Onan Cummins 8KW Genset Issue

[Terry Cox]

Help! Our Genset has about 450 hours of use. Always starts and runs well. Two weeks ago when I started it no water came out of the exhaust. Began trouble shooting the issue starting with the obvious. Sea water strainer clear. Impeller replaced in 2013, but pulled the pump cover off and found a missing vane. Had a spare so replaced and still no water. Grrr.

Both input and output hoses seem clear. Disconnected the pump output hose to see whether the pump was bringing water in. Nope! When I did this the engine spit out two vanes, so the systems has no clogs. Replaced the sea water strainer cover gasket. Nope! Primed the output hose. Nope!

At this point I've run out of options. The impeller is the correct one for this engine. Sea water flows in from the intake hose. I can also blow air out the intake hose and the discharge hose..

I'm open to any ideas and really appreciate your input. Perhaps I've overlooked something.

 

[Mechone]

If your shaft seal is gone on the pump you will suck air and no water. Also you want to lap the pump cover on a flat surface with sand paper going in a figure 8 turn the cover in 1/4 turns until you remove the wear or replace the cover .

 

[Johnb]

The old "shaft is turning but the impeller is not".

 

[Terry Cox]

Impeller and shaft turns with the engine. Onan Cummins has no reference of a shaft seal. I'll press them again. Thank you for your input.

 

[Mechone]

Impeller and shaft turns with the engine. Onan Cummins has no reference of a shaft seal. I'll press them again. Thank you for your input.

You should have 2 seals , one to keep the oil in the engine ,if it's direct drive off engine and a second one to seal water from coming out of pump. One on engine lip in, one on pump housing lip out. When the pump one goes, you will suck air along shaft and not draw water. Also if the internal clearances become too big ,that's why you must remove impeller wear on cover and or replace it. Is the removable bump on the bottom on the pump, the one that compresses the impeller as it goes around . On most pumps these are replaceable and are held in with a screw off pump housing.

 

[Terry Cox]

You should have 2 seals , one to keep the oil in the engine ,if it's direct drive off engine and a second one to seal water from coming out of pump. One on engine lip in, one on pump housing lip out. When the pump one goes, you will suck air along shaft and not draw water. Also if the internal clearances become too big ,that's why you must remove impeller wear on cover and or replace it. Is the removable bump on the bottom on the pump, the one that compresses the impeller as it goes around . On most pumps these are replaceable and are held in with a screw off pump housing.

Yes. Cummins refers to that part as a cam; made of bronze, it appears, and has about 450 hours of use. It still seems to do the compression as I observed the impeller spinning.

Waiting for a call back from a local Cummins dealership technician to determine next steps. The Cummins tech support guy back east somewhere was unable to provide next steps and referred me to the local distributor. He could not tell me whether there was a shaft seal that needed replacing. His only reference point was a kit that included an impeller, gasket and cam. Those I replaced, except for the cam, with my on hand spare.

 

[Terry Cox]

Still no worky. Had a long conversation with Jeff from our local Harbor Marine shop, He gave me several suggestions, most of which I've already tried, but some I need to confirm. A new pump is $600, but odds are not likely the problem with only 400 hours. No replaceable shaft seal, according to Jeff. The spare that I used was purchased in 2013. He told me that the impeller material does not age very well, so will plan on installing the one I just purchased. He also told me to check the width of the new impeller. It should protrude about 1/32" past the housing to insure a good seal. He said that even though we have the correct part number, the impeller may be of the wrong size. Will plan on replacing the cam at the same time. Also replaced the seawater screen cap seal. Running out of options.

 

[Mechone]

Every pump has to have a seal on shaft . Who makes the pump . Johnson, Jabsco, usually on the cover

 

[Terry Cox]

A few more troubleshooting steps to take this week.

1. Test whether the shaft seal has failed.
2. Confirm the pump brand.
3. Inspect whether the new impeller clearance is correct.
4. Do a prime test whether the pump can draw water from the same level as the pump.

If all that checks out, install the newest impeller, prime the system and test whether I have solved the problem. It has to be some simple, overlooked issue, or made some wrong assumptions. If all the above fails, perhaps time to hire a marine tech.

I used to trouble shoot Phantom problems far more complex than this. Bound and determined to fix it, one way or another. Jeff, at Harbor Marine in Everett, has been very helpful in stepping through various issues that may be causing the problem.

 

[smokey73]

Not sure where the pump suction line runs but is it possible you have a split in the hose above the water line so that when the valve is open there is no water leaking in but when the pump runs it sucks air? Just thinking of ways to lose suction. Even a small split might be enough. Could you try hooking up a vacuum hose like from a shop vac and see if you can suck water from the intake valve to the suction side of the pump?

 

[Terry Cox]

The intake hose from the seawater strainer to the pump is new; replaced it last year. Thanks for the input.

 

[Mechone]

Ok I had a buddy with same problem after I rebuilt his pump , check to make sure the rubber o-ring is on the sea strainer his went missing and he was suck air

 

[Terry Cox]

Ok I had a buddy with same problem after I rebuilt his pump , check to make sure the rubber o-ring is on the sea strainer his went missing and he was suck air

No “O” ring here, just a flax seal. Still working, but replaced it anyway, which did not solve the problem.

 

[Terry Cox]

Yesterday was my go to day. Onan Cummins Genset now worky. I’ll do a complete write up in a few days. A very frustrating problem now solved. Some know the meaning of the term, a common denominator. Well that was what it turned out to be. After eliminating all the possibilities, the final fix was...

 

[Terry Cox]

A few more troubleshooting steps to take this week.

1. Test whether the shaft seal has failed.
2. Confirm the pump brand.
3. Inspect whether the new impeller clearance is correct.
4. Do a prime test whether the pump can draw water from the same level as the pump.

If all that checks out, install the newest impeller, prime the system and test whether I have solved the problem. It has to be some simple, overlooked issue, or made some wrong assumptions. If all the above fails, perhaps time to hire a marine tech.

I used to trouble shoot Phantom problems far more complex than this. Bound and determined to fix it, one way or another. Jeff, at Harbor Marine in Everett, has been very helpful in stepping through various issues that may be causing the problem.

Did the above test yesterday.

1. Disconnected the output and input hoses. Plugged the input port with my finger.and blew as hard as I could into the output hose. Did the same with the output port. Zero air leakage.

2. Pump brand is Oberdorfer.

3. The 2013 impeller, although the right part number, did not extend past the housing by 1/32”. The new one that I purchased a few weeks ago does, even though the diameter and vane width we’re the same. So what I ruled on was that the bronze impeller bearing was incorrectly seated when it was made, or the wrong part.

4. Did not do this test, since the new impeller worked.

Primed both hoses, started the engine and let her pump water for five minutes. All good. Shut engine off and let set for a couple of hours to test again. Test was successful.

Since I have no paperwork on the 2013 impeller, nil odds of Onan standing by their product. Harbor Marine will give it a try, but I’m not going to hold my breath on that one.

 

[Michael Davis]

Good to have it fixed. Some things can be so frustrating.

 

[MitchM]

a great diagnosis and checklist for anyone w an onan gen ... thanks !

 

[All U Get]

I start with the hose connecting to the HX, I hold the hose in a bucket while the wife starts the engine. Getting a good flow eliminates strainer/pump issues. If it has little or no water, do what you just did. If you had plenty water flowing, there may issues with the HX, mixer elbow, or beyond.

 

[Terry Cox]

After solving that problem, another popped up. Left home for a few days on the water knowing that I had a working Genset. On day two in Eagle Harbor it was time to start the Genset to heat water, charge the house bank and do some cooking. She started right up. Went on deck to make sure she was pumping water, check. Then she decided to shut down. Tried restarting, but no luck. Hmm.

Next day I headed back home to begin trouble shooting. Sounded as though the Genset was not getting enough fuel, so perhaps time to replace fuel filters. Log book said it was 2013 the last time to replace Racor filters. Engine filter looked pretty clean, but replaced it anyway. Racor another matter. Some water and almost black. Primed both and tried four times to start with short cranks. Sputtered some, but no luck. Waited a few minutes while I replaced the main engine Racor filter. It was in worse condition. Also some water and very dark in color.

Tried a fifth crank and she tried to start. I suspect a bit of air in the system. Tried one more time and she started and ran for fifteen minutes without hesitation. Shut her down and waited about an hour before restarting. Fired right up and ran for ten minutes without a hitch. Problem solved. Must do a better job in draining any water from the Racor filters each season. Only about 100 hours on the Genset since replacing the filters.

Next on the list is to change engine oil and filters, and replace the main engine seawater impeller.

 

[jssailem]

Thanks Terry. Good info on a Diesel engine be it a generator or an auxiliary power plant.
Back on the water for you. At least as long as the kids are being home schooled.