Onan Micro Quiet 4000 Gas Powered Generator Won't Crank

[Bordercollie]

Has been starting and running for periodic exercise. Now tries, but won't crank, acts as if battery power is low. 13.1 volts at house battery with shore power, 14 volts with truck engine running. Tried emergency start and starting at the generator and starting with engine running. May be stuck at top dead center. Will check genset ground connection.

How do I get access and rotate piston past TDC if needed.

[falconbrother]

I had an Onan 4k on my motorhome. It had trouble starting, I eventually replaced the starter and that fixed it. I bought the starter on Amazon. My starter had gotten weak over time and I just didn't notice. The new starter spun the genset over much faster making it start easier. At times the old starter wouldn't spin the engine over and I would have to try several times.

I also had another issue with it where it would only start while holding the start button down. I replaced the control board and it fixed that.

[klutchdust]

Thanks JD. "klutch,

ONAN Operating Manual calls for taking the load off the genny for a few minutes before shutting down. Like idling your road engine can stabilize temperatures across several dissimilar parts like head and exhaust manifold. I expect ONAN wants some of the working heat load off piston, cylinder, valves.

When a small engine has come to rest at exactly Top or Bottom Dead Center, it can be a bear to budge it off of there because of the geometry of the crankshaft."

Now it makes sense. I should and will read up on my genset, thanks.

[Bordercollie]

Plenty of gasoline in tank, suspect corroded genset's ground connection has gotten worse. Other battery connections are clean. Will try rotating flywheel past TDC. Will post on what worked.

Thanks for inputs.

[j-d]

klutch,

ONAN Operating Manual calls for taking the load off the genny for a few minutes before shutting down. Like idling your road engine can stabilize temperatures across several dissimilar parts like head and exhaust manifold. I expect ONAN wants some of the working heat load off piston, cylinder, valves.

When a small engine has come to rest at exactly Top or Bottom Dead Center, it can be a bear to budge it off of there because of the geometry of the crankshaft.

SAR Tracker,

The Update was me, after going out to exercise our ONAN, finding a dead house battery, and checking for the crankshaft nut size while I was tinkering. CloudDriver mentioned his was hard to budge when stuck. Ours wasn't stuck just now and moved very easily with the short Craftsman ratchet and 9/16 socket.

We don't have an update from the OP yet.

[SAR_Tracker]

So did it end up being just a low battery, or was the TDC thing the culprit?

[klutchdust]

CloudDriver wrote:
I had a similar problem with our Onan MicroQuiet several years back. We had pulled into a gas station and shut down the generator without letting it run for a few minutes with no load to cool down. When we tried to start it later the starter clicked but it wouldn't crank at all. I removed the generator access cover, reached in and tried to turn it by pulling on the fan blades. No luck with that. Fortunately I carry a 3/8" socket set that had the right size socket for the bolt on the fan/flywheel. It took quite a bit of effort to break it free. Started right up with the starter after doing that and no problems since.

I'll never forget the no load cool down period again!

I am not familiar with a no load cool down and having to turn your gasoline engine to break it free, break it free from what? If your gasoline engine is locked up and won't turn you have some serious issues, how does heat lock up your engine preventing it from starting again? This is a new one.

[j-d]

UPDATES:

1. Socket Size is 9/16" with a snug fit and 14mm will also work

2. It's easy to get a socket in there on an ordinary ratchet

3. Our 4 YOA Walmart trolling motor battery 1 year warranty is failing

4. I was able to start the generator by clipping one of those little Lithium Ion start packs. Specifically a Stanley SmartStart

[SAR_Tracker]

I would add: before moving the flywheel, disconnect the negative cable on the battery. Murphy's Law (Anything that CAN go wrong, WILL) states that moving the flywheel will start the engine.

[DrewE]

I've just reached in with my hand and (carefully) twisted the fan blades on the edge of the flywheel. No idea what the big nut in the middle is for the Onan flywheel. Obviously one wants to take care to avoid starting it inadvertently.

[CloudDriver]

I had a similar problem with our Onan MicroQuiet several years back. We had pulled into a gas station and shut down the generator without letting it run for a few minutes with no load to cool down. When we tried to start it later the starter clicked but it wouldn't crank at all. I removed the generator access cover, reached in and tried to turn it by pulling on the fan blades. No luck with that. Fortunately I carry a 3/8" socket set that had the right size socket for the bolt on the fan/flywheel. It took quite a bit of effort to break it free. Started right up with the starter after doing that and no problems since.

I'll never forget the no load cool down period again!

[j-d]

Can't add much to the above, except I've found the Coach/House Battery has to be in TOP condition to crank that little ONAN. I know that suggests that Engine Running + Emergency Start, should crank it. Still wanted to mention my experience.

Taking this as Reminder to go exercise our genny.

Can somebody provide the Wrench Type/Size our OP should try on that Flywheel?

[gotsmart]

In the past when the house battery was too weak to start my Onan MQ4000 I would:
1) start the MH's engine
2) go back to the test panel
3) push down on the generator rocker switch to prime it
4) push up on the generator rocker switch to start it
5) turn off the MH's engine

I'm not sure why it works, but it does on my MH. YMMV


EDIT: had the "down" and "up" reversed

[DrewE]

Open generator shroud on the ONAN cover (with the two flip latches). You can reach the flywheel pretty easily from the left side; it's basically in line with the vertical baffle in the generator case.

Check the voltage at the generator when trying to crank, and in particular across the starter solenoid. It may be as simple as a bad connection there, or a loose control wire on the solenoid. Hopefully it's not the starter itself or a connection to it as you need to entirely remove the upper generator case, which generally means dropping the generator. On my Coachmen, it took me a good portion of a day to disconnect the necessary connections and drop the generator (to change out a broken starter).

[pastorbillv]

What's its fuel source? My generator gets its fuel from the RVs gas and the system stops it from starting when my RV fuel tank is below 1/4 full.

Other usual problem is enough fuel in the system. You have to prime the heaven out of small generators some times to get them to start.

Boy, did that take a long time to figure out.