we received confirmation that the noises heard from the marine gear are consistent with noises experienced in the past with this application.
They also advised that when at, or near, low idle and in neutral, the vibratory torque from the engine may exceed the light transmitted torque load on the gear teeth in the transmission.
The gears will separate and rattle back and forth between the normal gear tooth clearances (backlash).
With this information, our engineers reattended and adjusted the fuel rack travel to increase the engine speed.
As it turned out, one engine speed was lower than the other, and when we brought them together the engagement of the gears worked perfectly.
With the speeds matched correctly, the harmonics were synchronised.
Once this was complete and our engineers were happy, we took the vessel on a sea trial to maximum rpm, to provide further testing and reassure the operator that there was nothing to be concerned about.
The operator was happy that we took the time to demonstrate our work was thorough and conclusive and now has the peace of mind that his vessel is as it should be.