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Onan Generators

What Have You Done to Your Onan Generator Today?


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  #1621  
Old 04-23-2015, 06:33:04 PM
len k len k is offline
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Default Re: What have you done to your Onan generator today?

We never bothered cutting mica on starters, never notice they needed it. Just sanded them with ~ #500 sandpaper, #360 first if needed it. We did body work and just had a lot of these 2 grits handy.

Difference between starters and other motors might be starters MAY have less inductance to cause arcing at the brushes. I say less inductance because from what I remember there are less turns because winding wire is so MUCH thicker in starters than general purpose motors. Just my guess.
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  #1622  
Old 04-24-2015, 06:46:12 PM
Leon N. Leon N. is offline
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Default Re: What have you done to your Onan generator today?

I would like to purchase a replacement point set (Onan P/N 160A2) and the companion condenser (312A116). Any suggestion where I could obtain these two items for my JB?

Leon
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  #1623  
Old 04-24-2015, 07:23:32 PM
gnucklehead gnucklehead is offline
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Default Re: What have you done to your Onan generator today?

I think those numbers convert to Onan 160-0002 and 312-0116. Onanparts has the points (they seem to be pretty common, around $15), but not the condenser. Does it really need to have the tab on the end, for mounting? Saw a condenser on the big auction site for $22 . I can never seem to find all the parts I need from the same vendor.
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  #1624  
Old 04-24-2015, 09:09:08 PM
Leon N. Leon N. is offline
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Default Re: What have you done to your Onan generator today?

Well I had to shut down my JB today due to improper operation which has gotten so bad that I had no choice but to tear into it. The problem was a random back firing through the carburetor. After running under 2/3 load, 22 amperes per leg, for about 20 minutes it started random back firing to the extent that the frequency would drop to 57 Hz then recover for a few minutes and then repeat over and over again. No problem running at NL.

So not having ever done a tune up since 1970 and accumulated about 1500 hours or so, I had no choice but to investigate. What I found out was the timing advanced a bit too much and the points were severely pitted to the extent they would not make a clean break at 5 degrees ATC. But they would break twice. Once near TDC and then at about 3 degrees ATC. I use an ohm meter and set the timing with the JB stopped per 967-500.

So I re installed the original points which were much less pitted and they seem to make a clean break at 5 degrees ATC. And I intend for now to install the original condenser. I also replaced the two Champion H8 spark plugs which were worn to about a 0.035" gap.

My intention is to reinstall the sheet metal and see if it operates a bit better. If it does, then I will tackle the control box which needs a clean up due to a mice infestations back some 20 years ago. In the meantime I am on a search for the replacement points and condenser. I appreciate hearing anyone else has run into the problem I just described.
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  #1625  
Old 04-24-2015, 09:33:19 PM
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Jim McIntyre Jim McIntyre is offline
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Default Re: What have you done to your Onan generator today?

For gas fuel, shouldn't that be 5 BTC?

Do you have a timing light? I wonder how you know your ignition advance is working to spec. I'd want to confirm 35 BTC once the engine is up to speed.

Still, a new condensor and point set seems like a good step. Last you reported this, I thought it was mixture-related?
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  #1626  
Old 04-24-2015, 10:02:17 PM
Leon N. Leon N. is offline
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Default Re: What have you done to your Onan generator today?

Jim Thank you for pointing this out. Geeze in my haste, I was following the instructions on page 29, Figure 34 in 967-500. Fortunately, I have not re installed the sheet metal and I can re adjust to 5 degrees BTC. I cannot find my timing light. May have to purchase another one. That TC mark is not very clear on my flywheel There are three yellow stripes on my flywheel. I believe one is 25 BTC, the other two are closer together. I believe on is TC and the third one not too far away is 5 ATC?. I do not want to remove the cylinder head to confirm the TC point. Will have to take a second look. I know I set the timing correctly way back when. Something has changed and I suspect is was the timing. It would run under heavy load vey nicely for about 20 minutes and then things start to go down hill.

Yes, I could fire up the machine briefly to check the timing advance once I get a timing light. Thank you again for pointing this out!
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Old 04-24-2015, 10:11:41 PM
nothingbutdarts nothingbutdarts is offline
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Default Re: What have you done to your Onan generator today?

Quote:
Originally Posted by Leon N. View Post
I do not want to remove the cylinder head to confirm the TC point.
Really all I do is pull the plugs, get a long plastic tie and hold it in the cylinder while turning the engine over by hand, till it pushes the tie up as high as it will go and that should get you close enough to find the TDC mark.
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  #1628  
Old 04-24-2015, 10:36:17 PM
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Default Re: What have you done to your Onan generator today?

Leon, Not 100% sure about your set, but on my JBs, the timing marks are much much easier to see once you take off the blower sheet metal housing. Mine are all stamped with 0, 25, and 35. The paint marks are there too, but the flywheel stampings are the gold-standard...
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  #1629  
Old 04-24-2015, 11:43:46 PM
Ray Lynch Ray Lynch is offline
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Default Re: What have you done to your Onan generator today?

From the Master Service Manual Rev.9-76, page 14-2:
"The flywheels on Onan J series gasoline and gaseous fuel engines are stamped at TC and 10, 25 and 35 BTC positions at the factory. A jig fixture is used to locate the markings exactly. White paint marks are also added along with the stampings at the TC and 25 positions for gasoline engine timing while yellow paint marks are added at the 10 and 35 positions for gaseous fuel engine timing.
On Vacu-flo engines the TC and other timing marks are offset from normal position 95 deg and a dot button hole is used for viewing the timing marks and pointer ".

Wonder why they didn't mark for 5 deg BTC and 5 deg ATC as well?
Ray
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  #1630  
Old 04-25-2015, 09:43:30 AM
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Jim McIntyre Jim McIntyre is offline
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Default Re: What have you done to your Onan generator today?

Quote:
Originally Posted by Ray Lynch View Post

Wonder why they didn't mark for 5 deg BTC and 5 deg ATC as well?
My guess is that sets like Leon's have a 'manual' hand start provision. Newer ones don't. In order for hand crank starting to be safe, the timing needed to be retarded, so Leon's set has a centrifugal advance mechanism, which was eliminated later. With that gone, there was no need for the +5 and -5 marks anymore...

Or maybe Onan decided that 0 and 10 were better for manual hand crank starting than +/-5 (because now that I think about it, I don't know what else the 0 and 10 marks would be for)

Last edited by Jim McIntyre; 04-25-2015 at 09:58:40 AM.
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