Onan RV QG 4000 Mechanical Issue and No Start

[Lumpty]

6 year old 4kw Onan Spec L. 920 hours (lots of dry camping). Oil, plug and air filter regularly changed, generally 2x annually, along with intermittent oil level checks.

Back late winter, it had an issue where a worn rocker spun 90 degrees on the stud, closing the exhaust valve and dropping the pushrod off the cam. Engine shut down same as being switched off. Apparently bad parts, rocker or nuts, when built. Replaced valvetrain hardware (stud, rocker, adjuster nut and lock nut). Pushrod still straight as an arrow. Bumped starter and all looked good. Valve cover back on and no start, blowing white smoke. Plug comes out wet with fuel, and there is spark to the plug. Did a compression test and only get 95 psi. I know earlier Onans had a compression release system, but I see nothing in the manual that this relatively late model version still does. Do not have a leakdown tester and don't really want to spend $100 on one if I don't have to.

The wildcard here is when I went back into the enclosure to dive into the valvetrain, there was a mouse wandering around in there that may have eaten through something not readily seen from the service door. Kind of hoping that my be the reason for my no start, but all the wiring I believe is on the front of the unit and no obvious evidence of things chewed though.

Before I drop this thing out the bottom of the compartment and tear into it, anything else obvious and easy to get to to check? And speaking of tearing into it, does anyone know if the engine on this is interference? Wondering if somehow when the rocker spun the engine went out of time and bent the exhaust valve.

[Lumpty]

A few of other "symptoms":

When cranked it initially acts like it fires up for fractions of a second.

I didn't think much of it at the time, figuring I'd just overfilled the oil, but the last air filter change the element came out soaked.

And I think the rings are fine. It really only has ever consumed a small amount of oil, maybe needed a 4 oz. top off between changes.

[WILDEBILL308]

Before dropping it. What you described sounds like it was flooded. Try cranking it with the plugs out to remove excess fuel then put the (dry or new) plugs in and see if it will start. While the compression is a little low it isn't a high compression engine. Let us know what you find.
Bill

[Community Alumni]

Until the motor starts and reaches operating temperature, all that smoke you see is uncombusted fuel and lubricants. 95 PSI compression tells us that the valve train is working, although the timing is not certain. You're getting Spark, but the sparkplug is getting wet. Maybe there is flooding due to a carburetor float sticking? Try cutting of the fuel supply and try starting with what fuel is in the bowl, maybe with the help of ether sprayed into the carb. If at that point the motor is showing signs of life, you can reconnect the fuel and proceed from there. My RV generator experience is with diesel mostly, the bulk of my gasoline/LPG experience was on the job at the phone company where those Onans absolutely had to start 24/7 365. Once the generator failed in a similar fashion as yours leaving me aloft in an aerial lift. Fortunately, there is a backup 12V electric hydraulic pump for such events. Unfortunately, without power for the air compressor, lights, heat and ventilation to the adjacent utility hole (manhole for you old timers), another truck had to be brought in. The rebuild revealed a worn valve train including push rods and carbon buildup (we used bulk fuel from Petro-Swill).

As far as suspected low compression, spritz in a bit of motor oil into the cylinder prior to doing a compression test holding the throttle wide open. A significant increase in pressure will indicate worn piston rings. That test is more telling once the engine has been running a bit and warmed up.