Onan generator raw water pump

[SilverSailor]

I have a 2014 R31S with the two ACs rather than the diesel heater option. I have the Onan MDKBH generator. As it's a bit of a pain to get to the raw water pump in this generator, I looked at options other than just the rubber impeller. I have installed a 110-volt March circulator pump with 8.3 gallons per minute flow. This pump is wired to the line side (not the load side) of the generator. This means that anytime the generator is running the pump is powered. If the main breaker trips the generator and the pump are still running. When the generator is stopped, either manually or by some fault condition, then the pump stops. I ran it with the rubber impeller installed for a while, and it ran fine but I didn't want to have the impeller destroy itself and put rubber parts into the raw water system, so I have removed the rubber impeller and It's operating well. As there is a water seal in the original raw water pump, I have left it the original pump plumbed into the raw water flow. While doing the wiring to make this modification, I realized that the MDKBH generator is wired as a single 115-volt output. The two poles on the power breaker are even jumpered together at the breaker. I was surprised to find out that the generator was wired as a large single source suppling 115 volts of the same phase. My question is: Is this option better than wiring it as a 220-volt source with two different phases of 115 volts? Just seeking better understanding of these options?

Also, it appears that the original raw water pump has sealed bearings on the shaft outside of the raw water pump housing and the shaft seal just seals the raw water pump housing. I'd like to change the hoses to bypass the raw water pump completely. This would mean that the whole original raw pump would be out of the raw water system and be just a means to adjust the belt tension. This would prevent any leaks into the generator sound proofing housing if the water seal of the raw water pump housing gives out. Anyone else have any real experience with modifying the raw water system like this?

 

[knotflying]

As a general question; how did you know the proper flow you needed from the auxiliary pump? Assuming that the generator is similar to the diesel, if there is too much water flow you could get water feeding back into the pistons. Also, with an engine driven pump the flow ebbs and flows with the engine RPM. In your case it is constant.

 

[SilverSailor]

I downloaded the service manual for my generator - Onan MDKBH. This showed the raw water flow to be 5 gallons per minute. I also found information, I can't remember where, that when the generator is running it's not possible to overflow the wet muffler. The exhaust pushes it out. So far, I'm more than pleased with this mod. I am planning on removing the raw water pump next spring to see if it's possible to verify that the raw water pump can be completely removed so the only thing that is left is the bearings on the pulley so it's only purpose is to adjust the belt tension. The only changes to the plumbing will be to move the hose that was the inlet to the original raw water pump to the heat exchanger. The original connection for this was the output from the raw water pump. It's just a matter of moving the hose 2 to 3 inches. If you've worked on this model of generator, you should be able to understandable what I'm describing.

 

[skipper207]

Chiming in with a side question.
I am trying to access my onan water pump, it does look like a pain. I have a 2017 C30, imagine the access is the same.
Do you need to remove the port side panel of the generator to access the pump? The top panel also? I don't want to create too much extra work for myself and would love any advice on accessing the pump.

 

[SilverSailor]

On my Onan MDKBH generator, removing the front cover and top cover and the side cover are required to access the raw water pump. For me, I find replacing the impeller requires removal of the whole pump with the v-belt pulley from the generator. And it's what is stated in the Onan Service Manual that I downloaded from the internet. Google "Onan Cummings service manual MDKBH". I found one that was a free PDf. It's well worth the effort. I hope this answers your question.

 

[Bobby P.]

Working on these generators often requires removing parts of the sound shield, with not much room to work.

I'd like to share a tip that has helped make sound shield removal a little easier. Dewalt make a 90 degree attachement for your drill or impact drive (I prefer an impact wrench) that makes removal and re-assembly of the sound shield much quicker.

https://www.amazon.com/DEWALT-DWARAFS-R ... th=1&psc=1

Good luck!

 

[SilverSailor]

Good idea! I use a 1/4" ratchet and socket to remove the sound panels. One other major problem with accessing the generator is limited access caused by the folding aft seat. I removed the hinges from the folding seat and the deck and ground off the ends where the hinge pin is inserted so I could make the pins removable. I screwed both parts of the hinge back together and pushed the pins back in, lubricated with silicon dielectric grease. Now whenever I have to access the generator or any other items on the transom I can tap out the pins and remove the seat for much easier access. The hinge is now a removable pin pintle and gudgeon sort of set up.

 

[skipper207]

SilverSailer - you're a life saver! I have the same model onan and found the manual with the search you suggested. Huge help. The whole process is a pain but better access than I suspected to be honest. I can appreciate why you altered those hinges, good idea.