Engine noise GX390

Noise that happens twice per revolution on my GX390 with pressure washer on it. Sounds internal to the engine. I’ve tried removing the pull starter to see if anything was hitting, then turning the motor over by the pump and it still makes the noise.

When cranking over with the electric starter or when it’s actually running you can’t hear anything (although the machine is pretty loud). Engine runs smooth. I’ve never run it low on oil, always check it before using.

Anyone seen this before? I’m just trying to avoid an engine tear down if I don’t have to.

When you remove the pull start did you try pulling the rope to see if it’s the pull start and not the motor?

Yes because I turned the motor over by hand from the pump end with the pull start removed and it still did it.

Gear or belt drive?

Direct drive

Does the engine have many hours on it?

Still does that with the spark plug removed?

No idea, I bought the machine used.


I have found out the problem. I started with the process of elimination, first removing the push rod from the exhaust side to see if it would go away (potentially linking the decompression mechanism), sound was still there.

I then proceeded to remove the camshaft itself, and voila, noise was completely gone. It turns out the noise is created by the backlash between the cam and crank gears…not much I can do about it, I threw it back together as is. The engine runs fine but the noise was bugging me not knowing what it was.