30 year old Onan MDKD "overhaul"

[Mischief Managed]

I removed my Onan 8.0 MDKD genset from my boat earlier this week. It normally resides under the cockpit sole and is not very accessible for service, for a biggish person like me. It has only had basic maintenance since new and after suffering a seized alternator over the Summer, I decided to go through it and make it more reliable over the Winter.


I will be replacing:
Starter (it's a nightmare to access in the boat and a new one from DB Electric is only 90 bucks)


Heat Exchanger (another nightmare to access and new is only 300 bucks from Lenco)


All integrated hoses and hose clamps (150 bucks)


External hoses and hose clamps, except exhaust hose, which was new in 2019 and is still in great shape. (100 bucks)


Coolant pump and thermostat (55 bucks)


Fuel filters


Oil and oil filter


Breather element (3 bucks)


Glow Plugs (16 bucks)


The belt and alternator are new already 75 buck from DB Electric and local parts store.


I will be rebuilding the raw water pump with a $220 kit.


I will be cleaning up all the corrosion I can get to and painting everything, including the sound shield.


It has a Kubota D950 3 cylinder diesel, so the engine is very rugged and reliable and I don't plan to open it up. I don't plan to do anything with injectors or injector pump, it runs fine and only has 1300 hours, plus they are easy to access.


Was thinking I should also replace the anti-vibration mounts, and generator bearings. Is there anything else I should do while it's out and easy to work on?



It really pays to shop around for parts. Cummins/Onan have ridiculous pricing. For instance: They want 40 bucks each for NGK 6325 glow plugs that I can get from Advance Auto parts for $5.30 each. DB Electric sells a brand new alternator for 68 bucks, Cummins/Onan gets almost $800 for that part. OEM HE is $900, Lenco sells theirs for $300.

 

[Gdavid]

I removed my Onan 8.0 MDKD genset from my boat earlier this week. It normally resides under the cockpit sole and is not very accessible for service, for a biggish person like me. It has only had basic maintenance since new and after suffering a seized alternator over the Summer, I decided to go through it and make it more reliable over the Winter.


I will be replacing:
Starter (it's a nightmare to access in the boat and a new one from DB Electric is only 90 bucks)


Heat Exchanger (another nightmare to access and new is only 300 bucks from Lenco)


All integrated hoses and hose clamps (150 bucks)


External hoses and hose clamps, except exhaust hose, which was new in 2019 and is still in great shape. (100 bucks)


Coolant pump and thermostat (55 bucks)


Fuel filters


Oil and oil filter


Breather element (3 bucks)


Glow Plugs (16 bucks)


The belt and alternator are new already 75 buck from DB Electric and local parts store.


I will be rebuilding the raw water pump with a $220 kit.


I will be cleaning up all the corrosion I can get to and painting everything, including the sound shield.


It has a Kubota D950 3 cylinder diesel, so the engine is very rugged and reliable and I don't plan to open it up. I don't plan to do anything with injectors or injector pump, it runs fine and only has 1300 hours, plus they are easy to access.


Was thinking I should also replace the anti-vibration mounts, and generator bearings. Is there anything else I should do while it's out and easy to work on?



It really pays to shop around for parts. Cummins/Onan have ridiculous pricing. For instance: They want 40 bucks each for NGK 6325 glow plugs that I can get from Advance Auto parts for $5.30 each. DB Electric sells a brand new alternator for 68 bucks, Cummins/Onan gets almost $800 for that part. OEM HE is $900, Lenco sells theirs for $300.

Sounds like you will have a pretty serviceable unit when this scope is done. I have one of these units in my garage now that I inherited as a free project, it wasn't running due to low compression, I replaced the head gasket using the Kubota part, rebuilt the raw water pump and refinished the base and sound enclosure. The pan/base that the generator mounts to was pretty nasty due to years of slow raw water leaks, I refinished it using POR-15. I did not replace anything else. I will replace the glow plugs, thanks for heads up on Advance Auto for a source for them. My boat came with an old MDJA that runs everything I need it to with careful load management but I intend to install the MDKD within the next season or two unless the little single cylinder dies before then.

 

[Bmarler]

i'd love to pull mine and do the same, but it's under the salon floor. my access is probably a little better than yours though. having it up on a workbench would be awesome.
does the generator end have brushes? i haven't been in one to see. (yet) if it does, i'd look at those.
i have all the floors up right now for re-wiring, and i see some corrosion on mine that i'm going to attack while the access is good.
i'll be looking for new anti vibration mount too. mine is probably a bit older. (mdje) you're right about cummins/onan prices, they're out of line.

 

[jgwinks]

I put a DB starter on the Universal 5411 on one of my previous sailboats and it worked well for the couple of years I still had it. It was easy to access and I could have bought at least four of them for the cost of the real one. Cheaper even than rebuilding it. But if it's impossible to get to with the engine installed, I think I'd want to go with a higher quality unit. Probably not $800 better, just not bargain basement. If it quits working and you have pull the genny out again to replace it, you're going to wish you hadn't done that. I just had the starter rebuilt for my 1973 Onan by a local shop for only $180. New brushes, solenoid etc and all cleaned and painted. Still the OEM unit at about the same cost of the Chinese knockoff. The replacement through Cummins which is not the same starter but is supposed to work was $850. $160 for the knockoff version. Neither one of the replacements looked anything like the original so I didn't want to go that way even though they were supposed to fit. Apparently the original type hasn't been made for 20 or 30 years.

 

[Mischief Managed]

I ordered a new generator head bearing, it's a generic 6305-2RS part, so no need to spend a fortune on the Onan part. I got three NGK 2031 (same as NGK 6325 or Y-103V, it seems) glow plugs from Napa for 15 bucks. I have ordered the vibration mounts, they are OEM only and 37 bucks each. I cannot find any brushes in the parts book. I will look for them when I pull it apart and if they are worn, I ill buy and install new ones.

 

[Mischief Managed]

I put a DB starter on the Universal 5411 on one of my previous sailboats and it worked well for the couple of years I still had it. It was easy to access and I could have bought at least four of them for the cost of the real one. Cheaper even than rebuilding it. But if it's impossible to get to with the engine installed, I think I'd want to go with a higher quality unit. Probably not $800 better, just not bargain basement. If it quits working and you have pull the genny out again to replace it, you're going to wish you hadn't done that. I just had the starter rebuilt for my 1973 Onan by a local shop for only $180. New brushes, solenoid etc and all cleaned and painted. Still the OEM unit at about the same cost of the Chinese knockoff. The replacement through Cummins which is not the same starter but is supposed to work was $850. $160 for the knockoff version. Neither one of the replacements looked anything like the original so I didn't want to go that way even though they were supposed to fit. Apparently the original type hasn't been made for 20 or 30 years.

I have had great luck with stuff from DB Electric for at least a decade, maybe more. I can replace the starter with the genset in the boat, it's just SOOO much easier when it's out... I will be carrying the old starter as a spare.



I pressed out the bearings in my OEM alternator and replaced them with new bearings (6301ZZ in case anyone wants to know) and I carry the old alternator as a spare too. The DB Electric alternator is part number 400-58002.

 

[Gdavid]

That alternator looks like a toy, such a cute little thing.

 

[Mischief Managed]

That alternator looks like a toy, such a cute little thing.

It's not built like a car alternator, it uses magnets instead of field coils and it's tiny, maybe softball-sized. It only makes 10 amps max. I only need it for keeping tension on the belt, my 3 bank charger charges the genset battery when the genset is running. That said, it is connected and does charge the battery, but it's superfluous, electrically.

 

[jgwinks]

I have had great luck with stuff from DB Electric for at least a decade, maybe more. I can replace the starter with the genset in the boat, it's just SOOO much easier when it's out... I will be carrying the old starter as a spare.



I pressed out the bearings in my OEM alternator and replaced them with new bearings (6301ZZ in case anyone wants to know) and I carry the old alternator as a spare too. The DB Electric alternator is part number 400-58002.

Well that sounds better, I only had a couple years experience with the one I bought. I really intended to have the original rebuilt, but the rebuild would have been quite a bit more than the DB replacement so I never did it.

 

[O C Diver]

I would consider changing the onboard fuel filter and lift fuel pump. Have a friend with a 35ish year old Westerbeke with a Japanese engine similar to the Kabota. The mechanical fuel pump failed and partially filled the crankcase with diesel fuel. Mine is electric, but would guess yours is mechanical.

I would agree with changing the end bearing on the generator. I did mine when the generator was out. It's relatively inexpensive and you will probably never have to do it again.

Ted