Onan MDKBH 4KW - intermittently won´t crank

Also posted over at boatdiesel;

This is a really strange one. My genset will run fine until I shut down but seemingly randomly, when I go to start later in the day it will prime but not crank. Sometimes after a few attempts it will suddenly crank, start and run as normal. I´ve done all sorts of trouble shooting including replacing fuel filters etc and checking all connections but no joy. I can´t work it out. It seems as though there is some relay (or similar) that intermittently decides not to play but will then suddenly come to life.

It´s really annoying as I can´t handle issues that I can´t diagnose and resolve let alone an unreliable genset.

Any help or advice would be appreciated.

Lots of help on Onan generators on Smokstak.com. Smokstak>Vintage Electrical Equipment>Onan Generators. I use boatdiesel for my 3208’s, but have found Smokstak much better for my MDKD. I assume you’ve pulled off the + and - cables and cleaned them thoroughly. If no help, do a few plug-unplug cycles with all the spade connectors on the shutdown sensors and fuel solenoid to clean them. After that it gets more complicated, and the knowledgeable guys at Smokstak can steer you better than I can. There is a start relay in the control box, and I believe the gap is adjustable and the contacts can be cleaned, but that’s all above my pay grade.

If you don’t have your manuals, they’re available here http://www.skilledcrafting.com/onanfiles/

When you say it won't crank, I assume you mean you get no reaction from the starter. If that is the case it's a simple test and simple fix.

Next time its a "No Go" take a wooden hammer or fairly heavy wooden stick and give the starter a fairly hard tap. If it then starts you need a new starter. Simple!

Don't be afraid to hit it pretty hard or hit it several times.

I'm betting you will find the problem.

pete

Intermittent starter problems probably mean the contact points in the solenoid are burnt and pitted. There are 2 points and a disk that touches both when the solenoid is activated. Usually the points and disk are copper. The disk turns slightly each time you start, making the disk last longer.
If your ambitious, take the solenoid apart and file the points and disk with a flat file.

The reason it's intermittent is sometimes the points line up on a less pitted place and other times a badly pitted place. Because of the high amp draw, a poor contact will not let enough current flow to turn the starter. Starters usually burn out their windings after a long period of operation with poor contacts.

If what you mean by "not crank" is that it won't turn over, I think Lepke has hit the nail on the head.

That sounds to me like a starter or ignition relay/solenoid/contactor problem and, as Lepke writes, it is most likely on the starter solenoid.

The good news is that those solenoids are relatively inexpensive and can just be swapped without needing to rebuild the whole starter. Just get the model number and order one from the web or pick one up at a local electrical shop. They can be from $20-$60, but are mostly in the $25 +/- $5 range.

Thanks for the assistance gents. This is exactly what i was hoping for and provides more some really useful lines of inquiry to progress.

suggestions, I will definitely work through them as it's not a bad thing to ensure all contacts are clean and dry in any event.

wpc691 - thanks for the website. Will check it out along with your suggestions. All very worthwhile doing as preventative maintenance irrespective of this issue.

Pete Meisinger - The starter is actually reasonably new. Replaced it a couple of years back. That said, still worth a crack as part of the process of elimination.

Lepke - this sounds most likely based on my observations and intermittent nature of the issue. Is the starting solenoid connected to the starter motor? As mentioned above, the starter is not that old. Would that have come with the new starter? Sorry for the questions - I'll go and do some more research and may be able to answer my own question/s.

gkesden - cheers for that. You give me some hope that this won't turn into something overly expensive. The genset runs beautifully other than this issue so hopefully you are right and it's a cheap fix.

Thanks again gents, I've got more homework now

Ryan

Check me on all of this. I only spent about 3 minutes on it...

Take a look at the service manual, it sort of points to relay K4:
https://www.seapowermarine.com/seapowerwp/wp-content/uploads/2018/05/MDKBH-Service-Manual.pdf

From the parts manual:
http://www.gemo-online.de/pdf/onan/MDKBH_parts.pdf

I think that is part: 307−1617
....which is less than $40.00

On ebay, new:
https://www.ebay.com/p/Onan-Cummins-307-1617-RV-Generator-Starter-Solenoid-Relay-NOS/1428660887

https://www.ebay.com/p/307-1617-Onan-12v-Relay-Solenoid-Start/2115170344

From some other random supplier:

https://www.jackssmallengines.com/jacks-parts-lookup/part/onan/3071617

gkesden said:

Check me on all of this. I only spent about 3 minutes on it...

Take a look at the service manual, it sort of points to relay K4:
https://www.seapowermarine.com/seapowerwp/wp-content/uploads/2018/05/MDKBH-Service-Manual.pdf

From the parts manual:
http://www.gemo-online.de/pdf/onan/MDKBH_parts.pdf

I think that is part: 307−1617
....which is less than $40.00

On ebay, new:
https://www.ebay.com/p/Onan-Cummins-307-1617-RV-Generator-Starter-Solenoid-Relay-NOS/1428660887

https://www.ebay.com/p/307-1617-Onan-12v-Relay-Solenoid-Start/2115170344

From some other random supplier:

https://www.jackssmallengines.com/jacks-parts-lookup/part/onan/3071617

Click to expand...

Thanks gkesden, coincidently I just got off the phone to my local Onan supplier and we discussed the K4 relay as a 1st option. I can source it for around $30 and he has stock so I it seems like an obvious starting point to at least eliminate that as a causal factor. The issue with the solenoid option is Onan don't have it as a separate item. The starter and solenoid are a combined entity and I'm unsure of the complexities associated in disassembling for a relative novice like me. Only one way to learn I suppose.

My plan is to swap out the K4 relay, check all relevant connections etc to the starter (already done once) and see if the problem persists. If the issue remains I'll have to rip the starter out and attempt the disassembly to see if I can locate, remove and replace the solenoid as described.

Thanks again,

Ryan

I havent looked at the engine workshop manual for whatever motor is powering that or the rebuild manual for that starter.

But, it is possible that starter has no built-in solenoid. Some of the smaller ones don't. The suspect "relay" could be it.

Post after checking connections and swapping the relay. If that doesnt fix it, I'll try to find details on that starter.

I'd do it now...

...but I really think it is the relay.

Good luck! Let us know how it goes.

gkesden said:

I havent looked at the engine workshop manual for whatever motor is powering that or the rebuild manual for that starter.

But, it is possible that starter has no built-in solenoid. Some of the smaller ones don't. The suspect "relay" could be it.

Post after checking connections and swapping the relay. If that doesnt fix it, I'll try to find details on that starter.

I'd do it now...

...but I really think it is the relay.

Good luck! Let us know how it goes.

Click to expand...

Thanks gkesden, I hope you are right considering the usual cost of repairs in the marine world. I wish I could do it right now but I'm stuck in the office. Damn work get's in the way of everything.

I will definitely report back as I go.

Ryan

UPDATE

Spent a few hours today removing the sound shield, cleaning and checking all connections for appropriate tightness and connectivity. Replaced K3 and K4 relays. Whilst everything was open I also swapped out the impeller which was close to due. Replaced some of the tired heat shielding and put everything back together.

Ran the genset to operating temp a few times with nil signs of the issue arising. Also ran it under varying loads to emulate normal use. Again, couldn't replicate the problem.

Planning on heading out for a 4 day weekend next weekend so will have to wait and see if the issue rears it's head again but so far, so good. This is the challenge with intermittent issues.

Thanks for all the assistance to date. Time will tell if this episode is complete.

Ryan

UPDATE

Ok - spent a long weekend on the boat running the genset in the usual manner which is generally shorts stints morning and afternoon. No signs of the above mentioned issue re-emerging so far. The genset started and ran perfectly on each occasion. I don't want to call it resolved just yet but so far so good. Don't know if it was the new relays or cleaning and re tightening all connections but either way, so far so good.

Thanks again for all the input and assistance on this.

Ryan