ONAN 20KW (Cummins) will start but...

[Osprey69]

...only by holding down start toggle and waiting for a "clunk" behind panel (about 2-3 seconds). I think this is new so what might need replacing? Generator is 1985 model year (still works great otherwise!). Thanks in advance!

 

[O C Diver]

There's a start circuit that lasts less than a minute. The circuit allows the generator to start without oil pressure. Once past the start circuit, low oil pressure, high coolant temperature, or low DC voltage can shut the generator down. My guess is that you have a sensor or relay issue relating to the start circuit.

Ted

 

[Lepke]

I have a similar Onan. Once you release the start toggle, does the engine stop? Temperature and oil pressure safeties are bypassed while pressing the toggle. One of the sensors could be bad, it could be a connection, check your grounds. The amps needed for starting can sometimes spark thru a bad ground, but small amp needs don't. Strange but it does happen.

 

[BruceK]

Could the "hold" on the start solenoid, which keeps the solenoid plunger engaged and fuel flowing after starting, be defective? On my 6.5 Onan, you could see the solenoid with the front cover removed. If it is the cause, replace the solenoid. Check eBay(as well as Cummins) for a replacement.

 

[Osprey69]

Thanks for the suggestions. Will report back.

 

[luna]

Does the genset actually start after you hear the clunk and then after you release the start toggle does it continue to run so that you can bake the pie in the oven?

 

[Osprey69]

Luna...yes and yes.

 

[luna]

Luna...yes and yes.

I kinda thought so by the way that your Title flows into the body of your post. This to me would rule out any of the overtemp sensors (they don't clunk anyway) simply because the pie gets cooked.

If your genset is powered by the same engine as my 1995 20 kW Onan, it is a Kubota 2203. You may be able to find the engine serial number that is stamped into the engine block by removing some of the paint on the horizontal portion of the block that is proud of and forms the mounting surface for the fuel injection pump. Serial numbers are really helpful when buying parts from your local engine manufacturer's dealer.

If my genset developed this condition (my starter turns instantly upon toggle switch activation) and I was convinced that this is a new behavior, I would remove the clasp mounted sound shield panels and:

- As I have a dedicated start battery much like a car, I would record the battery voltage with the genset at rest for a day or 2, at the battery and at the starter. I would also record it again after 5 or 10 start attempts, just to get an indication of battery capacity.

- Try to find the clunker using sound and feel while repeating the start process, multiple times.
Prime suspects include the starter solenoid (the small can shaped thing mounted on the starter motor), the stop solenoid (another can with a rod that moves sticking out the end) which should really be called the run solenoid as it operates to allow the engine to run, and the electric fuel pump, a third can shaped device that is mounted just above the fuel filter can.
All of these are on the service side of my engine.

-Once I had identified the clunker, even if it's something other than my prime suspects, I would hook up a set of jumper cables from a known good battery and the start battery and see if that makes the delay/clunk go away.

The fix depends on the culprit, but it could be as easy as a good clean up, lubrication and/or adjustment.

Further insight/ideas may be obtained by having a read through or taping into the knowledge on the Smokstak website which specializes in things that were built in a simpler time.

Hope this helps, use your common sense and good luck with whatever path you choose.

 

[Osprey69]

Luna...thankyou for your thoughtful reply. The clunk is coming right behind the start toggle. So it is one of those switches or solenoid type thingy...

 

[luna]

It is likely that the design of your 1985 control system is vastly different than my 1995 control system simply due to the development of cheaper/better components during that time, so I can't comment on specifics.

If I was to shut off all power to the genset (both dc and ac) and remove the lid from the control box I would likely find the electrical schematic drawing on the underside of the lid. Take a picture of it while it's off.

I would then with the duct taped restrained lid covering all of the components in the control box except those right behind the start toggle, using a 1' long +/- piece of unreinforced 1" vinyl tubing as a stethoscope, turn on the dc only and listen for the clunk on each component while I ran the start routine.

It's likely a relay going bad and they generally just push into a socket in the control box. If I removed the relay it should have a name like Bosch or Panasonic and a number on it. Replacements should be easy to find on the net.

 

[Osprey69]

Luna...wow great suggestion. Thank you!