Kubota L3902 engine noise

DiWil35 · Jan 6, 2024

I have a Kubota L3902 HST with 200 hours, the tractor runs perfectly fine but I notice a sound from the engine and wondering what it could be.

I revised this post

The sound I am hearing from the engine is a tapping sound that is slightly deep, it isn't loud like a banging sound but it is enough where I can notice it. It is most noticeable when the engine is cold during a cold start but goes away when the engine warms up.

There have been times when the engine is still warming up such as moving the tractor or using the mower I would notice the tapping sound from the engine suddenly disappear.

Any ideas? Has anyone every noticed a engine noise like this before?

MTGreen · Jan 9, 2024

What kind of frequency with the tapping sound?
WAG is solid lifter slop & may be reduced with valve adjustment.
Is the engine over-full of oil?

Another thought is using a long handle screwdriver up to your ear and touching various (obviously stationary) parts of the running engine or using an engine stethoscope to localize the sound to a particular engine area

DiWil35 · Jan 10, 2024

The frequency is directly linked to the rpm of the engine, I want to say the noise seems to be on the ignition or power stroke of one of the cylinders where when a cylinder fires I hear a tap.

Engine oil is at a normal level or right at the full mark.

I used a wooden rod and listened to different places on the engine. The loudest area was the fuel injector pump, particularly near where the house exits the pump I can hear a loud sound. Around the bottom of the engine where the oil pan is I hear a slight tick sound but it isn't that loud.

I recorded mp3 audio of the tapping noise from the engine but I haven't figured out how to attach it to this post

MTGreen · Jan 10, 2024

I would vote for the easy bit first adjusting the valves. If that doesn't fix the noise then you can go down the rabbit hole of piston slap etc.

Maybe others can chime in here as well