Topics

Onan ballbearing check and valves values

Gary Silver
 

Hi All:  
I inquired of Cummins (Onan) about the specifics of changing the generator bearing.  The original person that helped me sent me copies of the updated (latest and greatest) parts and master service manuals for my 7MDKAL-431 genset (posted them in the files section with May 2020 in the title).  He escalated my request for help to his superiors and they responded but indicated that the service should only be done my a "certified Onan" technician.  After explaining to them that several of us (out of a group of owners having about 800 of their gen-sets) had attempted using a "Onan certified technician"  and the technicians had never done it and didn't want to do it.  I finally prevailed on Onan to give me the procedure after explaining that I am an FAA certified aircraft mechanic and know my way around wrenches.  Here is the reply to my questions that I request be directed to a technician who had actually done the procedure: 
Question 1.  Is the rotor able to be self supported when the end-bell is removed.   Answer:  "The rotor can support itself for a small amount of time. I would not leave it unsupported for more than 60 minutes, but it should be fine to remove the end bell"   This is in line with what Craig said relative to a Northern Lights genset.  
Question 2.  What is the degree of engineered interference fit for the bearing in the counter-bore and on the rotor shaft.  In other words how much difficulty can I expect in removing the end-bell.  The service manual says to “tap” it off.  Is that realistic or can I expect a major struggle. Answer:  "I personally used a 2 jaw puller or if the end bell has threaded holes a steering wheel puller to remove it. The other option is to use 2 pry bars at the outside edges and slowly work it off. It is a fairly tight fit or should be unless the bearing began to turn in the end bell housing  Note: be sure to disconnect F1 and F2 as the exciter stator will come off with the end bell."

Thanks to Onan for stepping up and getting me the info.   Now all I have to do is perform this service.  Hope this is helpful to others. 

Gary S. Silver, M.D. 
sv Liahona
Amel SM 2000 # 335
Boat: Puerto Del Rey Marina, Puerto Rico
Me: Farmington, Utah, USA



 

Craig & Katherine Briggs SN 68 Sangaris Tropic Isle Harbor, FL
 

Hi Oliver,
Yes, that does seem to be a strange statement in the manual to "inspect every 2000h or 5 years". I am at a loss to know what or how you would inspect it, unless perhaps, it was visibly corroded or something like that. 
Sorry but I don't know the spec/size for the bearing on your Onan genset.
Cheers, Craig

Oliver Henrichsen, SV Vela Nautica
 

Hello Craig,

Thanks for your explanation. 

I would also rather tend to change the ball bearing, just wondered because my manual says: inspect every 2000h or 5 years, left me wondering how.?
Anyway I will prepare to change the ball bearing.

My Genset is ONAN MDKBM, 
The ballbearing part no is: 510-0112

Does anybody know the specification / size of this bearing? 

Oliver from Vela Nautica Amel54#39 
Martinique 




On Mon, May 18, 2020, 23:29 Craig & Katherine Briggs SN 68 Sangaris Tropic Isle Harbor, FL via groups.io <sangaris=aol.com@groups.io> wrote:
Hi Gary and Oliver,

Per my earlier post, (to Gary's 2 questions) 1. the rotor is bolted to the flywheel and is self-supporting. The end frame with its bearing is, of course, needed for support when the genset is running.  2. The bearing will slip in an out with only, perhaps, putting the new one in the freezer for awhile before inserting it.

And, Oliver, as to a procedure for checking the generator bearings for wear, I am unaware of a procedure for that and think you really want to replace it after the hours recommended in the manual (if I recall, it's 2500 hours). One really doesn't normally check bearings for wear - it is a preventive maintenance item and you really want to replace them before they wear "too much" and cause damage to other components.

This is not brain surgery - it is a simple DIY task that doesn't need a paid mechanic, unless, of course, that's how you choose to maintain your boat.

Good luck with it,
Craig

Craig & Katherine Briggs SN 68 Sangaris Tropic Isle Harbor, FL
 

Hi Gary and Oliver,

Per my earlier post, (to Gary's 2 questions) 1. the rotor is bolted to the flywheel and is self-supporting. The end frame with its bearing is, of course, needed for support when the genset is running.  2. The bearing will slip in an out with only, perhaps, putting the new one in the freezer for awhile before inserting it.

And, Oliver, as to a procedure for checking the generator bearings for wear, I am unaware of a procedure for that and think you really want to replace it after the hours recommended in the manual (if I recall, it's 2500 hours). One really doesn't normally check bearings for wear - it is a preventive maintenance item and you really want to replace them before they wear "too much" and cause damage to other components.

This is not brain surgery - it is a simple DIY task that doesn't need a paid mechanic, unless, of course, that's how you choose to maintain your boat.

Good luck with it,
Craig

Gary Silver
 

Follow Up on Onan Genset Bearing Replacement.  I contacted Onan thru their web site and received a reply from Jesse Ketive, a 

Cummins Level 1 Diagnosis, representative.  He was most helpful and sent me the latest and greatest service and parts manuals for our Onan genesis.  These I just posted to the files section with the "Current as of May 2020" designation.  Having read the procedure for the generator bearing replacement again several times I have inferred that this isn't such a big job after all.  All the references to supporting the  engine and generator rotor etc etc are relative to complete removal of the generator and rotor from the engine and doesn't apply to our project.  

I have queried Jesse to get me some data from a person in the company who has actually done this and answer two questions:  1.  Is the rotor self supporting without damage when the endbell (i.e. the end frame that has the counterbore into which the bearing seats) is removed? and 2.  How tight of an engineering fit is the bearing in its counterbore and and the engineering fit of the bearing onto the rotor shaft?   The description uses the word "tap" to describe removing the endbell from the rotor so I am hopeful that these are light interference fits and not insurmountable by we owners.    I'll post more when I hear back from Jesse. 


All the best, 

Gary S.  Silver, M.D.
s/v Liahona
Amel SM 2000 # 335  lying Puerto Rico - Puerto Del Rey Marina

Oliver Henrichsen, SV Vela Nautica
 

Hello and thanks 4 your answers.

But the question was:

Is there a procedure to check the generator bearings for wear? As mentioned in the manual / service plan?

Oliver from Vela Nautica Amel54#39 
Martinique 

On Sun, May 17, 2020, 18:41 CW Bill Rouse <brouse@...> wrote:
Sorry, guys. I did exactly the same thing as Gary Silver, and the bearing was never installed.
CW Bill Rouse Amel Owners Yacht School
Address: 720 Winnie, Galveston Island, Texas 77550 
View My Training Calendar


On Sat, May 16, 2020 at 12:45 PM Craig & Katherine Briggs SN 68 Sangaris Tropic Isle Harbor, FL via groups.io <sangaris=aol.com@groups.io> wrote:
Hi Gary,
It's been awhile, but I replaced the rotor bearing on my Northern Lights 6kw genset in situ with little difficulty. The rotor remains bolted to the flywheel as you remove the end with the bearing - no external support needed. I recall I did the old put-it-in-the-freezer trick to shrink the bearing and it slid in with no press needed.  That was at about 3000 hours; now I'm at 7500 and am overdue, so will tackle again soon. (I'm getting a very slight vibration with heavy loads.)
If you want to remove the rotor, as I did because it needed rewinding from salt water corrosion shorting the wires ($176 in La Paz VZ), it's heavy but quite manageable by hand. However it doesn't sound like you'd need to remove it for the 2500 hr. (if I recall correctly) bearing replacement..
Cheers, Craig

 

Sorry, guys. I did exactly the same thing as Gary Silver, and the bearing was never installed.
CW Bill Rouse Amel Owners Yacht School
Address: 720 Winnie, Galveston Island, Texas 77550 
View My Training Calendar


On Sat, May 16, 2020 at 12:45 PM Craig & Katherine Briggs SN 68 Sangaris Tropic Isle Harbor, FL via groups.io <sangaris=aol.com@groups.io> wrote:
Hi Gary,
It's been awhile, but I replaced the rotor bearing on my Northern Lights 6kw genset in situ with little difficulty. The rotor remains bolted to the flywheel as you remove the end with the bearing - no external support needed. I recall I did the old put-it-in-the-freezer trick to shrink the bearing and it slid in with no press needed.  That was at about 3000 hours; now I'm at 7500 and am overdue, so will tackle again soon. (I'm getting a very slight vibration with heavy loads.)
If you want to remove the rotor, as I did because it needed rewinding from salt water corrosion shorting the wires ($176 in La Paz VZ), it's heavy but quite manageable by hand. However it doesn't sound like you'd need to remove it for the 2500 hr. (if I recall correctly) bearing replacement..
Cheers, Craig

Craig & Katherine Briggs SN 68 Sangaris Tropic Isle Harbor, FL
 

Hi Gary,
It's been awhile, but I replaced the rotor bearing on my Northern Lights 6kw genset in situ with little difficulty. The rotor remains bolted to the flywheel as you remove the end with the bearing - no external support needed. I recall I did the old put-it-in-the-freezer trick to shrink the bearing and it slid in with no press needed.  That was at about 3000 hours; now I'm at 7500 and am overdue, so will tackle again soon. (I'm getting a very slight vibration with heavy loads.)
If you want to remove the rotor, as I did because it needed rewinding from salt water corrosion shorting the wires ($176 in La Paz VZ), it's heavy but quite manageable by hand. However it doesn't sound like you'd need to remove it for the 2500 hr. (if I recall correctly) bearing replacement..
Cheers, Craig

Gary Silver
 

Hi Oliver:

I have been concerned about the generator rotor ball bearings for the last 15 years.  As I recall the manual indicates this should be replace every 5?? of years or ?? hours of run time.  In 2006 I purchased the parts and engaged a "Onan Certified" technician in St. Thomas to do that change.  He took the end cover off the generator, looked at the bearing, became completely intimidated with the task and decline to do it, even though I had the new parts available.  I have since had discussion with the technicians at Cummings Diesel (Salt Lake City), the local Onan dealer and where I source my Onan parts.  They don't have any direct experience but did produce for me several pages from their service manual for this model that very vaguely discuss it.  Those instructions don't give a detailed process and seem to imply that the procedure is so rudimentary that one shouldn't need to have to inquire how it is done.  I have tried to puzzle out the process from these resources but have concluded that it would be impractical for me to tackle the job while the unit is "below decks".  As I understand it, the rotor is supported, by a means not specified, while the generator end housing is removed, the bearing extracted from its counter-bore, and a new bearing is pressed into place.   Perhaps there is some sort of tool/support for doing that.  I am guessing the rotor with its windings is very heavy.  I wonder if Bill Rouse might have any sway to get a procedure for this from Onan.

Gary Silver 
s/v Liahona
Amel SM 2000 # 335
currently at home in Utah while my boat languishes in Puerto Rico

Oliver Henrichsen, SV Vela Nautica
 

Hello,

1.
My ONAN manual indicates that the ballbearings need to be checked for their tollerance. In regular maintenance schedule. 

Does anybody hold an instruction how to do that?

2.
What are the valve values for the exhaust valves? 
Onan MDKBM-5754457

Oliver from Vela Nautica Amel54 #39 
Martinique