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Topic: Onan 6.5 NHM Generator- now a little more complex question (Read 937 times) previous topic - next topic

Onan 6.5 NHM Generator- now a little more complex question

1994 U240

I have determined that I cannot remove the back plug with the gen in place.  (With great effort, I could nearly touch the plug boot with two fingers.)  So it will come out.

I plan to fab a wheeled cart, the same height of the generator mount, with metal strips to serve as slides, so I can unbolt the gen and pull it out onto the cart, without battling gravity.

The problem:  Last trip, the gen worked fine, but at times I would get a whiff of propane.  Now, it starts in 7-8 seconds, and runs very rough, and stops after about 30 seconds.  Yesterday, it ran fine until I added a load, and then it slowed and stopped. 

Have I mentioned that it started twice on its own?  I don't think it is supposed to do that.  I think that was a bit of corrosion in the on-gen starting switch.  I cycled the switch a bunch of times, and have not had the problem since.

I have done some homework (thanks for the manual), and know the shutting off after 30 seconds is proper, when it does not reach proper RPM.  While running, I disconnected the front plug wire and the gen stopped immediately.  I disconnected the rear wire, and it made no change.

I am thinking a fouled plug - does this happen often on an LP generator?

Other possible sources?:  I figure the controller board either works or does not, the coil works on both cylinders or not at all (electronic ignition).  Compression loss could cause the prob, but not likely while it was sitting.  Looks like a plug - do you think?  I plan to remove clean the gen, replace the bay insulation, clean the regulator, replace the plugs, check the plug wires, and look for bad wiring connections.  I will look to see if it is vapor or liquid feed, and maybe convert if it is warranted.

Anything else I should do while it is out?

Has anyone installed a port in the coach floor for access to the rear plug?  I haven't looked, but I'll bet the furnace will be right on top!  Is the drawer slide standard?  I am thinking access for maintenance would be better without the slides and with the extra 1.5 inches of space above the gen.

Share your thoughts with the (relative) newbie!

oldMattB
Matt B
1998 u-320

Re: Onan 6.5 NHM Generator- now a little more complex question

Reply #1 –
Matt, I think it is just as likely to be a plug wire as the plug. I can't imagine a fouled plug on a propane engine unless the rings or a valve is bad.
The selected media item is not currently available.Kent Speers
Locust Grove, OK
1993 U300 SSE 40' (Restored at FOT 2009) Build 4323
720 watts Solar
6V92TA DDEC Silver Engine
2014 Subaru Outback

Re: Onan 6.5 NHM Generator- now a little more complex question

Reply #2 –
That makes sense.  The front plug looked great - just a little tan-white covering, but no heavy deposits or erosion.

Having said that, I bought a Ford truck once with about 150,000 miles on it with a miss problem.  Turned out the plug on the passenger rear, the one nearly impossible to get to, had never been replaced.  It took me about 20 minutes to replace that one plug.  I figure a couple of times, mechanics tried to get to it and gave up, and left the old plug in.

Maybe the rear plug on the generator is 1994 issue!

oldMattB
Matt B
1998 u-320

Re: Onan 6.5 NHM Generator- now a little more complex question

Reply #3 –
Always a bummer when you can't get at a plug. You might need just the right extension, etc. so you can get at it. That said, my number one suspect with the symptoms you describe would be the plug. Plug wire would be number two. So you must be thinking, shall I replace the wire first since it's easier to get to? If the plug looks ok, you might want to try a compression gauge with a flexible hose on it. Someone with the same generator on the forum must have pulled the plug before with the same clearance issue. If you get too tired, take a break and come back to try it later. Easy to cramp if in an awkward position for too long. How about some forum support for this particular issue?
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: Onan 6.5 NHM Generator- now a little more complex question

Reply #4 –
Quote from: Pierce & Gaylie Stewart –
Always a bummer when you can't get at a plug. You might need just the right extension, etc. so you can get at it. That said, my number one suspect with the symptoms you describe would be the plug. Plug wire would be number two. So you must be thinking, shall I replace the wire first since it's easier to get to? If the plug looks ok, you might want to try a compression gauge with a flexible hose on it. Someone with the same generator on the forum must have pulled the plug before with the same clearance issue. If you get too tired, take a break and come back to try it later. Easy to cramp if in an awkward position for too long. How about some forum support for this particular issue?

Thanks for the encouragement, but I still need to replace the bay insulation.  With the insulation removed (read: fallen off in a slimy, greasy mess), there is about an inch between the gen and the top of the bay.

oldMattB
Matt B
1998 u-320

Re: Onan 6.5 NHM Generator- now a little more complex question

Reply #5 –
I still have some new Accuride (clones) glides I used when I built my house. Most are 20" with a couple of 22" inchers, ball bearing, really smooth and will take a medium heavy load like a air cooled generator. They could be used with a tray to make a custom slide out for a generator with an access problem. A lot like the cabinet drawer glides on GVs, only will handle more weight. A pair free with only postage needed. Email for photo.
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: Onan 6.5 NHM Generator- now a little more complex question

Reply #6 –
Same generator here.  Mine ran great but began kicking open the transfer switch on load up.  Cummins blamed old A/C units demonstrated to be pulling excessive amps.  Replaced good A/C with very little improvement.  Always started up instantly though.  Then one day wouldn't start at all.  Back to Cummins.  Replaced electronic ignition and no more transfer switch crapola.  However, it doesn't start easily and I usually am about to give up when it fires up.  Runs horrible for a short time then smooths out and performs great.  Don't know what to think.
Dwayne Keith
1992 U240
3116/MD3060

Re: Onan 6.5 NHM Generator- now a little more complex question

Reply #7 –
When I took possession of my coach, the generator had been running rough. When I got it home I searched online and found the cause could be a plugged vent hose for the propane regulator. It's routed down out the floor, and sure enough found it plugged with dirt. Rolled the end of the hose around in my fingers, the dirt fell out, and the issue resolved. Ran like a champ after that. Same issues though - insulation all but gone, and I wanted to service the gennie properly as I had no records. Had to come out for that.

It was a battle getting it out. Someone had cut two holes in the floor, but they were for accessing the frame attachment bolts. We ended up using a rented engine hoist to get it out of the bay. Could not get any leverage trying any other way. Made a cart out of 2X4s with some leftover wheels and set it on that to service it.

Piugs, filters, parts and service manuals I got from the online Cummins Onan store (the manuals are invaluable resources). The long plug wire had been rubbing on the engine block where it was routed, and the insulation was just about worn through. Went hunting elsewhere for plug wires and gaskets - was surprised by the crazy prices I found.

I ended up buying a pair of Mallory high performance replacement spark plug wires from Summit Racing for $12.95 each (vs $45 for the pair from a Cummins dealer), and a sheet of intake gasket material for $8 (vs $38 for Cummins gaskets) and cut out my own, using the originals as a pattern. The plug wires come with terminal and boots - you need to cut them to length, strip and crimp them. The holes in the floor have been patched, and the gennie is being put on slides for future servicing.

Hope this helps some.
Steve
1991 U225 Grand Villa

Re: Onan 6.5 NHM Generator- now a little more complex question

Reply #8 –
Quote from: Merle Hench –
I ended up buying a pair of Mallory high performance replacement spark plug wires from Summit Racing for $12.95 each (vs $45 for the pair from a Cummins dealer), and a sheet of intake gasket material for $8 (vs $38 for Cummins gaskets) and cut out my own, using the originals as a pattern. The plug wires come with terminal and boots - you need to cut them to length, strip and crimp them. The holes in the floor have been patched, and the gennie is being put on slides for future servicing.

Hope this helps some.
Steve
??  Are you using the same Cummins Onan Store I am??  I paided $16.84 for the one cable and $5.58 for the other.  In fact my whole order for oil filter, air cleaner, fuel filter, 2 spark plugs and the spark plug wires came to a grand total of $65.70 plus shipping and tax which took it up another $20.00.  I know I could have done better, but this order was a hurry up deal at the time.
1994 U225
build #4514

Re: Onan 6.5 NHM Generator- now a little more complex question

Reply #9 –
PatC, The price listed for the Onan parts are in order per my Cummins/Onan Price Book on the spark plug wires.
#167-1602 & 167-1615-01, Not sure about the $20.00 for ups, Sounds a Little high.  We provide many Onan/Cummins Parts and ship world wide. We always use the list prices, we do not  add 10% or more as we have heard from many.
Always nice to have parts that fit.
If your going to the trouble to pull the genset out, it would be good to go over the other items that need attention that can not be accessed when it is in a bad location.
GENERATOR SERVICE COMPANY
Cheers

Re: Onan 6.5 NHM Generator- now a little more complex question

Reply #10 –
I'll remember that, thanks Dave.  Did not know you had a internet store!
1994 U225
build #4514

Re: Onan 6.5 NHM Generator- now a little more complex question

Reply #11 –
Was quoted $28.92 each for plug wires today.  I like to do business locally when I can, but in this case, local is nearly two hours away, and ...

@Dave, email sent to business for parts info
@ Rest of you - thanks for information.  Plan is to do plugs, wires, hopefully clean LP regulator on gen, and see if it is better.  I am really thinking the torn-up plug wire mentioned above might be my problem.  Makes a lot of sense.

oldMattB
Matt B
1998 u-320

Re: Onan 6.5 NHM Generator- now a little more complex question

Reply #12 –
Matt,

When rebuilding the on-generator propane regulator, make sure to use the special high temp gasket set-- made of silicone I believe.  Not difficult to rebuild, but do need the proper gasket kit.


This info is a couple of years old, but here is what was used: Overhaul propane regulator imco RKJ-2 kit 201017 kit.

Brett
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020
 

Re: Onan 6.5 NHM Generator- now a little more complex question

Reply #13 –
@ Brett  Saw your good advice elsewhere on the forums.  Thanks for the part number.

Matt
Matt B
1998 u-320