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Old 11-17-2018, 02:21 PM   #1
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Default Partial overhaul of an Onan 2.8 generator

Partial overhaul an undermount generator (part two)

I have an Onan 2.8 Microlite KVFA series J that would not crank. I had to drop the generator to diagnose the problem (See this post that details how to remove the generator).

Before you begin get a copy of the service manual and parts manual. They are available here. Make sure you have the correct model number for your generator.

Luckily, I did not have to take my engine or generator section apart, but I did have to remove it completely from the mounting base pan, which was extremely rusty.

The problem was a broken wire on the starter relay/solenoid. Once I took the cover off, I evaluated each component to decide whether to repair or replace each part. My generator is 18 years old and had 179 hours on it. Because it is an undermount unit, it is exposed to dirt, rain and moisture. The bottom mounting base pan was very rusty as were many of the exposed screws, bolts and nuts. I decided to replace most of the hardware with stainless steel parts where possible, as well as genuine Onan hardware and treat the mounting base pan with rust encapsulator.

Once I fixed the broken wire, everything worked. I decided to replace the following parts: All parts were available directly from Onan.

1. Muffler because it was rusty and had a broken weld
2. Starter relay/solenoid due to a rusty terminal stud
3. Fuel pump and its associated end fittings and the metal fuel pipe.
4. Various nuts, bolts and star washers, and some Onan specific hardware
5. Fuel filter and fuel line
6. Spark plug
7. Air filter
8. Four of the vibration isolators (rubber mounts)

Fuel Pump

When you buy the fuel pump it does not come with the top fitting (a 90 degree brass fitting with a barb end for the rubber fuel hose) or the bottom fitting (a brass fitting that accepts the nut that holds the metal fuel tube.) Also, the metal fuel tube that connects to the rubber fuel hose from the tank needs to be purchased. (expensive) The tube appears to be a metal brake line with a flair on one end and brake nut attached. The other end has a small bulge to hold the rubber fuel line. (See picture below)

Starter Relay/Solenoid

There are two large studs on each end where the power comes into the unit. I decided to replace the whole unit because it is a wear item (solenoid) and the studs were showing some rust.


My muffler has some rusted welds and the pipe from the exhaust manifold was loose where it entered the muffler. Onan has a new design that fit fine, however, it is very expensive.

Vibration Isolators (rubber mounts)

The generator is supported by four rubber mounts, (two different styles). When I removed the generator from the mounting pan base, one mount was completely missing. The other three are a different design and are attached to the mounting base pan by a small hex nut. This nut threads onto a stud, which goes into the rubber, and another Onan specific fastener that attaches to a removable stud. This stud screws into an extension on the bottom of the engine and also holds an oval metal piece, which supports the other end of the rubber mount. The upper end of the rubber mount has a small metal extension that fits into a hole in the engine. (See picture below)

When I tried to remove the small nut on the bottom of the mounting pan base, it was rusted and turned the stud, which broke the rubber. Only one nut came off the stud. Even if I had successfully removed the rubber mounts, I would still replace them due to their age and the fact that they are located in a hot environment right under the engine.

Removing the mounting studs

The three rubber mounts are expensive ($26 each) but they can be removed without breaking the rubber. You have to access the bottom of the mounting pan. First I drained the oil, than put the unit on its side on blocks. Now I had access to the bottom of the mounting pan base and the three hex nuts that hold the rubber mounts. There are also three, large Onan specific fastener surrounded by three large rubber spacers. The procedure involves removing the Onan specific fastener from the stud first. This takes a Torx 50 bit. Once removed, you use a deep socket to remove the stud from the bottom of the engine. The rubber mounts are now free from the engine and will stay attached to the mounting pan base at this point. Later, you can work on removing the hex nut from the bottom of the mounting pan base. Hopefully it will come loose and not break the rubber isolator. Inside the mounting base pan at the bottom of the rubber there is a metal disc. It is possible to hold the disc with a pair of pliers and then undo the hex nut from the bottom.

Once all three studs are removed, as well as the fourth rubber mount (a nut on the bottom of the mounting base pan and another nut on the top that attaches to a part of the engine), the unit is almost ready for separation from the mounting base pan. The metal end plate on the left needs to be removed and is held on with two screws on the bottom of the mounting base pan. The grounding nut (front left) that holds the ground wires to the mounting pan base needs to be removed. Several wire connector plugs need to be undone as well as several wires attached to various lugs. Remove the two screws that hold the control panel and disconnect some wire lugs, 5amp fuse holder and the large wire connector plug for the control panel. Remove the spark plug terminal and remove the ground strap from the rear of the engine that connects the engine to the mounting base pan. Take pictures and label your wires.

Foam insulation

There are two pieces of foam to help the airflow through the case into the fan. One is between the mounting base pan and the bottom of the end plate. Mine was still intact. The next was on the round base that houses the fan. It goes between the black end plate and the round base. Most of my foam was missing and crumbly. I put a new layer of closed cell foam. When you do this, make sure that it fits tightly against the black plate when it is in the final position. I had to build up the foam to about ½” to get a tight fit. This is very important for proper airflow.

Testing components

The service manual has a comprehensive diagnostic procedure for the components.

A very detailed Trouble Shooting Guide is also available on line from Flight Systems ( They also make aftermarket control boards for the Onan units that are cheaper than the original unit.

Carburetor cleaning

Some of these carburetors are an EPA version and are tamper proof. They have no adjustment for air/fuel mixture, just an altitude adjustment. Sometimes the bowl can be taken off from the bottom screw and then cleaned. The holes in the jets are very small and can easily get clogged. There is lots of info on the internet about these carburetors. From all my reading, I learned that you cannot tune the carburetor by ear. It will run smooth if you fiddle with it, but the carburetor controls engine speed which controls generator output and it must be measured in a specific manner (see the next section)

Seafoam gas treatment is commonly used to reduce the build up of the gas varnish, which will clog the holes. If your carburetor surges, first change the fuel filter then run some Seafoam through it. Mix one can of Seafoam with two parts of gasoline. Warm up your unit, let it run for about 10 minutes (it will run rough and smoke a bit), shut off the unit and let it rest, run it for 5 more minutes and then run your regular gas through it. Hopefully it will be smoother.

Engine and generator adjustments

Read the Onan service manual for the procedures. It states, “The governor controls engine speed which directly affects the generator voltage output and frequency. An increase in engine speed will cause a corresponding increase in voltage and frequency. A decrease in engine speed will cause a corresponding decrease in voltage and frequency. The governor maintains a constant engine speed under changing load conditions so output voltage and frequency will not vary. “

The procedure is to set the engine speed and governor adjustments so when the engine is both under a no-load situation and under a load situation it falls within a definite range. There is a speed adjustment screw and a governor sensitivity adjustment screw. The manual states, “With unit operating at no-load, adjust the speed adjustment screw on the governor linkage to obtain 62.5 + 0.5 Hz, at between 120 and 126 volts on 60 hertz units. Then use the governor sensitivity screw to give the closest regulation (least speed and voltage difference between no load and full load) without causing a hunting condition.”

When the generator is being tested and adjusted, you must have a multi meter that measures Hz or use an Electrical Management System (EMS unit that functions as a surge protector and electrical diagnostic unit). I use a Progressive Industries unit that shows Hz and volts. You must also connect an electrical load on the generator. I connected the three AC wires (white, black and green) to a standard receptacle in an electrical box. This receptacle can then be used to connect the load and to measure the frequency (Hz) and voltage. I use a space heater rated at 1500watts. Once you get your generator running smoothly, connect up the meter or EMS unit and plug in a load device. Then turn the screws until you get the values as specified above. (See picture below)

Insert diagram

Generator connections when the unit is removed

If you want to test the generator once it is out of the RV, you will need to set it up. I placed my unit on a small moveable dolly with casters so it could easily be moved. I put the unit on blocks because it was not installed on the mounting base pan. If it doesn’t crank, check your grounds. The following connections need to be activated..

12V power from a battery- I removed the positive and negative cables from my RV and then used jumper cables. There should have been a positive cable that you previously disconnected. The negative jumper cable can be connected to a screw attached on the mounting base pan.

Ground wires-If your unit is still not attached to the mounting base pan, you will need to connect several ground cables from some of the components. It should be noted that you need to have excellent contact between the ground wires and the engine and mounting base pan. Clean the wire end terminals and use new star washers. I use a multi-meter to check connections as I assemble the components. I also used an anti-corrosive spray or just coat the connections with a dielectric grease or silicone paste. This will help to prevent corrosion. These are the grounds connections.

1. Four wires from the wiring harness (left front next to the end plate). These
wires attach to a stud attached to the bottom of the mounting pan base.
2. Coil (a small blue box with a small black wire)
3. Engine block
4. Fuel pump.

I used some wire and alligator clips for a temporary set-up.

120V outlet-I just connected these wires (white, black and green) to a standard receptacle in an electrical box. This will be used to connect the load and to measure the frequency (Hz) and voltage.

Fuel line-I used a ¼’ inside diameter rubber fuel line that went into my gas can. If you are replacing the fuel line from the fuel pump to the fuel filter, make sure you get fuel hose rated for ethanol.

Fitting the top cover

The green fiberglass cover needs to be fitted so the black end plate on the left fits into a groove in the cover. If you lower the cover and the left side does not go down all the way, the end plate is probably misaligned. The front of the end plate rests against a raised section, the top fits into a double-sided groove and the rear of the end plate also fits into a groove. I needed two people to get it aligned. You have to fit the cover over the connector that holds the AC wires, which tends to work against you efforts, as well as the positive wire and remote start wire. I found I had to tilt the cover first to get it over the connector, keep the cover straight from side to side, align the groove with the back edge of the end plate and then lower it down to clear the metal fuel pipe which extends through the cover. As I lowered it, I had to look underneath the cover to make sure it was starting in the groove.


If I had a service center do this, it would have been very expensive. Simply dropping the unit is labor intensive, but not that difficult to do by a hands-on owner. Once removed, it can be diagnosed by a confident hands-on owner or brought to a service center to be diagnosed and repaired.

Luckily, I did not have to take apart my engine or generator section. Once I had the parts list and read over the service manual several times, I felt comfortable performing these tasks. Basically, I took care of rust, replaced the muffler, installed new hardware and vibration mounts and replaced wear parts such as the starter relay/solenoid and fuel pump. I then gave the unit a tune-up with a new spark plug, fuel filter, fuel line and air filter. I adjusted the screws so it was running smoothly and checked the output for the correct Hz and voltage values under load and no-load conditions. Hopefully, it will be good for many more years.
Attached Images
File Type: jpg IMG_4608.jpg (364.6 KB, 24 views)
File Type: jpg rubber mounts.jpg (437.8 KB, 19 views)
File Type: jpg Adjustment screws.jpg (105.3 KB, 16 views)
File Type: jpg generator.jpg (251.0 KB, 25 views)

jmai is offline   Reply With Quote
Old 11-29-2018, 04:12 PM   #2
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Nice writeup. Thanks for sharing.

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Old 11-29-2018, 09:15 PM   #3
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Send a message via Yahoo to bobojay

Good job!

Just had a guy in the Facebook Travato group mention and write up his having to replace the motor mounts as they had basically collapsed after 600+ hours in 3 years which was caused by replacing the exhaust pipe hanger earlier with a rigid one vs one that allows side to side and front to back movement (according to the Cummins service center).
It was an expensive job....
Bob & Sharon
2019 Winnebago Travato K (2018 Chassis)

Past RV's: 2013 WGO ERA 70A, Chevy PW Lexor
Itasca Navion, 29' Jayco 5th Wheel
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Old 11-30-2018, 01:34 PM   #4
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Originally Posted by bobojay View Post
Good job!

Just had a guy in the Facebook Travato group mention and write up his having to replace the motor mounts as they had basically collapsed after 600+ hours in 3 years which was caused by replacing the exhaust pipe hanger earlier with a rigid one vs one that allows side to side and front to back movement (according to the Cummins service center).
It was an expensive job....
It's imperative that you replace your exhaust pipe hanger with a flexible mounting. The original Onan one (Cummins Onan 1552174 Exhaust Hanger) with the rubber-like connection is not expensive. The exhaust pipe assembly, which is firmly attached to the muffler, needs to be able to vibrate. That is why this exhaust pipe hanger with the rubber-like connector is necessary. If you don't allow vibration, the exhaust pipe connection at the muffler will surely break off. And replacing the muffler involves dropping the generator, taking off the top cover and replacing the muffler which is currently close to $150.00

Regarding the motor mounts, (Onan refers to these as vibration isolators) which are essentially a wear item. They are made of rubber and are situated between the mounting pan and engine. This location generates a lot of heat and can get coated with oil if you have a leak or seepage. Both of those conditions will deteriorate the rubber over time. The engine needs to be mounted so it can move. If you actually watch the generator when it starts and then runs as it warms up, it moves and shakes quite a bit until it settles into a constant RPM. So, if your unit has many hours or is fairly old, it certainly is beneficial to replace them. Again, fairly expensive, currently $26 for my Onan 2.8 KV. Better to replace them "while you are in there".
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