Well at least I know you have your copy of Mr. Onan's video "Onan
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
the presentation that are just not covered in the printed
This is good fun.
ONAN VIDEO FROM THE GMC DEALER TAPES
MUFFLER SUPPORT BRACKET
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:
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
remanufacture the Onan electric choke ? Lawrence Gaskins
REPLACEMENT ELECTRIC CHOKE
this was posted by Jr.
If you look at this GMCPhoto site you will see a drawing of a
that supports a replacement for the Onan Choke.
Here is the web site.
REPLACEMENT HOUR METER
15000 meter is perfect replacement for the old hour meter.
Is there a cheaper fuel pump for my Onan?
Here is a current pump
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 http://www.pegasusautoracing.
I was uncomfortable with the doors hitting the lifting cylinder
in the original article
So in true GMC tradition, I changed the bottom brackets on mine.
Part numbers from http://www.mcmastercarr.com
Ball mounting , 90 deg angle inverted ball
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
they came with some directions on how to reinforce the door so the
did not crack the doors due to the increased loading from the air
Their directions were to drill out the pop rivets for the hinges and
the cavity adjacent to where the rivets were attached with Bondo (I
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
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
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.
Generator / Propane Door Lifts
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.
Kit Number: K1LMB
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
ONAN POWER FROM ENTERING THE COACH POWER SYSTEM UNTIL VOLTAGE IS SET AT PROPER LEVEL.
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
Lanier's statements is what I would do to determine if the Circuit
is faulty, then remove (CAREFULLY note the Bridge rectifier to
base orientation...mark with tape/paint...both items). The
base & BR should have marks for inserting the BR (+ on connector
to + on BR). Via the marks added, verify that the BR was
properly prior to your removal. The BR can be installed 4
ways (not mechanically keyed) & only one way will function &
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 Board..no 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.
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
between terminal 10 & 1 and 11 to 1 while cranking Onan
Must have a minimum of 10.5 V dc (should be more like 11.5 or 12
If not, then charge Battery & clean all Onan Battery cables (Both
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
it is time to remove the wires from the board & mail the board only
for Board Test & repair as necessary: Place in small CARD
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
12 & verify operation.
Then replace upper terminal wires & verify operation. HAPPY ONANING !!!
Hope this helps you get started on Onan restoration
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
See the complete story at http://teamteets.com/gmc/onan.html
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
Onan Stainless Muffler
GOLBY's muffler kit. Called Golby and they sell
the stainless muffler and exhaust tube for $156.00.manny
ONAN POINTS KIT
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
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
around the flywheel and added an extra ground wire. I also set my
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
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
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 .
This 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.
There 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.
SETTING THE ONAN FREQUENCY
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
60 hz. Therefore, aim for the slowest pulsation. With my Onan, and I
most, 60 hz produces exactly 120v. Obviously, the higher the freq the
the voltage, and vice versa.
The GMC Onan oil pressure switch must be a "Normally Closed" type to
function properly with the control board. Take the original
switch to you local Auto parts store & they can match it with the
switch arrangement (contact closed w/o pressure... measure it at the
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
ground & it should be less than 1 to 2 ohms. Now start the
& the wire to chassis ground resistance should open with oil
(near infinity reading). If this condition is not verified,
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,
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
Bosch filter #3421 contains a by pass valve (desired for Onan
since there is none in the Onan Block). Bosch did indeed confirm
the prior report that #3421 does contain a bypass valve in the
The bypass valve may be viewed by looking into the center hole of the
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
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
However, I have not been able to find any aftermarket BR w/the
pin-outs. A simple modification to the base (holding device) is capable
to accept the four wires as feed thru(directly attached to the
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 &
the BR mounting screw which is located aft of the Control Board on the
rear Generator Housing (1/4" screw head). Remove the plastic
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.
transfer the terminal ID to each wire (ie. + , - , AC , AC).
the proper ID is very important since the Onan will not operate with
wires & the wires are very hard to trace for ID. Now individually
the wires from the base (relive tab on each wire terminal from the
engagement side & push terminals out the rear).
drill 1/4" holes for each wire. Slide the wires thru the proper
& attach/slide on the 4 wires to the BR. Slide the BR &
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
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
BR that I use.Duane
Onan Bridge Rectifier Replacement--
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 works....so 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) &
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
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
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. $25
When I changed out the filter on my Onan today I noticed that the rubber hose (duct) that goes from the filter housing to the carb was split. I had never noticed this before as it was split along the bottom side and not visible from above. I also couldn't find the Fram replacement filter so I adapted a K&N after finding a replacement hose. Click here:
to see 3 photos of how easy of a project this is. I used
P/N RU-0810, and Gates radiator hose 20457.
BTW, the whole project costs less than the OEM air filter from Onan/Cummings.Steve F.
"Do not start your Onan while it is extended, it will break the starter bracket"
John's Onan was doing fine until he extended it and tried to start it. Then all H!@#$ 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
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
loose. Sometimes one or more of the 4 rubber mounts might be
and need to be replaced.
New rubber mounts
Thanks John Bush.
Onan Replacement Starter Information
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.
Patterns in Santa Ana California has a high strength steel replacement
Onan Starter bracket for about $35. This bracket will not
with the replacement Starter & will never break (well almost
About 1/3 cost at Onan.. It is a directly replacement starter
may have a slight metal boss interference with the OEM starter
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)
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
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
Ignition power. Do yourself a favor & disconnect the wires
to the Onan Voltage Regulator (Charger) for the purpose of better
on the Onan Control Board. The AC voltage going to the Voltage
is also used by the control board to tell when the Onan is
A faulty Voltage Regulator can & does load down the voltage to the
point that the control board will not function properly for operation
the Onan. I found this out several years ago when my Onan would
start in cold weather. Disconnected the wires at the voltage
& all is well. The AC voltage between Terminal 8 & 11
be 30 +/- 2 volts AC. When it drops below 26 volts you are headed
for Onan Run Problems.
Remove the wires
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
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