1 gallon of gasoline is equivalent in energy content to a lead acid battery
weighing a mere........2144 pounds.
Brent Covey
[HEAD REMOVAL] [MUFFLERS] [ONAN VIDEOS] [Weight] [Other generators] [Dual Fuel]
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 How do I get 220 volts out of my Onan?

"I (actually my chief engineer) split the two coils to provide separate 110 to two separate circuits. Two 110 hots and a ground give you 220 if needed. In the installation manual for BGE, NHE Gensets Manual #965-0628 of 2-92 page 7-4 the schematic #611-1206 for 60HZ generator.

He moved:
T4 From L0 to L2
T3 From L1 to L0
CB2 From L1 to L2
This is a totally unauthorized switch and what you do is up to you. (Marcus McGee)
The onan wasn't rewound, it was re-connected, from paralel to series or the
other way around.  The compound reactor was replaced by an electronic
regulator. I'm still trying to find the exact schematics. When I have them I
will tell you all. Marc Hogenboom
Dual Fuel / Propane  Onan Conversion

Here is a Propane conversion

And a dual fuel conversion
I posted some pictures of my dual-fuel Onan conversion:

After replacing the Onan with a Genrac in the GMC I did not have the heart to scrap it. So it sat around for a while until I decided to make use of it. So I mounted it to a cart, fixed all of the various problems it had and set it up for dual fuel operation. So now I have it as an emergency backup generator. I have used it from my home LP gas supply and from 20lb gas grill cylinders. I have not had problems with them freezing but I have not used them in cool weather either.

it is a good idea to re-gap the plugs to .018" if you are primarily running on Propane or natural gas. It is easier on the ignition system (lower peak secondary voltage) and still runs OK on gasoline.
I have not attempted to see what happens at full load. I suspect the output will be less when running on propane because the raw gas takes up more space in the combustion chamber. So, unless you increase the compression (so as to take advantage of the higher octane rating of propane) the horsepower will go down when running on propane.
With regard to gas tank icing there are a number of issues. First I only tested it on a 20Lb tank  while powering a 15K BTU A/C, refrigerator and some lights. So I am not sure what will happen under full load.
The other problem is knowing what is in your propane gas tank. The mix of propane/butane etc. (and thus the vapor pressure at any given temperature) found in cooking gas varies from region to region. But I suspect that placing my 20Lb gas tank near the hot air outlet of the Onan would probably be good enough to keep my gas flowing in a pinch.

I am not sure what will happen if you try to run the Onan from the vapor outlet of the existing GMC propane tank. Maybe someone else who has tried this can chime in. The propane heater is rated at 35K btu's input/hr and the propane hot water heater uses 5K btu's input per hour. I dont think there is a problem running them both in cold weather from the onboard propane tank.

I am not sure how much gas the Onan takes while running. One HP is about 2550 BTU's/Hr. So if the Onan takes the same gas flow as the heater/water heater then that would be something like 15Hp fuel input (about 11.5Kw). Not sure what the efficiency of the Onan is. But if we knew, that could be a starting point for guessing how much load you could expect to carry from the on-board propane tank.

I used a Garretson model KN regulator:

These are cheap and very common. Any place that services standby generators or fork-lifts will probably have them or be able to order one for you. You must also order a 12v gas valve. Do not attempt this conversion without installing an electric gas shut-off valve connected to the fuel pump circuit. You must have the gas turn off automatically whenever the generator quits running (for safety reasons).
These guys also sell conversion kits for various engines. I am not sure if they have one for the Onan.

I mostly use the Onan connected to my home propane supply. I am using flexible 3/4" (maybe 5/8" ?) gas line connected to a shut-off valve on a 'T' at the output of the secondary regulator (the one on the side of the house). The few times I have used a portable tank I used a regulator on the tank with a short gas line connected from the output of the regulator to the input of the gas valve. The regulator from a gas grill is too small. Use the larger regulator that is typically used on trailers and motorhomes (like the OEM one on the GMC).

Usually when I need to use the Onan off-site I just drop the intake hose (that goes into the gas pump) into a gas can and run it on gasoline. Much easier than messing with small propane tanks. I do not remember the longest I ran it on a 20lb tank. I think it was a couple of hours but I doubt the tank was full when I started. I tried it mostly out of curiosity. Dave


No gas. Just fire it up. That's why I duel fuel the Onan. 30 minute run really cleans that carbon out of everything. Makes for sure and quick starting instead of grinding and waiting on the gas. Then flip the switch to off, when it stumbles, flip to gas. It's already there! Conversion is simple. You just cut and fit the mixer in the flex filter intake. Take only 2 to 3 inches of hose out of the length. Heated regulator, couple of solenoids, double pole double throw switch, and a line to your old freeze-em off tank. You know.

You can stuff a hose into your GMC carb and run it off lp. Just crank it up, cut off the fuel, stuff the hose and when it stumbles, start feeding the lp. Not too fast or it will flood. Too slow, no go. You can't touch the accelerator unless your good with your thumbs and can get used to being a carburetor. I got good at it and field test run possible old beater engines this way all the time.

Beats a can of gas, old gooey carbs, fuel pumps that won't work, etc. Just take a vise grip on an old beater, pinch off the fuel line so it can't get whatever might be in the tank, make sure you got ignition and fire her up! So many iffy's are instantly eliminated. -Eddie- Houston, TX

Head  replacement and decarbonize
Here are pictures and information

Other Generators installed in the GMC
    23 foot - generac -Gary and Joanne Worobec

Denny's - Inverter Generac

    26 foot GMC

GENERAC- Heinz,%201999%20-%20Project%20completed



Generac Prime pac 50 g
GMC mounting by Miguel Mendez

Honda EV6010 3/24/05

6KW power drawer Onan Weights 405 Pounds

I can' speak for any other 6KW Power Drawer, but the one I weighed was 382 # + 16# for the bracket + 7 # for the muffler, making  a total of 405 pounds.  I used 2 bathroom scales and weighed several times averaging out the small differences of each weighing, so 405 pounds should be PDC.  P. S. the oil was on the full mark with the fuel bowl empty, the elevation here is 48 feet and it's PD hot today.

Marsh Wilkes

Due to a request, the replacement motor mounts for the Onan Genset is available from "M & D Mower" on the web. The correct part number is "ONA-402-0284". Current price is about $20.00 and you need four.
To check if your motor mounts have collapsed, just put your finger in the hole in the center of the Onan cover, if you feel a bolt head, your mounts are good, if you don't, your mounts are bad. Be sure that your finger is parallel to the ground, without any bend in it. Tom P

How to install  by Arch


Well at least I know you have your copy of Mr. Onan's video "Onan Troubleshooting & Maintenance".
What? You don't?  You must not have gone to the Palm Desert Spring Rally. We gave one free to every attendee.   You really need to go to these rallies.

But have no fear, the video is available and you can order one for $12.

Contact Toby Maki at:

You will be amazed at how much you get from watching Duane doing the preventative maintenance live on video.  He has so many hints during the presentation that are just not covered in the printed version.  This is good fun.


This is an item known to fail with catastrophic results.  Check yours today
her interior and parts of her exterior were cremated as a result of metal fatigue & failure of the Genset muffler support bracket, this failure, allowed the muffler to put excess stress on the exhaust pipe, resulting in its cracking , releasing hot exhaust gases to impinge on the fire wall of the generator compartment, unnoticed, because of road noise & traffic , the excess heat on the metal firewall, overheated the wooden walls on the inner portion of the bedroom of the coach. It appears that the genset fuel line or filter let go as well, judging by the chimney effect on the left rear coach corner post above the gen compartment. ( along with the wind from road speed) John
My 74' has the same burn mark on the generator compartment. All I found was a thin piece of sheet metal screwed to the underside of the compartment. Didn't do a whole lot of good. The exhaust manifold's   heat went right through, and burnt the wood nicely!

What I plan on doing, is to use a heat shield material called FiberFrax, and line the compartment with it.. It is a ceramic material rated for 2200* . Neat stuff, took a piece of it and while holding it in my hand, took a propane torch to it. Never felt any heat through the stuff. Of course I have the advantage in that I am replacing the compartment and am planning on raising the height about 1 inch.

Oh, you can get FibreFrax from Aircraft Spruce:
Electric choke
I had the same problem in 1988.Took the electric choke apart,problem was the metal part that moved was rusted to pieces.The case and electric magnet was fine.Bimetal spring was shot also. Enough of the internal part was intact to make a duplicate from a 22 gauge piece of galvanized tin.
The new part was crude but it worked.The electric wire supplies the electromagnet,which pulles flap and the choke rod while cranking the engine.A bimetal spring inside controlls the gradual controll as heat rises.

Think the bimetal spring was eliminated and now the choke goes completely open after start button is released.The home made piece has worked very good for last 14 years.

The valiant choke may provide internal parts that can be used to hand remanufacture the Onan electric choke ?  Lawrence Gaskins

this was posted by Jr.

If you look at this GMCPhoto site you will see a drawing of a bracket that supports a replacement for the Onan Choke.
Here is the web site.
Bruce Tara

15000 meter is perfect replacement for the old hour meter.

Is there a cheaper fuel pump for my Onan?
Here is a current pump
by rob

Part number 73EK9147B, page 23, catalog 62F priced at $34.99
This is a Facet pump, 2-4 PSI output. The picture is identical to the John Deere fuel pump (for a 105 (gas) combine) I bought for about $45 or so earlier this year, which is identical to the pump that I didn't buy at Onan of Indiana for $93 and change. (Mark Grady)

5 years ago before I knew about the Jims, I replaced my onan 6kw fuel pump with this identical pump Maximum pressure 1.25-1.75 psi haven't had a problem since and was exact replacement taking only 5 minutes to swap out. Not sure what others are selling as no picture, the price has risen substantially as I think I paid something like $65 back then. (4.9.10)  John Blankenship

Onan / Propane Door Lifts

I was uncomfortable with the doors hitting the lifting cylinder brackets  in the original article

So in true GMC tradition, I changed the bottom brackets on mine.

Part numbers from

Ball mounting , 90 deg angle inverted ball bracket              9512k95
Ball mounting, 10 mm ball stud w/5/16-18 male thread      9512k73


23 ft GMC Door Lifts (230 by KenH

When I bought some door lifts from Gasco in Florida about 10 years ago, they came with some directions on how to reinforce the door so the hinges did not crack the doors due to the increased loading from the air lifts.  Their directions were to drill out the pop rivets for the hinges and fill the cavity adjacent to where the rivets were attached with Bondo (I used the fiberglass filled Bondo).
 Then, drill through the original holes for the hinges, through the Bondo and through the second fiberglass webs just below where the hinges were attached.  The hinges were then reattached using # 10 bolts.  By filling the cavity between the two door webs, the hinge mounting is probably more
than three times stronger then the original configuration. Chuck

Governor Adjustments and more bad connections

On the trip to Palm Desert, my Onan was not putting out much voltage when a load was applied. When I had the water heater and the coffee pot going at the same time (under 3000 watts) the voltage would drop to about 100v. I tried adjusting the carb, the governor speed and sensitivity and got the voltage to finally hold at 110v with this load. However, I didn't go back and check the no load voltage. Unfortunately, I later discovered that my no load voltage was in excess of 150 volts (thats as high as my plug in voltmeter would display) and the result was that I fried my Statpower charger when I started up the Onan the next morning.

The manual shows that if a high low voltage occurs when there is no load at 1800 rpm but the loaded condition has the proper voltage it is probably a bad "compounding reactor". So, I started working on the Onan with this as the premise. I quickly discovered that I would have to remove the whole brush end of the Onan to get at this part so I decided to see if I could test it while in place.
It has a lead going to the bridge rectifier which is easy to get at by just pulling off the plastic cover under the lower rear part of the brush housing. While under the Onan I accidentally discovered that another lead going to the rectifier was very loose at a connection and would not hold together. There are two male/female spade connectors going from the field windings to the + and - terminals of the rectifier. Each set is in its own approximately 2" plastic insulating tube. They are made of brass and I found that there was very poor contact as the brass female connector had lost its tension. I attempted to squeeze it with some needle nose pliers and it immediately cracked. I then soldered in a new steel female connector, coated it with dielectric grease and plugged in back to the male connector in the tube. I checked the other connector and found that it also was making very poor connection and was also loose in the tube. I replaced that connector as well.

I next started the Onan and found that I had much higher voltage than before. I used a mechanical tach through the front flywheel cover hole and set the no load to 1800 rpm which corresponds exactly to 126 volts. I went through the various adjustments with the carb, the governor speed and the sensitivity and was able to get 126 volts at no load but it would still drop to about 110 with 3000 watts. That's about where is used to be and I figured that I would have to live with that and just turn the water heater off when I wanted to use the microwave as we had been doing for the last few years. I then noticed the paragraph in the maintenance manual about the linkage adjustment (from the carb throttle to the ball on the governor arm). I had never adjusted that so I decided to check it. Following the instructions, with the Onan off, I popped it off the ball joint and held the carb wide open against its stop and checked the end against the ball joint. I found the linkage to be about 1/4" too long. I rotated the end until it just fit over the ball stud. I then restarted the Onan and readjusted the carb and governor until I again had 126 volts at no load. I then started to turn on electrical equipment and found that the voltage never dropped below 120 volts. I started with the water heater, added the coffee pot, the air conditioner heat strip and even the microwave and it would still hold at 120 volts. I calculate that I had about a full load of 6000 watts on the Onan. It has never done this before in the 20+ years that I've had the GMC.

I had never thought to adjust the linkage arm before. In fact, the factory paint was still on the threads when I turned the end to shorten it. It apparently had never been set properly by the factory.
I also noticed that there are two more of the connectors in the same type sleeves on the left top of the Onan in the wires going to the fuel pump and to the solenoid. I checked these but they were tight. Apparently the heat from the engine and generator caused the lower brass field wire connectors to loose their temper and thus cause a loose connection.
I would suggest that everyone check these two connectors and the carb linkage on their Onan. There was nothing wrong with the compounding reactor. I believe that my initial problem was occurring because of intermittent contact on the field windings.
Emery Stora

Generator / Propane Door Lifts

Onan Carburetor

Although Onan carburetors are no longer available the company that made
them can factory rebuild them and offer parts. The contact is:  Luis
Salis, Walbro Corp., Carburetor Div., 6242 Garfield, Cass City Michigan
48726 and they can be reached at 989-8722-2131.

I talked to Luis Salis this morning; and he confirmed that is company will still rebuild the old Onan carburetors.
     (a) The carburetor should be sent along with a check for $45 to the company address, attention Luis Salis.
     (b) The check should be made to: Walbro Engine Management / Luis Salis
Robert Musgrove

My friendly, but expensive, Onan repair depot found a dealer that supplies a rebuild kit for Onan 6500 NH carburetors.

Source: V.E. Petersen Co.
Phone: 800-537-6212
Kit Number: K1LMB
Cost: $7.85

Onan carb float bowl gasket no longer available by GM number or Onan --
Briggs & Stratton 281165S.
(This is a unique square crossection round gasket that fits into a narrow groove in the carb). This one
was a dead ringer for my 6 KW.Sorry I don't know who provided this # Marlene

4K Onan circuit Breakers
Your friend probably has an Emerald Plus model which has two circuits and two
circuit breakers located on the back of the generator. One circuit is a
heavier circuit than the other. Reset both by reaching to the back and
pressing on the breaker buttons. The load each will sustain depends on how it
was wired in when  installed. I have a 6.5 Emerald Plus and that's the way
mine is. If I run the rear A/C and the water heater comes on, it pops the
circuit, but I can run the front A/C and anything else in the coach with no
problem. Hope this is the answer.Andy M,

Circuit Breaker keeps popping
Onan selected a very marginal CB design for some of the Onans.  The type with a reset button is JUNK.  If that is what you have, replace with an industrial grade CB that will serve you well.  Even if you have the standard toggle type, now may be time to replace it also.  Find an Electric supply shop & request a "Quick Lug" type CB & adapt it into your OEM Onan CB box.  The "Quick Lug" type CB has a lug for input & a lug for output.  Cost about $10 & will outlive the coach.  For a 4 KW use a 40 amp CB,  For 6 KW, use a 50 amp CB for Onan protection. Duane

Wakening a Sleeping Giant (Onan)
For an Onan that has set for several years w/o operation, I would do the
following after changing the Oil, Oil Filter & Air Filter: NOTE: DISABLE

1)  Remove the cover over the control board & spray all board & wire terminals with an Electrical Cleaner (2-26 at home center, electrical dept.).  Spray all Onan wire terminals in sight. Wait for cleaner to work, about 1 hour (WD 40 can be used, but not as good.

2)  Remove carburetor to Fuel pump hose.  File off brass crimp sleeve & find barb fitting.  Replace w/fuel hose (3/16" I Think).

3)  Remove Carburetor & clean (Existing gaskets should be OK to reuse).

4)  Clean all Onan Battery cables, both ends.

5)  Now that the cleaner has had time to work, it is time to evaluate if  you fuel system is functional.  Jumper board terminal 9 to 5 & you should hear fuel pump & see fuel coming from pump.  Got to achieve this step before anything else (Need Fuel to function).

6)  For test purpose, remove the following wires from the Control Board:  All wires on upper board terminals & terminal 12.

7)  Reassemble fuel line & carburetor & jumper board terminal 9 to 5 & let pump operate for a few seconds.  Hit the start button & she should run.

8)  Adjust carburetor Hi speed jet (lower side of bowl) for smooth running.  Monitor the Onan output voltage & adjust the Governor shaft nut for 125 to 125 V AC w/o load.

Now you should be ready to connect Onan Power to coach for evaluation under load.

Onan Runs with Jumper in place.  My advice is to use terminals 9 to 5 for jumper (not 9 to 11 as book states).  9 to 5 provides a 5 amp fuse protection that 9 to 11 does not. First: comments on No AC Output:  Lanier's statements is what I would do to determine if the Circuit Breaker is faulty,  then remove (CAREFULLY note the Bridge rectifier to connector base orientation...mark with tape/paint...both items).  The connector base & BR should have marks for inserting the BR (+ on connector goes to + on BR).  Via the marks added, verify that the BR was installed properly prior to your removal.  The BR can be installed 4 different ways (not mechanically keyed) & only one way will function & one way will zap the BR.  The BR can be evaluated/tested
with an ohm meter/diode tester function per GMC Manual instructions.  If you have a bad (verified bad BR) then it is time to replace with an aftermarket High Voltage BR.  The connector base has to be altered to accept an aftermarket BR, but it is well worth it.  Instructions latter
for this if needed.  If CB or BR does not fix problem, then look at condition of the Brushes & associated wires.   GOOD LUCK on AC fix.

Now the Control Circuit (could be the board, but don't jump to early conclusion):  Need to make some measurements & wire removal first.  What ever you do, don't, again I say don't get hooked into an aftermarket Onan Control documentation on board & therefore no existing trouble shooting information...also an Onan shop will not work on your Onan until the board is replaced with Genuine Board.  Also it is cost effective for me to restore/repair the OEM Board.

General Trouble Shooting:
1)  Spray the Board terminals with 2-26 Electrical Cleaner (Home center) & let it soak in.

2)  Remove the wires on the board's upper terminals & terminal 12 (not needed for operation with board stop/start switch)

3)  Try to start Onan.  If No start, the n monitor DC voltage between terminal 10 & 1 and 11 to 1 while cranking Onan starter.  Must have a minimum of 10.5 V dc (should be more like 11.5 or 12 V).  If not, then charge Battery & clean all Onan Battery cables (Both ends of all cables).
 Must have 10.5 v dc minimum to proceed.

4)  Now probe board fuse & verify 12 v dc is present at both ends of fuse holder.

5) Jumper terminal 9 to 5 & you should hear the fuel pump running.  Hit Start button & Onan should run.  Note you have been there done that.....OK do it again.

6) measure the ac Voltage present between terminals 8 to 11 as information only.  Should be 28 to 30 V AC.

7)  Stop the Onan & remove the wires from the Voltage regulator & CAREFULLY  tape up the single wire alone.  Remove the other wire or wires & tape them up while maintaining connection of the two wires if so configured (some Onans have only two single wires attached to VR).

8) Now try to start Onan w/o jumper.  If it still want start then it is time to remove the wires from the board & mail the board only for Board Test & repair as necessary:  Place in small CARD BOARD BOX (no paper sack with bubble wrap) to following:
Self insure to prevent days of delays at my post Office since they  will require receiver signature ( most time mail comes I am not at home & it gets sent to main post office for pick up...the other side of town & 2 to 3 days delay before available)  Self insure,  have not lost one yet & I have back up board if needed.

PS:  After Onan is functional w/o jumper, replace wire to terminal 12 & verify operation.
Then replace upper terminal wires & verify operation.  HAPPY ONANING !!!

Hope this helps you get started on Onan restoration
Duane Simmons

Spark plugs - I'm running Champion 844-1 replacement for H10C. lanier

Order  Onan Parts
The Denver-area dealer, Cummins Rocky Mt., will ship parts UPS.
Or you can call Onan (800-888-6626) and they will put you in touch with a
dealer closer to you if you are not in this area.Richard

Alex Sirum GMC has lots and lots of old Onan's cluttering up their
warehouse, give them a call.  Phone 863-763-1121  e-mail Jim


The $65 Onan muffler and down pipe

See the complete story at

Did it, tested, works for me, looks good too.

Muffler Napa Part number: 22769, $49.55
Napa Elbow: 41000, $5.86
Pipe from Aarow: $10 cash
Clamps: $3.00 Mike Teets

After a lot of searching I could not find a shop that could do or have  the one and one quarter inch tubing for the Onan exhaust. One shop told me that he used 1.25 galvanized conduit from an electrical supply. That is what I used.  Heated it with a torch and bent into the shape I needed.  Note. heated galvanized puts off a poisonous gas.  Use proper precautions Monte

Onan Stainless Muffler
 GOLBY's muffler kit. Called Golby and they sell
the stainless muffler and exhaust tube for $156.00.manny


There is a retrofit point set up that has a cap that comes off the top to access the points and also has an allen wrench adjuster screw for the points.  The complete kit goes for a little over $100, used to be less but you can thank Onan for bumping the cost.  It is easy to install and man is it easy to adjust.  The part # is 160-1303.  I can get them for @ $120. Bounds

[pertronic] [Onan]

I got the directions on how to do it from Ken Henderson's and Lawrence Gaskins' previous postings here.
The postings are long so please go back and look at the following:

1. Ken Burton - Onan Ignition Timing - posted on 8-28-03 at 4:48

2. Here is Ken Henderson's posting to the GMCphoto site:

3. Here is Lawrence's write up with pictures:

I followed Ken's example except I mounted the pickup further clockwise around the flywheel and added an extra ground wire.  I also set my timing at
25 degrees BTDC.  If you read my posting you will see why I chose that setting.  If you do not like my reasoning then use whatever is marked on the
flywheel. ken Burton

4 Here is Rob's  pertronic install

Onan Electronic Ignition by Chuck Aulgur
Before you start this project, be sure to read the article above to determine if you need a new baseplate for your Onan.  The early models need this extra part.  I feel the Onan should be running before your start this project.  Also set the timing as talked about below, so that after you install the electronic igniton, you will know the Onan worked  at this timing before. gene

Onan Electronic Ignition by Emery Stora
photos by Mr.C
The Onan electronic ignition system can be made to fit all Onan  twin-cylinder engines and generator sets built since 1973 with top adjust  points.  This includes all (Model NH) Onan generators installed on GMCs.   It  is called Magna Arc, part number 160-1376. I believe this is the only one  they have called Magna Arc.  It contains an ignition module, cover and cover  clip, base plate and gasket.  It sells for approximately $120 .

Click for DetailThis new unit will not fit as is comes out of the package. The main problem with the new unit is there is insufficient room to make adjustments to the adjusting screw, so you can cut off both right angle sheet metal bends that hold the adjusting screw and discard the adjusting screw, spring and washers.  It is very easy to do this with one cut.

Hold the unit with the black block toward you and the adjusting screw to your right.  Loosen the adjustment hold down screw and move the two metal bracket pieces so that they are lined up even on the left side.  This will give you enough adjustment slot to time the engine.

Remove the adjusting screw, spring and washers and make a cut with a hacksaw on the right side just even with the outside of the hold down washer.  Throw away the two small pieces you cut off.  File the cut edges smooth.

Then remove the points and condenser from the old base plate and remount the new parts to the old base plate, using the new base gasket.  The new components will screw down under the two screws used to hold the base plate. You will  need to file a few thousands off the inboard side of the threaded post protruding up from the base plate to provide clearance to mount the assembly.  If you do not do this, the push rod pin will jam in the bracket and not go up and down.

Then time the engine using a timing light per the instruction sheet. Disregard a lot of the timing instructions that come with the new kit.  They talk about marking the shaft and even removing the cover.  You don't have to do that with our Onans.

We have a small hole, about 1/2" in dia. on the top inside of the fan housing for timing marks.  Start the engine  by holding the two parts of the assembly roughly even and moving them slightly to get the engine running smoothly.  If the engine will not start, make sure the white magnet bar is moving back and forth when you are cranking the engine.  The push rod might be jammed as described above.

Point your timing light at the hole and there will be a single timing mark.  Your timing light can hook up to either of the plugs. Both fire at the same time.  Move the bracket by finger adjustment until the timing mark lines up in the hole.  Then tighten the locknut on the adjusting back plate when the timing is correct.

The new cover has a grommet that fits over the wires.  If you drill a hole in the new cover in the same location as the old cover screw hole on the top it will fit and you can discard the new cover clip.

Click for DetailThere are two wires coming out of the module. The red one goes on the hot (+) lead to the coil (the back one on mine).  The black lead goes to the ground (-) side of the coil. The old points had a push on connector.  The new black lead has a ring connector so it will be necessary to get a nut that fits the threaded terminal.  The Onan is much easier to start and performs exceptionally well.

Emery Stora
It is really not necessary to set the Onan frequency.  The output voltage and the frequency are linked inside the Onan and they are not adjustable seperately.   If you set the unloaded output voltage  to 125 to 128 volts the frequency will be correct.  If you want to check the frequency, the following is a neat trick. gene
To adjust the frequency (speed) of the Onan you need a 120v ac/dc neon test light .. available at Home Depot, Lowes, etc. Be sure to obtain a 120v light, some are rated for lower voltages.

A simple setup is to power the coach from the Onan & have an extension cord plugged into a commercial  power outlet. Put one probe from the test light into one of the Onan outlet slots (NOT

the round ground pin). Put the other probe into one of the commercial power outlet slots. If the light glows continuously, remove one of the probes & place it into the adjoining slot of the Onan or commercial outlet. Do NOT switch both probes. The light should pulsate when properly hooked up.

When the Onan frequency (speed) approaches 60 hz, the pulsation will slow until the Onan freq is exactly 60 hz at which time the light will extinguish. That is not likely to happen, as the Onan cannot maintain exactly 60 hz. Therefore, aim for the slowest pulsation. With my Onan, and I assume most, 60 hz produces exactly 120v. Obviously, the higher the freq the higher the voltage, and vice versa.
Edgar Kremer

Onan Oil Pressure Switch-testing/replace

The GMC Onan oil pressure switch must be a "Normally Closed" type to function properly with the control board.  Take the original Pressure switch to you local Auto parts store & they can match it with the proper switch arrangement (contact closed w/o pressure... measure it at the counter).
 The Onan Control Board does provide a shut down function when the Onan is Low on Oil (Oil Pressure) call "Low Oil Pressure" (LOP) function.  However, one never knows if this function is functional unless a simple test is accomplished or you "Smoke" your Onan engine.  Best to
periodically test this function as follows:
With Onan running, jumper terminal 12 to 1 & the engine should start to stop in 2 to 5 seconds if the control board is functional.  If it does not start to stop in the prescribed time or immediately, it is time forboard repair or don't depend upon this function.  Best to repair !!!
Cost effective board repair (OEM ONAN Boards only) is available from me as required.
Also, conduct the following test to verify that the Oil Pressure switch is functional:

Remove the wire from Board terminal 12 & probe the wire end to chassis ground & it should be less than 1 to 2 ohms.  Now start the Onan & the wire to chassis ground resistance should open with oil pressure (near infinity reading).  If this condition is not verified, disconnect the
wire at the Pressure Switch & verify that the wire is not shorted to chassis ground. If wire is not grounded, it is time to remove the Pressure Switch & a trip to local Auto Parts store to get replacement (Common part with many auto application).  Happy Onaning Duane Simmons

Here is an after market part number for your Onan oil pressure switch:  I just installed one and it works fine:  NAPA # OP6074.  It replaces OE on several 80 ish GM vehicles and a 90 ish Geo.  Normally closed.  Opens 3 - 8 psi.(don't have specs on Onan OE).  Has the correct thread.  A funny British thread which looks like metric.Hope this helps.byron maxwell
I found some misinformation posted by Byron Maxwell .
He days a NAPA OP6074 will work and then says it has a "funny British thread that looks metric". The problem is that the Onan takes a standard pipe thread,
1/8 - 27 tpi tapered.
The part number from Byron has a straight thread, not tapered.  It  would thread in but don't what would happen when it hits the taper. Emery

NAPA # OP6282 = Borg Warner # S310
                Light Type 3 - 8.3 psi
                1/8 x 27 NPT
                Chrysler 62 - 78 & 82 - 85
                Jeep 55 - 59
                Numerous other Chrysler products circa 70s - 80s
Onan Oil Filter Replacemets
Any of the following filters will fit the onan.  They may not , however have the built-in bypass that is needed for cold weather user.  This bypass allows oil to the engine when the oil is too thick to go through the filter.  The Onan filter cost $7 which is  not too bad.  gene

Fram PH-28A of PH2870, Hasting 134, Lee LP-2131, Mopar -323, Motorcraft FL-271, Purolator FCO-252 .
I use the AutoZone Deutsch D484 and Most are under $4.  The Onan filter will cost you.J.R. Wright

I contacted Bosch Co. Technical Service to verify the prior post that Bosch filter #3421 contains a by pass valve (desired for Onan application since there is none in the Onan Block).  Bosch did indeed confirm the prior report that #3421 does contain a bypass valve in the filter.  The bypass valve may be viewed by looking into the center hole of the filter. The spring mechanism located in the center tube below the threaded back plate is the bypass valve. Just Though You would like to Know Thanks for the prior post Duane
You may be interested to know that according to the local AutoZone, the Deutsch
line of filters they carry has been bought out by STP.  The Deutsch D484 filter
for the Onan is S2870A in the STP line.paul

Onan Runs But No AC (110)

Testing for Flywheel Alternator Voltage
You can see if the Control Board is receiving the Flywheel Alternator voltage by measuring the AC voltage between Terminals 8 & 11 while the Onan is running.  The AC voltage should be between 28 & 31 volts AC.  When the Voltage Regulator fails, it can load down this signal to less than 20 volts AC & the control Board will not function.  OBTW the Voltage Regulator is not needed for operation of the Onan today.

 The Onan failure that you have describe is a classic "Bridge Rectifier" (BR) failure.  However, they typically fail while turning off the Onan while the AC is running.  A voltage transient is generally the cause of failure due to the fact that the OEM Bridge rectifiers are operating very near to the Peak Inverse Voltage (PIV) rating of the OEM Bridge rectifier.

A simple solution is to replace the OEM BR with one of much higher rating.  However, I have not been able to find any  aftermarket BR w/the same pin-outs. A simple modification to the base (holding device) is capable to accept the four wires as feed thru(directly attached to  the terminals of the BR).  A 1/4" hole in the base for each wire is all that is required. To remove the BR, side out the Onan as far as you can & remove the BR mounting screw which is located aft of the Control Board on the rear Generator Housing (1/4" screw head).  Remove the plastic cover on the side of the generator housing & the BR can be moved to where you can ID the terminal from the side of the BR.  Carefully...Carefully....Carefully transfer the terminal ID to each wire (ie.  + , - , AC , AC). Transferring the proper ID is very important since the Onan will not operate with crossed wires & the wires are very hard to trace for ID. Now individually remove the wires from the base (relive tab on each wire terminal from the front/BR engagement  side & push terminals out the rear).  Now  drill 1/4" holes for each wire.  Slide the wires thru the proper hold & attach/slide on the 4 wires to the BR.  Slide the BR & wire terminals back down thru the base to where the Original mounting screw will secure the BR to it's original position on the housing. An after market BR w/1,000 volt (PIV) rating is available from many Electronics stores at less than $10.  The PIV is greater than 3 times the OEM BR & should never fail (well almost never).  NTE # 5328 is the after market BR that I use.Duane

Onan Bridge Rectifier Replacement--

Aftermarket. NTE is an Electronic Packing House that distribute thru-out the US at many Electronics Stores (not at Radio Shack).  They have a Bridge Rectifier P/N NTE5328 which works great in our Onan, except the Pin Out is different & requires removal of the oem plastic mount & individual insertion of the connecting wires. Care must be taken to get each wire in it's proper place & then attach the Bridge Rectifier with it's original mounting screw.  The Electrical characteristics of this aftermarket Bridge Rectifier is far superior to the OEM (1,000v PRV & 25 amps).  This device should never fail (well almost never) in our Onan application.
"Note:  Drill 4 each holes into the original plastic mount such that the individual attached wires have clearance in the  mount for installation  with the original mounting hardware."
As I mentioned about a week ago, I fried the original bridge rectifier on my Onan. I'm aware of the connector mod to allow more readily available rectifiers to be used, but I didn't feel like fooling with the connector, and when it's 103 outside, you have to make these jobs as quick as possible. After looking around, I thought I found a higher capacity rectifier (KBPC3510)with the correct pin outs, but alas that was too good to be true--their picture was incorrect. However, when I recieved them (I bought 5 of them for $2.50 each) I noticed that the pins were necked down as they enter the potting material such that they are easily twisted to the needed configuration. They have a rating of 35 amps at 1000 PIV--much more than the originals. It worked like a champ and made the change a 5 minute job. I also notice that when I start the Onan, it comes up to voltage almost immediately where it used to take a couple of seconds--no big deal, but a change. So far so good, and I now carry a spare which I'll probably never need. Bob de Kruyff 5/18/06

Pictures or the bridge

 From the FAQ at:
How do I install a new bridge rectifier on my Onan?
To replace the Onan OEM Bridge Rectifier is a 10 minute job. Takes a little longer to install an after market High Voltage Rated unit since the pin out arrangement is different, but it is worth the effort for piece of mind. Slide the Onan out as far as it will go & go to the right rear (behind the control Board) & remove the two black plastic screens around the Generator
Housing. Between the two screens is a 1/4" bolt head on the generators housing. Remove this bolt & the BR will drop down out of the housing. Carefully note the pin out orientation before removing the BR. The BR will insert 4 different ways.....only one way don't screw up & get in a hurry. ( Simmons 6-2-00)
DON'T REMOVE THE GENERATOR!  Pull out the drawer.  Lie down  under the back side near the control board.  Reach up and you'll see  a plastic screen on the generator housing.  I believe that Gene  Fisher has pictures on his site.  There is one screen on the front  side and one on the rear side.  Take out the screw from the center of the rear one.  Pull out the plastic screen (just a couple of tabs that hold it in place and it easily pulls out).  Reach up into the  hole and you can pull down the rectifier plug and rectifier.  From that point its just pulling the rectifier and reversing everything to get it back into place. Emery Stora
Water is the worst thing to apply to you Onan.
It is not designed for bathing with water.  The maintenance manual is very clear on this subject.   Water creates corrosion on all of the Electrical contacts which deteriorate in time & become Big Time Problems in the future.  Compressed air & a rag works great when the Onan gets dirty.    Bathing the Onan is like taking the back off of your Color TV & hosing it down.  Damage is done !!!!

Onan Control Boarding Testing
 You might want to try the following to eliminate the problem:
 1)  Clean your battery cables (both ends & both + & - Posts) &
       charge  battery
 2)  Disconnect 12 pin connector & clean terminals w/cleaner &
       re-shape  female connectors to round shape
 3)  Remove wires (typ 3)  from Voltage Regulator & tape up permanently
 4)  Remove wire from board terminal 12 for temporary  test
 5)  Remove all wires from top board terminals for temporary test
 6)  If all else fails to clear the problem,  mail me all of your
       boards & I will       test them to see if they are still
       functional....minor test & mailing charge

     The items identified above are the most common failures that
      prevents the control board from functioning properly. 

"GMC OEM Onan Control Board Total Repair & Restoration
to OEM configuration & Characteristics is available from the following GMCer:
 Duane  M Simmons,  (no longer available)

Repair of your board is cost effective with customer satisfaction warrantee. Mail your board for repair & return will occur within a few days (normally...if not on long GMC trip). Installation & trouble shooting instructions are available w/repaired Board."

Air Cleaner Problems
I spent several hours troubleshooting before noticing that the air intake hose from the air cleaner to the carb was totally collapsing upon start-up...the air cleaner was clogged.

Washable/Hi Flow Air Filters are available from K&N Company
that fit our Onan Generator set as follows:
        mfg:            K&N Company
        size:           3 different heights (measure yours to place
                        4 KW Onan  has Air Filter  2" dia. & 7" Height
                        6 KW Onan  has Air Filter  3" dia. & 6" Height
        Contact         1-800-851-5334  (Direct Buy-Allison
        Cost:           Approx.  $25

 When I changed out the filter on my Onan today I noticed that the rubber hose (duct) that goes from the filter housing to the carb was split.  I had never noticed this before as it was split along the bottom side and not visible from above.  I also couldn't find the Fram replacement filter so I adapted a K&N after finding a replacement hose.  Click here:

to see 3 photos of how easy of a project this is.  I used K&N P/N RU-0810, and Gates radiator hose 20457.
  BTW, the whole project costs less than the OEM air filter from Onan/Cummings.Steve F.


After-market Onan Starter bracket is available from:
APPLIED GMC Shop email
Santa Ana CA
Cost  $49
The Starter Bracket is a highly strengthened  Iron Bracket for heavy duty use in the GMC Motorhome Onan Generator.  Have never heard of one of Ragusa's brackets  failing.  Have seen & heard of many OEM brackets failing.   I always start the Onan while pulled out of  its compartment while working on them....thousands of times.  Never had one break !!!  Never seen a correlation of Onan being in Compartment or out of compartment with regard to bracket  failing.  Could it be a coincident with not fixing the problem that caused the failure in the first place ?

"Do not start your Onan while it is extended, it will break the starter bracket"

John's Onan was doing fine until he extended it and tried to start it.  Then all H!@#$ broke loose.  Being a very observant person, he found the bracket had been broken a long time, but the starter was laying on the mounting tray (polished a nice rub spot) and as a result would still operate and start the Onan.

Ergo the myth.  Everything seems ok until you extend the Onan then the starter falls away and it is obvious the bracket is broken.  The answer is like all of these things--- good maintenance.

So tomorrow go out and tighten the bolts holding in the starter and the bracket will probably not break.  However if it is broken, go buy a new stronger one from Ragusa......

John and some others feel that the reason the brackets are breaking is that the mounting bolts holding the Onan to the rubber mounting assembly become loose  and allow the weight of the generator to rest on the starter and bracket.  Over time running the Onan and bouncing down the road, the bracket breaks.  The real answer is to check all the mounting bolts and the bolts through the rubber mounts, they are usually loose.  Sometimes one or more of the 4 rubber mounts might be missing and need to be replaced.

New rubber mounts
Thanks John Bush.

Onan Replacement Starter Information

 $205 is the cost of a new Starter,not rebuilt, at my local Onan supply.  Local shops can also rebuilt your starter at about $150.  Best buy is a new starter which has a new clutch assembly which is not included w/rebuilt unit.

The original GMC Onan starter (p/n191-1052) has been obsoleted w/o a replacement cross reference.  However, if you give Onan p/n191-1949-03 they most likely will have one in stock ($205) since it is used on several later model Onans.  Onan P/N 191-1949-03 will fit 6 & 4 KW units.  Be sure to check the mounting surface for possible interference.  A slight file or grind may be required for proper fit.  The Original starter P/N has been obsoleted & may not have a replacement noted so don't lose this number.

Also,  Patterns in Santa Ana California has a high strength steel replacement Onan Starter bracket for about $35.  This bracket will not interfere with the replacement Starter & will never break (well almost never)  About 1/3 cost at Onan..  It is a directly replacement starter that may have a slight metal boss interference with the OEM starter bracket.  A slight file job on the bracket or starter will clear this mechanical interference & function for many trouble free years.  .Duane

No Start/stop From Remote - Remote start connector problems (3/8/6)

The problem was corroded connector at rear of gen compartment. This can be seen when gen pulled all the way out on slides. Clean or replace connector. These wires go to the inside remote start and hour meter. MARK

I think you will find that the Remote Control Panel is connected to theControl Board at the top of the board on some early GMCs & does not routethese wires thru the 12 pin connector.  You will find that all GMCs have a 4 pin connector in the rear/on the floor of the Onan Compartment........the classical problem with open  remote control circuits.  Just hard wire the connection/eliminate the 4 pin connector for reliable service.  Use crimp type Butt Connectors & tape over the final wire bundle for minimizing future water contamination. Duane

Go here to see  how  to ID the connector 3/19/05 gene
In my '78 26ft model, the connector behind microwave oven on the left side of GMC was disconnected, Mike.

Onan Battery Charger /Alternator - REMOVAL
Click on pictures for larger view

Click for Detail

Absolutely no problem disconnecting the Voltage Regulator (Charger) on the Onan.
The Flywheel Alternator is the source of voltage that is used by the Voltage Regulator to provide a small output for charging an Onan dedicated (Early GMCs had small Motor Cycle type battery for starting the Onan & were charged only by the Onan Voltage Regulator).  GM quickly
recognized that House Battery could located near the Onan & serve dual purposes.  However., the Voltage regulator was never removed from the Onan (no longer required since the Dual purpose battery was charge by the Engine alternator while driving & by the AC to DC converter when shore power is available).

The Flywheel Alternator is required as a feedback signal to the Onan Control Board to identify that the Onan is running & the starter is automatically  disonnected.  Also for shut down function to remove Ignition power.  Do yourself a favor & disconnect the wires going to the Onan Voltage Regulator (Charger) for the purpose of better control on the Onan Control Board.  The AC voltage going to the Voltage Regulator is also used by the control board to tell when the Onan is running.  A faulty Voltage Regulator can & does load down the voltage to the point that the control board will not function properly for operation of the Onan.  I found this out several years ago when my Onan would not start in cold weather.  Disconnected the wires at the voltage regulator & all is well.  The AC voltage between Terminal 8 & 11 should be 30 +/- 2 volts AC.  When it drops below 26 volts you are headed for Onan Run Problems.
Click for DetailRemove the wires Click for Detail
I have repaired many Onans control problems by disconnecting the wires (typically 3 wires) going to the Voltage Regulator (faulty VR that are loading down the Flywheel Alternator output voltage).  All Onans are not wired identical, however, most have 3 wires attached to the VR.  One is by itself & 2 are common on 1 VR terminal.  After removing the wires, tape up the single wire by itself & keep the two wires together & tape them up if so configured.    (typically 2 wires together on one terminal). We should all remove the VR wires as preventative maintenance !!! Duane

Onan oil leaks
First thing to do regarding the oil leak is to take off the "S" shaped crankcase vent hose that is near the carb and check it.  I had oil coming out all over and paid for several unsuccessful attempts by Onan people to solve the problem.  Turned out this hose had collapsed INTERNALLY and was causing back pressure to build up in the crankcase.  A new hose, and no oil leaks.  May not be your problem, but check it out and hope it is because that is a quick cheap fix. Justin

If your leak looks to be just forward of the starter, the problem is likely to be the oil filter bracket.  Remove the air shield around the oil filter and you will be able to reach the two bolts that hold this bracket.  You can tighten them with a small ratchet and a long extension.  The bolts work loose over time.

Eliminate Onan K-4 Fuel Solenoid
Don't know why anyone would replace/install the Onan K-4 Solenoid.  Many Onans came w/o the Fuel Solenoid from the factory.  The ones that have a Fuel Solenoid do not gain anything due to the location Onan selected.  It could do some good if it was installed near the source of fuel not at the using end.  Why not remove solenoid & tape up the wires & be on your mary way.   While you are at the fuel line in the Onan be sure that it is of quality & not ready to break.  The solenoid will not help if the fuel line breaks & out goes a tank of gas.  I prefer a good quality Fuel Hose, not a plastic hose as the OEM.Duane

Onan Control Board Test Data by Mike