4KY Onan Generators

steven reynolds · 03-06-2022, 11:30 AM

I have 2 4KY generators, 4KY FA26100H, S/N H920480588 has a bad engine, low power, smokes a lot (OHV), 4KY FA26100J, S/N J990001613 no power to fuel pump or ignition, will stay running only if start button is held in. A lot of parts and time has been put into this one. Can the J engine be used to replace the H engine?

Rich Biebel · 03-08-2022, 12:14 PM

Both are old units......going by the serial numbers... 1992 and 1999

I've only changed a couple engines on those but my educated guess is yes you can swap engines...but there could be some sort of mismatch that you'll only find by attempting it.
The Generators rotor attaches to the engines tapered crankshaft stub. It's got a pin on it to index the rotor to the crank and in turn the blower wheel that has the magnet for ignition triggering. Timing is fixed so if anything is not right with that assembly it won't run.....

It will be a complete disassembly of the machine to swap engines.....

Labor cost exceeds the value of the machine from a business standpoint so when an engine is blown or just worn out I trash them or put in a parts pile.....

Old machines had different control boards and voltage regulators but basically were the same as newer machines. No emission devices either on the old ones.....

I have 2 myself but they are much newer....

I would fix the one that is newer. Won't stay running unless rocker switch is held in indicates NO AC output power and the number one thing to check is the brush circuit......If it's open at the F+ and F- wires the brushes are worn out and or the rotor is open......The F+ and F- wires connect to the control board and just need to be ID'ed, disconnected and ohm test that pair.....A good reading is around 30 ohms......If the reading is good the control board or voltage regulator may be bad.

I've fixed many of them, new and old........it takes some time but diagnosis is just a process like anything else. No big mystery....

steven reynolds · 03-08-2022, 11:49 PM

Thanks for the reply and advice, probably will fix the newer one as it has a better engine and also has a new voltage regulator/control board, and other parts on it that are new.

Steve

03-06-2022, 11:30 AM	#1
steven reynolds Junior Member Join Date: Jan 2009 Location: Missouri Posts: 44 Likes: 2,553 Liked 13 Times in 11 Posts	4KY Onan Generators I have 2 4KY generators, 4KY FA26100H, S/N H920480588 has a bad engine, low power, smokes a lot (OHV), 4KY FA26100J, S/N J990001613 no power to fuel pump or ignition, will stay running only if start button is held in. A lot of parts and time has been put into this one. Can the J engine be used to replace the H engine?

03-08-2022, 12:14 PM	#2
Rich Biebel VIP Member Join Date: Jun 2007 Location: Northern New Jersey suburbs Posts: 2,307 Likes: 25 Liked 537 Times in 211 Posts	Re: 4KY Onan Generators Both are old units......going by the serial numbers... 1992 and 1999 I've only changed a couple engines on those but my educated guess is yes you can swap engines...but there could be some sort of mismatch that you'll only find by attempting it. The Generators rotor attaches to the engines tapered crankshaft stub. It's got a pin on it to index the rotor to the crank and in turn the blower wheel that has the magnet for ignition triggering. Timing is fixed so if anything is not right with that assembly it won't run..... It will be a complete disassembly of the machine to swap engines..... Labor cost exceeds the value of the machine from a business standpoint so when an engine is blown or just worn out I trash them or put in a parts pile..... Old machines had different control boards and voltage regulators but basically were the same as newer machines. No emission devices either on the old ones..... I have 2 myself but they are much newer.... I would fix the one that is newer. Won't stay running unless rocker switch is held in indicates NO AC output power and the number one thing to check is the brush circuit......If it's open at the F+ and F- wires the brushes are worn out and or the rotor is open......The F+ and F- wires connect to the control board and just need to be ID'ed, disconnected and ohm test that pair.....A good reading is around 30 ohms......If the reading is good the control board or voltage regulator may be bad. I've fixed many of them, new and old........it takes some time but diagnosis is just a process like anything else. No big mystery.... __________________ Rich Biebel S/C 1479 Stock 147R Last edited by Rich Biebel; 03-08-2022 at 12:21 PM.

03-08-2022, 11:49 PM	#3
steven reynolds Junior Member Join Date: Jan 2009 Location: Missouri Posts: 44 Likes: 2,553 Liked 13 Times in 11 Posts	Re: 4KY Onan Generators Thanks for the reply and advice, probably will fix the newer one as it has a better engine and also has a new voltage regulator/control board, and other parts on it that are new. Steve