Onan Generators

[Trojan]

Well as long as everyone has there brain tuned in on generators. I need some help too. Where can I get a manual for a 1973 7.5 KW Onan model MDJE 3CR 2268B. It runs great. It just does not want to start very quick. You have to crank it way to long to get it to start. There are 2 glow plug switches at 2 differant locations. 1 On the unit in the bilge and 1 on the main panel in the solon. It seems to start quicker when you use the unit glowplug switch. The colder it is the harder it is to start. I've had this trouble on a tractor once. The wire size on the glowplug was to small for the length run and was lowering the voltage because of the resistance. Do you think the glowplug could be going bad. This is a 2 cylinder and only 1 cylinder has a glow plug I was told. The unit has about 3000+ HRs. as best I can tell. Any ideas or thoughts out there. BILL

 

[bigbill]

anybody know how to tell the year of an onan genset by the model or serial number. the boat i am buying has a newer onan but the previous owner doesn't know the year. model mdkad 4482038c serial e000108430 thanks for any help bigbill

 

[REBrueckner]

I've never heard of an ONAN with only one glow plug, unless it's in the air intake. My four cyclinder 1972 12 kw ONAN has a glow plug in each cylinder, plus a heat coil visibly glowing red hot in the air intake during preheat. It's extremely rare for a glow plug to gradually go bad..they either glow or they don't.

A simple fast test is while at the genny tap the wire connector to the glow plug connection point with preheat "on" ...a small spark indicates its ok; no spark means the glowplug is burned open and needs to be replaced. An absolute test is to remove the glow plug, ground the threads somewhere on the genny and look at it glow (or not) with preheat on...

Your description could also be a result of low compression. But if your genny handles a full rated load without slowing down appreciably, it's likely ok. Low compression is typically due to worn rings or valves...poor valve seats or valves needing gap adjusting.

 

[Genesis]

Compression is probably a bit down....

Check those glow plugs. They can fail open. With the glow (hold the glow switch for 5-15 seconds before lighting it off; longer in cold weather) it should fire up pretty quickly, although it will smoke like a SOB when cold due to only one cylinder having glow assist until the second cylinder comes online (a few seconds after starting)

The glow plug resistance should be very low measured to ground - glow plugs usually have "on" resistances in the area of a quarter to half-ohm and sometimes less. If its significantly higher than an ohm the plug is open and that's your problem - pull and replace it.

If the resistance looks ok then take a VOM and put it on the plug to ground circuit while you hit the glow switch. You should see 12V with it energized. If the voltage is under 11V under load you have a wiring or ground problem somewhere in the circuit (high resistance) - find and fix it.

 

[Trojan]

One of the other Captains on here has the same unit as me. He also said it would smoke like a SOB at start and it does. I never checked the glow plug. Only because when it got warmer outside the better it would start. I thought that it was hard starting only because it set for so long. Maybe the g/p is bad,it could verywell be. As soon as the weather gets above 32 degrees. I'll go to the boat and check out the glowplug. I got to find it first. I don't remember seeing it or it's wire. I've had glowplugs in our R/C engines loose there ability to glow and not be open. Maybe I should, will just buy a new g/p and stick it in there.They shouldn't cost too much should they. Bill

 

[Will]

My soon to be replaced generator is an Onan 7.5 MDJE-3CR/2268AD. The service manual describes the Preheating Circuit as follows:
“This 12 volt battery circuit consists partly of manifold heaters that raise the combustion air temperature at the intake manifold and a glow plug in each cylinder that heats the precombustion chamber for engine starting. The manifold heater and glow plugs are wired in parallel and are controlled by a preheat switch on the control box.”

I have the original set of manuals if you want them.

Will

 

[REBrueckner]

My 12KW onan. 1972, used to smoke and miss like crazy at start up..then clear and run fine after maybe 15 or 20 seconds. BUT it had one other minor sympton-it would slow a bit more than expected when heavy loads were applied. My mechanic noticed this.

It turned out that when my mechanic adjusted the valves trying to solve the above smoky start condition, he set the valves for a 15 KW which is what I told him, based on original records for my boat. A year later I became suspicous, drilled off the ONAN mfg plate, cleaned off the paint and found it was really 12KW...and the intake vales are supposed to be set .006 tighter than the 15KW!!! so the valves were sloppy loose...After correct adjustment, like magic I've had clean starts with smooth operation, no smoke, for two years....

 

[Trojan]

Will! That sounds great. I will glady pay for them and pay S/H.. Email me at hamalot@cass.net. Like I'm thinking. Maybe I have something else wrong that I'm not seeing. It really helps to ask this great group. Thanks. BILL

 

[SeaEric]

I used to have a Benz diesel 5 cyl and valve adjustment was critical, particularly in cold weather. I agree as above, get the valves properly set and then see what happens.

 

[Nonchalant1]

You can also order owners, service and parts manuals from ONAN for any model.

 

[Trojan]

I did not find a number to call for a manual for my generator on the Onan web sight. I was down to the boat and ckecked out the glowplug today. The glowplug measured 1.2 ohms. From the panel on the genset to the glowplug the voltage red 11.99 volts. From the remote switch to the glowplug the voltage read zero. I checked the switch, it was bad. I guess that explains the hard starting.
Now if I can only get a manual I will be all set. I hope.


BILL

 

[Nonchalant1]

Try Cummins-N-Power (Onan's new owner) at their HQ in Minnesota at (763) 574-5000. If they don't have it, I can get you the Onan service dept where I ordered my old manuals here in Illinois.

 

[Beckytek]

Here is the number I call for parts from Onan,
Central Parts Warehouse
1549 Bobali Dr
Harrisburg, Pa. 17104
717-986-9062

 

[Trojan]

Thanks Guys. I will give them a call.

BILL

 

[Will]

Bill,

I expect to pull the old Onan 7.5 kw out of the boat over the next 2-3 weeks. Do you still want the manuals? If so, I'll send them to you as soon as it's out of the boat.

Will

 

[Trojan]

I Sure do Will. I also got your e-mail pictures, Looks good. I went to the boat Tuesday. Must of had a senior moment I forgot the camera.


BILL

 

[Will]

Bill

Ok, I'll send them to you.

I responded to the e-mail address indicated on an earlier Generator thread of yours but sent no photos. Since I never got an email reply, I'm wondering if I have your correct email address.

Will

 

[Trojan]

WillI have been using my laptop and I can recieve email I just can't send it yet. If I get on my old computer I can send email OK. Your pictures of your radar tower came through just fine.



Bill.

 

[Trojan]

I found out what was wrong. The wire that feeds the 12v to the glowplug relay was eaten in half. I cut and spliced it. It works fine now. Tomorrow I will change out the complete wire. It had been spliced in 4 places. Not good. I also said I only have one glowplug but I was wrong. It has 2 plugs and a air heater. I just could not see them without standing on my head. Someone in a real early thread said it only had one so I did not look for the second one. I also found out that the generator can be rewired for 220 volts AC. Cool. The things you learn when you start digging.



Bill

 

[spartonboat1]

Re: Onan Generators/Two Glow Plugs!

Very interesting thread!!! At least to a limited number of us with MDJE's.

I have the exact model above, the MDJE 7.5Kw, 2268B as a 1972 model. Bench rebuilt and runs great. Too noisy for most I suspect, but an the sound is an acquired taste. I was the one (culprit?) I suspect who indicated that only one cylinder was helped and to expect lots of smoke, until the unaided cyl heated up. So a major mea culpa on that info on my part. I could have sworn that a very experienced Onan tech told me that only one cyl was aided. I double checked my typed notes based on my phone conversation with him, and the notes clearly indicate that only one cyl (#1) is aided. Very curious.

My curiosity is now very high to locate both the glow plugs and check if they both function. The Operators Manual and Parts Catalog schematics/diagrams only indicate a single plug, and then not at the installed location, but only as a separate reference.

However I did find a schematic #612-4792 that clearly calls out a BOM with 2 glow plugs (2 cyl) or 4 glow plugs (4 cyl), called out as HR's #1-5. The circuit diagram that the Manifold Heater Solenoid provides 12v+ (B+) to HR1 (Manifold Heater), and HR2 (glow plug 1) and HR3 (glow plug 2).

Frankly, until this post, I was not aware that glow plugs were installed, but I did know that the manifold heater was present. I had a hard starting issue, but the tech said that one/half of the heater plate in the manifold was open/burned out, and that installing a new heater plate (I call it the toaster oven) cured my started situation.

However, the hard starting was still somewhat intermittent, until I had some bad fuel get into the fuel filters. After all the genny fuel filters were changed out, the starting became very consistent. I rarely fails to start even down into the low 30's. But The manual is clear that lifting the pre-heat switch for one minute is required.

Manuals I have for this unit are:
>Operators Manual and Parts Catalog- MDJE Series, book #968-325,
>Technical Bulletin #T-021, Installation of Onan Marine Electric Generating Sets, Aug 1971,
>Control-Gen Set (Wiring Diagram) Schematic/Bill of Material #612-4792, update note 12-20-77
>Onan Parts and Service Centers March 1972 #F-115

I have a digital camera and could shoot some pages, or I also have an HP Scanner and could scan in some (all) of the catalogs pages.

To quote Queen, I've got egg on my face, such a disgrace...