Onan MDL4 Grinds at Startup

[pmurphy]

My 1987 20kw Onan (32V) generator occasionally "grinds" when the starter tries to engage. I of course stop trying to start it immediately then try again. Most times it then fires off fine. The original starter (32V) was replaced by the prior owner with a 24V starter since I understand the 32V starters are no longer available. I can't image the grinding is a "normal occurrence" when a 24V starter is used but I had to ask. What steps do you think I should take to diagnose and correct the situation? Thanks,
Pat

 

[SKYCHENEY]

Pull the starter and look at the flywheel. The flywheel gear is probably ground down from the starter not meshing with it correctly. It will only get worse and that ring gear is no longer available. You will most likely be replacing that generator with a new one soon.

I had this same issue years ago and after much work, time, and money wasted, I ended up replacing the whole generator. Good luck.

 

[pmurphy]

Sky-
Do you think the grinding may be happening because the 32V feed is causing the 24V starter to spin up faster than it should? If so, I have a 24V power source (inverter bank) that I might be able to utilize to power the starter???? I don't know it that's even possible but it's an idea.

 

[Captain Ralph]

Or, the solenoid is not getting complete engage voltage??

 

[Bob Quinn]

My 1987 20kw Onan (32V) generator occasionally "grinds" when the starter tries to engage. I of course stop trying to start it immediately then try again. Most times it then fires off fine. The original starter (32V) was replaced by the prior owner with a 24V starter since I understand the 32V starters are no longer available. I can't image the grinding is a "normal occurrence" when a 24V starter is used but I had to ask. What steps do you think I should take to diagnose and correct the situation? Thanks,
Pat

If you find the flywheel ground down like Sky said, you might be able to have a gear shop weld and re-cut it. I would think the starter gear would go first though.

 

[whoover]

The ring gear is starting to wear and will eventually fail to engage with the starter bendix at all as Sky mentioned. I had an automotive starter shop replace my bendix gear om my MDJE and it help alot. I have also read of having the ring gear removed and turned over to expose the sharper side of the gear teeth. This will buy you some time if the generator is reliable but it is an Onan and a lot of other replacement parts are almost impossible to find.

Walt Hoover

 

[Bob Quinn]

Sky-
Do you think the grinding may be happening because the 32V feed is causing the 24V starter to spin up faster than it should? If so, I have a 24V power source (inverter bank) that I might be able to utilize to power the starter???? I don't know it that's even possible but it's an idea.

32v power into a 24v would definitely make it spin faster, and over current the starter.
I personally don't think that would make it grind, I'm guessing teeth are worn out like sky said.
Or the throw mechanism is shot, i.e. not pushing the started gear in place properly. Not a mechanic, just thoughts.

 

[Captain Ralph]

Found this in my notes;

191-1550 Used on MDL3, MDL4 and MDL6 (Mitsubishi) 24 Volt DC

191-1604 Used on MDL4 (32Volt DC) (Prestollte – Not Illustrated) (Note-Starter is labeled 24 Volt but is adequate for 32 Volt systems. )

Would your work order offer the part number used? The wrong starter may not engage correctly.

I am concerned that the change in load wattage (starter) may be trying to draw more current (Amps) thru an undersized 32V cable.

Restrictions in current may restrict the starter from engaging with that first (needed) rush of current.

 

[jim rosenthal]

I don't think the increased current would make the starter grind, either, but I'm wondering if increasing the size of the cable from the solenoid to the starter might be advisable, since from what I gather he is running 32 vdc into a 24vdc starter?


I like the idea of turning the ring gear over. The reputation of Onan for parts availability is so dismal that I can't understand how they stay in business. I guess they sell a lot of OEM units. I can't recall ever hearing about someone with an older boat who bought a replacement Onan, but there must be someone out there.

 

[Freestyle]

I had the same generator with the same 24v alternator and the same grinding sound until it ultimately would not engage and start in 2010. I blew about $3,500 trying to repair on the east coast en route to the Bahamas. The generator died in the Bahamas and I replaced it in Dania on the way home to Tampa with n Onan 23 KW unit. I think the total bill was $17k and the new unit has worked flawlessly for 13 years and 5,000 hours. The new unit is also significantly quieter and uses far less fuel.

So milk the generator as it grinds to a halt while shopping for a good deal on a new one. It's a big ticket item that can be had for a lot less than retail if you shop around the boat shows.

Bruce

Freestyle
1985 62 CPMY (54MY with ext)
Tampa

 

[ageless]

I have the same gen and have the same issue. My issue existed with the 32v starter which was replaced with a high torque 24v. As everyone has said, “it’s the flywheel teeth”, I can see the 4-5 that are slightly worn. About every 5th attempt to start it will catch that spot, anticipate it will happen, keep start attempts short, I’m not sure flipping the wheel will help, the weak teeth will still be there. Riding this out as long as possible

 

[SKYCHENEY]

I do think putting 32v to that 24v starter is where the problem starts. The starter winds up faster than it engages. So its already spinning before it comes out all the way to fully engage the ring gear. If had it do it all over again, I would have found a 24v source to feed that starter.

 

[pmurphy]

I do think putting 32v to that 24v starter is where the problem starts. The starter winds up faster than it engages. So its already spinning before it comes out all the way to fully engage the ring gear. If had it do it all over again, I would have found a 24v source to feed that starter.

So I have a 24V inverter bank very close to the generator. How difficult do you think it would be to wire it up so that the starter is getting 24V? Is it as simple as attaching 24V to the starter or are there other things feeding off the starter (other components of the generator) that need 32V? Of course I'd run the risk of running down the inverter bank then not having enough juice to crank the generator, but that's a different issue.

 

[SKYCHENEY]

So I have a 24V inverter bank very close to the generator. How difficult do you think it would be to wire it up so that the starter is getting 24V? Is it as simple as attaching 24V to the starter or are there other things feeding off the starter (other components of the generator) that need 32V? Of course I'd run the risk of running down the inverter bank then not having enough juice to crank the generator, but that's a different issue.

You're going to want to run the controls on 32v. The coil to the start solenoid will be 32v but the load will be 24v. So the small wires 32v, big wires 24v on that solenoid.

 

[pmurphy]

So I pulled the starter today to take a look at the condition of the ring gear on the flywheel and the bendix gear on the starter. The bendix gear was in perfect condition. I'd say that there were two spot on the ring gear, representing about 10% of the entire flywheel, that has been ground down a bit. Now I'm wondering if the 24V starter is the main problem.

 

[ageless]

My 32v did this, the replacement 24v hasn’t furthered the damage or caused any new

 

[pmurphy]

So I've come to learn some things in this journey that I thought I'd share. I don't know if they are true or not, but I'm fairly confident they are. First, since the beginning of time for the Onan 32V generators, they ALL had 24V starters. I had heard that once, then yesterday when I went to a local starter repair shop, the veteran owner told me the same thing without me asking. He took one look at the starter and knew immediately that it came off an Onan. When I told him I was thinking about running a dedicated 24V circuit to the starter he shared with me that they were all always 24V.
The second thing I've come to learn is that the starter will contact the flywheel in one of several spots each time it is engaged. It's something to do with how the engine settles each time when it is shut off. So the starter will only engage in 3 or 4 different spots on the flywheel. That's bad news because much of my flywheel is in good shape but the starter may never try to start in those locations.
I don't know if there is a way to reposition the ring gear on the flywheel or shift the flywheel on the drive shaft a short distance but if so that would then put the starter engaging on a clean part of the ring gear. Just a crazy thought.
Back to my situation, the starter shop thought my bendix shaft had a little wobble in it. They are going to fix that and check over the starter. Perhaps that will improve the situation.

 

[Avenger]

The second thing I've come to learn is that the starter will contact the flywheel in one of several spots each time it is engaged. It's something to do with how the engine settles each time when it is shut off. So the starter will only engage in 3 or 4 different spots on the flywheel. That's bad news because much of my flywheel is in good shape but the starter may never try to start in those locations.

It has something to do with compression. The engine will always stop on a compression stroke. Since the pistons move in pairs there will only be two places on a four-cylinder that it will stop since one or the other of the pair will be on compression.

The good news, is that the ring gear is probably replaceable. If you can't get a replacement, you may be able to remove and reposition the ring gear to a spot with good teeth.

 

[Captain Ralph]

The good news, is that the ring gear is probably replaceable. If you can't get a replacement, you may be able to remove and reposition the ring gear to a spot with good teeth.

Splitting the gen-set in half to get to the flywheel to do this,, is near half the work of total removal in prep of installing a new gen-set.

I do wish pmurphy the best of luck in getting his gen-set running again.
I do not mean to type out negative comments here. Just maybe a reminder that working on that Christmas list earlier this year could be a thought.

Sadly, the MD4 dinosaur that everybody keeps up on life support, has near run out of parts and factory support.
IMO, pmurphy 's gen-set will be running soon but I'm afraid still on borrowed time.


But as many have learned already, Northern lights makes a great 16 or 20KW replacement. Once the checkbook recovers, all sleep better with that one worry or concern gone.
NL sets are still on 3 month + waiting list in most areas.

 

[pmurphy]

Splitting the gen-set in half to get to the flywheel to do this,, is near half the work of total removal in prep of installing a new gen-set.

I do wish pmurphy the best of luck in getting his gen-set running again.
I do not mean to type out negative comments here. Just maybe a reminder that working on that Christmas list earlier this year could be a thought.

Sadly, the MD4 dinosaur that everybody keeps up on life support, has near run out of parts and factory support.
IMO, pmurphy 's gen-set will be running soon but I'm afraid still on borrowed time.


But as many have learned already, Northern lights makes a great 16 or 20KW replacement. Once the checkbook recovers, all sleep better with that one worry or concern gone.
NL sets are still on 3 month + waiting list in most areas.

Ralph-
You are right on the money. A new gen in is my future. I just hope to get through with this summer's Bahamas adventure on the one I have now......