Nissan GX1000 Generator - rod knock / other issue?

[kd5byb]

Good afternoon all,

A couple of months ago I picked up a Nissan GX1000 generator that dates from the mid-1980's the best I can tell.





It is a four stroke, 3,600 RPM unit rated at 750 watts AC output and has a 12V DC output of a rating I cannot remember. After cleaning out the fuel system, it starts, runs, and generates fine. Given how clean it is internal to the generator head and other places where dirt would normal accumulate, I doubt it has more than 50 or so hours on it. Certainly it sat someplace where it wasn't given a lot of love as you can tell with the rust on it.

As to noise level, it is probably on-par with a Honda of similar size. You can have a conversation standing right next to it running without raising your voice.

The only thing that bothers me is that when its running at load, it has a metallic buzzing/knocking sound that seems most prevalent on the side of the unit with the muffler. Listening to the engine crankcase with it running via a length of tubing stuck into my ear, I don't hear the buzzing/knocking sound.

The noise is not influenced at all by motor oil choice. It does it with straight SAE 30 as called for on the decal and is no less loud with synthetic 5W-40 which is in it right now. I've changed the oil a couple of times now, and there are no metal chips in the oil, and it comes out pretty clean.

So...I'm curious to see what other people think that the noise might me? I've looked for the obvious - no loose sheet metal, no loose bolts, etc... Below is a youtube video showing it running at idle and with a 500 watt load from a halogen shop lamp.

YouTube Video - Nissan GX1000 Generator Running with and without Load

Curious what y'all think?

thanks much,
ben

 

[PolarisX]

We have one of these we take drag racing at the hobby shop. Looks EXACTLY the same and makes some awful noises, but hasn't quit in years.

 

[JTK]

Cool little portable gen!

Is it over-head valve? Checking valve lash or anything loose under the valve cover wouldn't hurt. Could also be something loose in the muffler, or in the housing/enclosure of the machine.

I know my little ~1600watt Coleman Powermate powered by a flat-head briggs vibrates so badly, it makes noises due to the vibes. I've had nuts/bolts vibrate out and outer panels fall off the enclosure.

 

[bioburner]

Have a very old Honda that was up to the same [censored]. Took to small engine shop and they said it was bunch of carbon and cleaned it and still use it to charge batteries way out in the field. Even forgot it once and drove over it with the 4 wheel tractor till the only thing above ground was the handle. New tank and still in use but not as easy to start. But considering it was purchased in 78 I don't mind

 

[Trav]

I would check the valve adjustment first, i am not familiar with the engine but its always safe to start with the basics. Next step I would uncouple the generator from the engine to better isolate the noise.

 

[meep]

another pull-head-for-carbon vote, with valves next.

 

[kd5byb]

Evening all,

Thanks much for all the replies! I'll be pulling the head and checking the valves the next time I get a chance.

Thanks again,
ben