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Onan: 7.5kw YD gen end needed

MtndawgNV

Registered
First, I want to thank everyone on this forum for information I have used over the years. I’ve not posted but have researched and learned a lot, as well as fixed a lot due to the knowledge found here.

Now I’m in need and can’t resolve it myself.

The gen is an 7.5 MDJE-3CR/22 68AD, ser: H790443266

I’m looking for a good gen end or adapted newer end or other options.

I’m currently located in Titusville Florida.

The bullet story goes like this...
-saltwater leak
-my clean up was not enough
-old dirt plus saltwater = no good
-have manuals and tested myself
-main and exciter now at rewind shop, there advice is to source another
-virus issues are slowing my resolution of this issue

Thanks in advance for all the info coming my way, and maybe help for others as well.
 

JohnnyC

Subscriber
Last Subscription Date
03/18/2020
I can only speak for the land versions for the DJB, DJC, JB and JC, but most likely may be the same for the marine versions too. Don't limit your search specifically for a 7.5kw YD generator end. Last year I took a 12.0 kw YD from a DJC and bolted it to my DJB. It was a direct bolt on without any issues what so ever. The YD's stack was only slightly physically longer as expected. If I run the DJB's motor to full capacity which was meant for a 6.0kw YD, it will never overburden the 12.0kw YD.

JohnnyC
New Jersey
 

MtndawgNV

Registered
I can only speak for the land versions for the DJB, DJC, JB and JC, but most likely may be the same for the marine versions too. Don't limit your search specifically for a 7.5kw YD generator end. Last year I took a 12.0 kw YD from a DJC and bolted it to my DJB. It was a direct bolt on without any issues what so ever. The YD's stack was only slightly physically longer as expected. If I run the DJB's motor to full capacity which was meant for a 6.0kw YD, it will never overburden the 12.0kw YD.

JohnnyC
New Jersey
This is great info, thanks. I have been limiting my searching a bit and haven’t really found much info on what will interchange, bolt pattern wise. I am open to any option at this point and will broaden my search. I’ll also try some more detailed searches here, although I haven’t hit the right data yet, I’m sure it’s out there.
 

Max Thompson

Sponsor
Last Subscription Date
09/03/2019
I am not sure, but I think any YD end up to 15 KW will bolt up to your engine. The major differences in the marine versions are in the engine, not the gen-end. This does not make a 3-C YD end any easier to find though. You may find a complete JB with engine problems long before you find a white (marine) gen-end by itself.
 

JohnnyC

Subscriber
Last Subscription Date
03/18/2020
The believe only differences in the YD family would be the 4 wire vs. 12 wire, but other than that as Max stated any YD up to 15 kw will bolt on. If your boat (or land application) requires only 120 or 120/240 then either should work for you.

JohnnyC
New Jersey
 

MtndawgNV

Registered
I am not sure, but I think any YD end up to 15 KW will bolt up to your engine. The major differences in the marine versions are in the engine, not the gen-end. This does not make a 3-C YD end any easier to find though. You may find a complete JB with engine problems long before you find a white (marine) gen-end by itself.
Thanks for that info and you are right, finding an end is not easy. As for a complete generator, I have found a couple but my problem is I’m on a sailboat so space to do the work is difficult, although not impossible.

this may be a stupid question...you mentioned “white (marine)”. There is no difference, mechanically or electricalily, is that correct?
 

MtndawgNV

Registered
The believe only differences in the YD family would be the 4 wire vs. 12 wire, but other than that as Max stated any YD up to 15 kw will bolt on. If your boat (or land application) requires only 120 or 120/240 then either should work for you.

JohnnyC
New Jersey
Thanks to you and Max.

To clarify, by “either should work”, you mean 4 or 12 wire right? Sounds right to me. I am now hunting for what y’all have advised.
 

JohnnyC

Subscriber
Last Subscription Date
03/18/2020
Thanks to you and Max.

To clarify, by “either should work”, you mean 4 or 12 wire right? Sounds right to me. I am now hunting for what y’all have advised.
A 4 wire will give you only 120/240 AC 1 phase whereas a 12 wire will give you the same plus more voltage combinations 1 and 3 phase.
To further show you the YD for the DJ series in its parts from salvage to restored, please check out the pictures below. The YD in the pictures was salvaged from a 12.0 DJC and transplanted into a DJB with absolutely no incompatibility problems. Does your YD look like the YD in the picture except for color? I wonder about the engine to generator adapter. Can you take detailed pictures for the experts to see? I'm more or less at grasshopper level here as this is a hobby for me (and loving every minute of it). There are a few factory trained professionals here that can offer sound advice.

JohnnyC
New Jersey

The picture below shows the DJC that the YD head came from. The motor had a snapped crankshaft and left to rust for several years outside.



In the process of removing the YD.
000.jpg

The stack was fully reconditioned and painted to look like new. Notice the 4 heavy gauge white wires? That tells me it is a 4 wire YD.
005.jpg


Rotor too
002.jpg

Installing the 12 DJC YD generator onto a DJB-MS (2 cylinder diesel)
003.jpg

Heavy work done. Fits perfectly. This is a 4 wire generator - 4 heavy white wires coming out of the YD (looks like 3, but there is 4). A 12 wire YD will have 12 white wires.
004.jpg
 

Ben Clarke

Registered
My concern would be whether or not a non-marine gen end could pose an explosion threat.
If there is no chance of exposure to volatile gases then you are good to go. The boat is large enough to have a generator this size does it sit in an engine room next to an auxiliary engine? Does anyone know if a marine generator end differs from a non-marine generator end in regards to shielding? BBC is quite knowledgeable in this area maybe he will chime in.
What ever you do stay safe.
 

MtndawgNV

Registered
A 4 wire will give you only 120/240 AC 1 phase whereas a 12 wire will give you the same plus more voltage combinations 1 and 3 phase.
To further show you the YD for the DJ series in its parts from salvage to restored, please check out the pictures below. The YD in the pictures was salvaged from a 12.0 DJC and transplanted into a DJB with absolutely no incompatibility problems. Does your YD look like the YD in the picture except for color? I wonder about the engine to generator adapter. Can you take detailed pictures for the experts to see? I'm more or less at grasshopper level here as this is a hobby for me (and loving every minute of it). There are a few factory trained professionals here that can offer sound advice.

JohnnyC
New Jersey

The picture below shows the DJC that the YD head came from. The motor had a snapped crankshaft and left to rust for several years outside.



In the process of removing the YD.
View attachment 386601

The stack was fully reconditioned and painted to look like new. Notice the 4 heavy gauge white wires? That tells me it is a 4 wire YD.
View attachment 386611


Rotor too
View attachment 386603

Installing the 12 DJC YD generator onto a DJB-MS (2 cylinder diesel)
View attachment 386604

Heavy work done. Fits perfectly. This is a 4 wire generator - 4 heavy white wires coming out of the YD (looks like 3, but there is 4). A 12 wire YD will have 12 white wires.
View attachment 386605
good pics.

Yes, mine looks identical, other than white. Also my bell housing looks to be clocked 180. That is nice looking work you’ve done. I’m starting to get excited about restoring this thing, thanks for the motivation.
 

MtndawgNV

Registered
My concern would be whether or not a non-marine gen end could pose an explosion threat.
If there is no chance of exposure to volatile gases then you are good to go. The boat is large enough to have a generator this size does it sit in an engine room next to an auxiliary engine? Does anyone know if a marine generator end differs from a non-marine generator end in regards to shielding? BBC is quite knowledgeable in this area maybe he will chime in.
What ever you do stay safe.
That’s a great thought on the possible differences. I’ve done some work on other intrinsically safe electronics. These don’t look to be TOO protected. I look forward to experts chiming in On this one.

As for the boat, yes, it sits in the engine room. The boat is a Gulfstar 47, if anyone was wondering.
 

JohnnyC

Subscriber
Last Subscription Date
03/18/2020
As for the bellhousing, let me show you a few pictures of the bellhousing and behind it. It appear that my bellhousing only bolts in one way, but I would expect your bell housing to be different. What I believe to be important is the slightly tapered crankshaft nose. For the land versions of the J series, they all seem to be the same, but not sure about the marine version. I don't see why not, but I never had a marine J series set so I am laying out all the cards on the table to look into to avoid any bad/incorrect advice. I hope these pictures help. Sometimes a picture is worth a thousand words.


JohnnyC
New Jersey

The picture below shows my DJB without the bellhousing bolted onto it.
002.jpg


The picture below shows the bellhousing bolted onto the DJB-MS. You may need to flip back and forth to see where the bellhousing bolts (4) are located.
001.jpg

Another view
000.jpg

Another view
00000000000000000.jpg
 

zuhnc

Subscriber
Last Subscription Date
12/08/2019
The generator adaptor (bell housing) might be different for the marine version, due to cooling air outlet if in a sound shield. The remainder of the generator (rotor, stator, end bell, etc) are the same and will interchange. No difference in components, i.e., ignition-proof (as found in gasoline-fueled boats), being diesel. zuhnc
 

MtndawgNV

Registered
As for the bellhousing, let me show you a few pictures of the bellhousing and behind it. It appear that my bellhousing only bolts in one way, but I would expect your bell housing to be different. What I believe to be important is the slightly tapered crankshaft nose. For the land versions of the J series, they all seem to be the same, but not sure about the marine version. I don't see why not, but I never had a marine J series set so I am laying out all the cards on the table to look into to avoid any bad/incorrect advice. I hope these pictures help. Sometimes a picture is worth a thousand words.


JohnnyC
New Jersey

The picture below shows my DJB without the bellhousing bolted onto it.
View attachment 386637


The picture below shows the bellhousing bolted onto the DJB-MS. You may need to flip back and forth to see where the bellhousing bolts (4) are located.
View attachment 386638

Another view
View attachment 386640

Another view
View attachment 386641
A picture is sure worth a thousand words. I’ve done some rough scaling on your pics and all looks to be the same as mine. The taper is the hardest to measure/scale but as far as I can tell it’s very close if not the same.

The bell housing is slightly different. The air passage on mine is 180 degrees out from your pics. The relief for the wires is in the same place though.

Ok, here is the BIG question... you wouldn’t want to sale that end would you? I believe I already know the answer, but had to try.

Just for fun, here’s a close up for an idea of how bad this thing got.

2D546874-7B03-4DF0-B16F-F80A8C2F5803.jpeg2D546874-7B03-4DF0-B16F-F80A8C2F5803.jpeg
 

MtndawgNV

Registered
Tha
The generator adaptor (bell housing) might be different for the marine version, due to cooling air outlet if in a sound shield. The remainder of the generator (rotor, stator, end bell, etc) are the same and will interchange. No difference in components, i.e., ignition-proof (as found in gasoline-fueled boats), being diesel. zuhnc
Thanks for clarification.
 

JohnnyC

Subscriber
Last Subscription Date
03/18/2020
A picture is sure worth a thousand words. I’ve done some rough scaling on your pics and all looks to be the same as mine. The taper is the hardest to measure/scale but as far as I can tell it’s very close if not the same.

The bell housing is slightly different. The air passage on mine is 180 degrees out from your pics. The relief for the wires is in the same place though.

Ok, here is the BIG question... you wouldn’t want to sale that end would you? I believe I already know the answer, but had to try.

Just for fun, here’s a close up for an idea of how bad this thing got.

View attachment 386708
That will clean up well with a little soap and water (and maybe a media blaster and a prayer). Below are 2 pictures of what mine looked like when I got it and the last picture after a cleaning. Don't forget to install a new bearing. If you need information on it, just ask. Price for a new bearing will range between $10 to $13 for an American or Japanese bearing. $4 for a cheap Chinese bearing. DO NOT by Chinese bearings. They are crap.
Thanks for the offer, but my YD is already installed and running fine.

JohnnyC
New Jersey

000.jpg

001.jpg

00000000000000000.jpg
 
Last edited:

BigBlockChev

Subscriber
Last Subscription Date
07/06/2019
The main difference between the marine and stationary YD gen ends is the air outlet for the cooling air. In the stationary units it blows out the rear in the marine units it blows out the front to accommodate the Soundshield air passages as Zuhnc indicated . Otherwise there is no difference in the stator , rotor , or exciter coils. Be careful if looking at 4 wire stators as they may be 3 phase, a 120/240V stator will have 2 separate coils T1-T2 and T3-T4 . A 3phase stator will have L0-L1-L2-L3 all of which will have continuity with each other. 12 Lead stators no problem with that but extremely rare if not non existent. Marine generators suffer from an abundance of corrosion so careful physical inspection of the coils is wise, stationary gens not so much, though the exciter coils still fail frequently , a milliohm test of all of them is a good idea and maybe a megger test as well. Cheers Dan
 

JohnnyC

Subscriber
Last Subscription Date
03/18/2020
The main difference between the marine and stationary YD gen ends is the air outlet for the cooling air. In the stationary units it blows out the rear in the marine units it blows out the front to accommodate the Soundshield air passages as Zuhnc indicated . Otherwise there is no difference in the stator , rotor , or exciter coils. Be careful if looking at 4 wire stators as they may be 3 phase, a 120/240V stator will have 2 separate coils T1-T2 and T3-T4 . A 3phase stator will have L0-L1-L2-L3 all of which will have continuity with each other. 12 Lead stators no problem with that but extremely rare if not non existent. Marine generators suffer from an abundance of corrosion so careful physical inspection of the coils is wise, stationary gens not so much, though the exciter coils still fail frequently , a milliohm test of all of them is a good idea and maybe a megger test as well. Cheers Dan
Dan, EXCELLENT advice on the 4 wire 3 phase and all!!

JohnnyC
New Jersey
 

MtndawgNV

Registered
Dan, EXCELLENT advice on the 4 wire 3 phase and all!!

JohnnyC
New Jersey
Agreed, that is excellent advice, and all the other advice.

I‘m still in the process of sourcing all the needed parts. I have found some up to this point. I’m struggling to get my old parts back from the re-wind shop in Ft Lauderdale as they seem to be closed for virus issues.

I‘ll keep the updates coming as I can.

any advice on sources would be welcome as well.
 

MtndawgNV

Registered
Okay, small update here.

i was able to get to the re-wind shop and pick up the parts (main and exciter rotor and stato). The shop has told me on the phone and marked all my parts as “bad”. They did clean them up, all grease and gunk is gone but still quite rusty. For fun i started testing and so far everything is in spec, minus the rotating rectifie diodes.

I’m going to do some deep cleaning and more in-depth test to confirm my casual tests.

I have a source for the diode sets as I have replaced them before but I’m having trouble sourcing an AMERICAN made bearing. Does anyone have a good source? I found bearings and have an e-mail out as to manufacturin, but have not heard back yet.

image.jpg
 
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