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Onan 7.5 MDJE 3CR/2268AB New Toy


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  #1  
Old 04-02-2017, 10:21:11 PM
PnishrPW PnishrPW is offline
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Default Onan 7.5 MDJE 3CR/2268AB New Toy

Picked this up off CL a few days ago under duress, ( nah, been looking for a D/JB or DKD reasonable for awhile) for $120. First diesel Onan I've owned, maintenanced a couple in the past but that's it.

Unit is 99.9% complete and not in bad shape. Main issue: very low compression in both holes. Barring over the motor by hand very slight resistance is felt on compression strokes. No strange noises were heard from the bottom end. Oil is used but clean and doesn't smell hot/burnt.

Raw water pump is fried, fresh is questionable but nice green antifreeze in heat exchanger. Glow plugs show resistance (.9 on manifold/1.8 on other 2). Solenoid on starter seems to be hung up, going to pull starter if I can get compression. Fuel solenoid moves freely under finger pressure, as does gov/inj pump. Barring over the motor, diesel drips from fuel return ditto when prime lever is depressed.

It has a un-potted vr 21 and other than a couple of cut wires in the AC output box (cover is MIA...) overall electrical seems intact and in good condition. It has hi temp and lop switches. Start / stop & pre-heat switches feel good. Control box was someones pantry but no damage noted. Haven't put power to it yet, see no need till I have compression.

Done so far: not damn much... Looked it over a bit, started hitting hardware with PB. Vacuumed it some, baseplate/control box etc. Going to pull valve cover and see if it has stuck valves (Thx BigBlockChev) first, go from there. Hoping for something stupid wrong.

5hrs before I got this I scored 4 GC-2 6v golf cart batteries in decent condition (test 70-80%) for price of cores, was wondering what I was going to do with them...

More pix next post.
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Old 04-02-2017, 10:26:21 PM
PnishrPW PnishrPW is offline
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Default Re: 7.5 MDJE 3CR/2268AB New toy

Some more pix:
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Old 04-02-2017, 10:32:22 PM
PnishrPW PnishrPW is offline
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Default Re: 7.5 MDJE 3CR/2268AB New toy

How I found it, we broke his "liftin' tree" loading it. ""It only weighs about 300#"" sellers words, not mine...
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Old 04-03-2017, 12:37:00 AM
Ray Lynch Ray Lynch is offline
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Default Re: 7.5 MDJE 3CR/2268AB New toy

Look like it could be a nice set.
Good luck with it.
Ray
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Old 04-03-2017, 07:04:21 AM
Kevin K Kevin K is offline
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Default Re: 7.5 MDJE 3CR/2268AB New Toy

Good deal. You got it for a reasonable price considering it's condition. Far too many sellers think that cold hunk of metal sitting on the ground is worth a fortune.
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Old 04-03-2017, 08:14:07 AM
PopsGarage PopsGarage is offline
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Default Re: Onan 7.5 MDJE 3CR/2268AB New Toy

WOW, great unit looks 100% better than the 1966 MDJB that I brought home in 1999 yours is all there mine had parts removed. Good luck with your project.

Bob
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Old 04-04-2017, 01:07:16 AM
PnishrPW PnishrPW is offline
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Default Re: Onan 7.5 MDJE 3CR/2268AB New Toy

Thx, I figured for the price I couldn't get hurt to bad ( unless I drop it on my toes... ). I spent a few minutes on it today, mostly spraying PB. Raw water pump may not be as bad as I initially thought, got it off today. If I end up using this gen I won't be using it. I'm going to try to get the valve cover off soon and check valve action, maybe I get lucky. If it has stuck valves I'll try to free them up without pulling the head.

Been spending some time researching/reading manuals, I can't seem to find a build sheet. If anyone has one could I please get a copy? Thx, D
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Old 04-04-2017, 03:20:16 AM
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Default Re: Onan 7.5 MDJE 3CR/2268AB New Toy

Here ya go.
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Old 04-05-2017, 01:13:49 AM
PnishrPW PnishrPW is offline
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Default Re: Onan 7.5 MDJE 3CR/2268AB New Toy

Thx Onanparts!

Got to spend a few minutes playing with it today: I turned it over 3-4 times by hand - compression has a little more resistance now. I got the valve cover off, valves not stuck but seem to have significant lash. Next I'm going to check/set lash, maybe check lift. Didn't even mess up the gasket, surprisingly clean inside.

Got the starter almost out, small wire on solenoid given me da blues... Been pre treating most hardware since I got it with PB blaster, usually doesn't let me down. Actually, most all the hardware has been surprisingly drama free. Pulling the starter because solenoid seems stuck, would rather do this diag/repair on the bench. If I can get the starter serviceable, I'll try to fire it up.

Just for giggles, I pulled the glow plugs and shot some PB in. They actually came out nice and easy.

For now it still sleeps with the fishes...
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Old 04-05-2017, 05:04:34 PM
TLB01 TLB01 is offline
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Default Re: Onan 7.5 MDJE 3CR/2268AB New Toy

Looks like it might be relatively low hour and had plenty of time to sit around. Might want to crack open the control box and check for mouse houses. And seeds in the gen end.

Haha, you already did!
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Old 04-05-2017, 06:21:54 PM
len k len k is online now
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Default Re: Onan 7.5 MDJE 3CR/2268AB New Toy

Looks nice, control box looks pretty pristine too.

Could still be the valve seats cruddyed up

Quote:
Originally Posted by PnishrPW View Post
Glow plugs show resistance (.9 on manifold/1.8 on other 2).
Interesting ,,, at 12V that's ~27 amps total.
On a DJB someone tested it and measured 50 amps total ( I assume that was 12 VDC.)
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Old 04-05-2017, 07:47:56 PM
Richard L Richard L is offline
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Default Re: Onan 7.5 MDJE 3CR/2268AB New Toy

Howdy,
Doesn't look to be in that bad of shape.
Have manuals and a Onan Training Manual that was given out at a class in Sea when these came out in the 70,s, can e mail if you need info.

mvamaunet@gmail.com
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Old 04-05-2017, 08:23:49 PM
Combustor Combustor is offline
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Default Re: Onan 7.5 MDJE 3CR/2268AB New Toy

If it has stood a while there could just be grit and carbon lodged on valve seats, so worth taking a soft hammer or wood block and with valves closed, smack each rocker arm above the valve stem to dislodge crud,and then check clearances. A small shot of oil in each intake port and you may well have it running.
Those DJ series do need good glow plugs and 30 seconds or more of glow time to fire up. No starting fluid if there is an intake heater. Regards,
Combustor.
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Old 04-05-2017, 09:05:25 PM
MBB MBB is offline
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Default Re: Onan 7.5 MDJE 3CR/2268AB New Toy

Try 932-0405 for training manual on http://www.twinslan.net/~n0nas/manuals/onan/

As well as other manuals.
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Old 04-05-2017, 10:28:25 PM
MBB MBB is offline
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Default Re: Onan 7.5 MDJE 3CR/2268AB New Toy

Here is the wiring diagram according to the build sheet OnanParts posted.
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Old 04-05-2017, 10:44:56 PM
PnishrPW PnishrPW is offline
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Default Re: Onan 7.5 MDJE 3CR/2268AB New Toy

Thx guys, I don't have a lot of time to spare for this project but you all provide great advice and motivation! I'm picking away at this in literally few minute increments... ex: today I had to run back to my shop twice during the day, each time I spent a 2-3 min spaying and working the small terminal on the starter. Second time it worked loose and came off clean.

After work I had about 30 min before heading to a service call. I pulled the starter and got it on the bench. Pulled the pin between solenoid and linkage, arm and solenoid both slightly stuck. Removed solenoid and freed it up, ditto for starter fork. Going to open solenoid and check contacts and plunger, same for starter - brushes etc. Both are soaking in PB, starter thru bolts are loose - solenoid not so much... Memo to self : buy some tiny a$$ cotter pins... Located a solenoid locally, $36 if I need one. Was quoted $325 for a rebuild!

Also going to pull end bell and have a look see at the bearing / brushes etc. Screws soaking now.

Len, I forgot to factor in .4 ohms for lead resistance - mea culpa!

Thx for info Mike, looking like I may need it soon. I've started a file for the relevant docs, I am having trouble extracting schematics / diagrams from pdf's, can't seem to get it right.
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Old 04-06-2017, 09:07:54 PM
rmchambers rmchambers is offline
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Default Re: Onan 7.5 MDJE 3CR/2268AB New Toy

If you need the raw water pump I may have a kit or two to repair that with, not sure if the impellers are any good though. If this is not going back into a boat I'd do away with the raw water anything and use the fresh water loop to go to a radiator or some other way to dump the heat. Less drag on the engine that way too. Treating the whole thing with PB is a good idea, a lot better than trying to find broken screws/bolts etc.

Robert
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Old 04-07-2017, 11:34:59 AM
PnishrPW PnishrPW is offline
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Default Re: Onan 7.5 MDJE 3CR/2268AB New Toy

We have achieved starter! Got the starter opened up and checked the brushes, they look recent. Commutator needs attention but is serviceable for now. I couldn't get the endcap off the solenoid so I didn't check the contacts. I re-assembled everything and cleaned the terminals as best I could. Put some cables on it and it WORKS. Little balky first couple of tries, but seems to be ok now. Got it re-installed.

Pulled the gen end cap, little rough but nothing jumps out at me. Going to lube the bearing and check field resistance.

Looking like I may try to start it tomorrow, need to disconnect the vr, and check engine electrical first. I've probably missed something on the pre-flight, if I have please let me know...

Robert, I appreciate the offer - but the raw water pump won't be going back on. Bearings seem good, I think what I initially felt was the impeller disintegrating. It feels better now... If someone needs it, PM me! The heat exchanger may also be up for grabs, unsure right now.
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Old 04-09-2017, 01:10:45 PM
PnishrPW PnishrPW is offline
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Default Re: Onan 7.5 MDJE 3CR/2268AB New Toy

Going to drive out to shop shortly, ended up working till 9 last night... Gotta find out if Schrodinger's generator is alive or not. If it's alive, I'm guessing it'll be okay to run for 5 min or so with no active cooling? Fresh water system is intact and full of nice green coolant, but no belt. Ambient temperature - 50ish.

Would anyone happen to know what size / type of belt is needed for the fresh water pump? Will only be using 1 pump in stock location.

Any (and all!) last minute advice about waking the beast would be greatly appreciated! Thx, D
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Old 04-09-2017, 04:35:36 PM
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Default Re: Onan 7.5 MDJE 3CR/2268AB New Toy

This is what is on one of mine, could go 1/2"shorter to be in the middle of the adjustment range. Should be OK to run for a few mins with no cooling. These diesels don't produce much heat at no load. If the heat exchanger is still in place you can run a garden hose through it instead of a pump. Use the manual lever on the pump to purge the fuel till you get no bubbles at the return line , use a piece of clear hose on the return line and leave an up facing loop to be able to see the fuel flow and air bubbles. Glow for a minute for easiest starting. Use a big well charged battery and bolt the cables on rather than using jumper cables if at all possible. So, no air in lines , BFB, and glow for a minute and it should start. Cheers Dan
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