Onan 12.5 JC won't crank!

[mike sylvester]

Hey guys, love this forum - lots of info!
gen. 12.5jc-3cr131/7512aa -e760137637- 120/240 @52amps.
Problem, It's been starting fine for two years since i had it, now it just clicks once or twice and then nothing when i throw the start switch? I had the charger on it and tried to start and the charger went from 14v down to 7 - 8volts. had the starter checked and it's OK. When i take the batt. term. off and then reconnect it, it will click, then nothing?? Could it be the selonoid in the control box? If so where could i get one(any part #) Also if anyone would have a parts list for this unit that they could e-mail to me i would be greatfull. (ecwrestoration@yahoo.com) & possible info on this unit.
Much thanks, Mike

Just forgot, where can i get a oil pressure guage (mechanical)for this JC? My guage needle is stuck @ 50 psi? Thanks

[Billy J Shafer]

The solenoid number should be 307-0845. You should by it from Onan. If you get the wrong one it will damage the system. The oil pressure guage you should be able to get at any good parts house.

[Kimbra Dean]

Sounds like a bad battery (Broken post or broken internal connection) or bad battery cable to me.

[Billy J Shafer]

Check the solenoid before you replace it. If it is working you should have good voltage to the starter. Some times the contacts inside burn and will not allow voltage through.

[Tom Marshall Jr.]

Clean the cabels and if it still drops to 7 try another battery.

[mike sylvester]

Battery is new and so are the cables,

[Wayne 440]

If you haven't already, it might be a good idea to temporarily substitute a battery that is known to be up to par. "New" doesn't always mean good, that assumption has cost me a time or two. An old (and somewhat dangerous) troubleshooting method is to run a jumper cable from the battery straight to the starter terminal. If it cranks, the starter and battery can be eliminated.

[mike sylvester]

Tried cranking it with new batt. and charger connected, still one click/buzz and then nothing - untill you take one batt. term off and then you can try starting. But all you get is the same click/buzz?

[EricWood]

Put the voltmeter on the starter input cable again. Sounds like you've pretty much eliminated all else, try cranking--low voltage to starter and "buzzing" would indicate to me your contact disc has burnt up in the start solenoid as Billy mentioned.

eric

[Deneh]

I had this happen to me a couple of times while testing unknown gennies. It was the fact that each of those units would not rotate due to being siezed. Did you try to bar the unit over to see if the engine turns freely?

[mike sylvester]

engine was running fine 2 dats ago.

[Raymond]

You didn't say where you tested the voltage. If it drops to 7 V across the battery terminals (posts), then either the battery can't supply the current (needs at least 550 CCA above ~55 deg, 750 CCA ~32Deg.) or the starter is bad. Run a current test on the battery. I watched my fasther spent 2 weeks and $250 on his boat that wouldn't start with a new battery, I put the battery out of my car in it and it spun like a new one. If the battery posts stay at 10 or above but the voltage across the starter solenoid is less, there is a bad connection which should show up as a voltage across the tested segement. Check bat+, to sol. +, then sol. + to starter lead +, then starter case to battery negative post. There's a drop somewhere and it should get real hot real fast unless the starter is bad. What kind of test proved the starter good? A no load bench test won't prove anything accept maybe a good solenoid. If the start relay is chattering causing the starter solenoid to bump you may have a bad ground in the control box. It's a braided strap on the back side that connects to the generator frame, and carries the negative or ground current for all the relays and the start (K11) (not the starter) solenoid.

[Dave Edmonds]

If you don't have one, purchase an inexpensive digital voltmeter (Harbor Freight has them for $5.00 or less, Lowes and Home Depot have them for somewhat more, but still inexpensive). You don't need a really high quality meter unless you need it for a living (like I do - I use a Fluke digital, plus an old Simpson 260 analog meter, when the digital "lies" to me because of transients, etc.). As was mentioned above, you're losing voltage somewhere - either it's not there in the first place, or something (like a bad starter or a bad solenoid) is "stealing" it.
Dave Edmonds

[Richard L]

I dont have the mannual here on the boat, but I recall that the starter is controlled by the crank disconnect switch that operates off the cam drive gear,and operates the start disconnect switch.The switch opens when the plant reaches a certin RPM and drops the starter out. There is an adjustment on the switch which is located on the front of the engine,under a tin cap, you will find a set of contact points and need to check if they are clean and gapped correctly. Would like to have more info but my brain is old and all my books are at the house. Can check this weekend.
Rick

[BTPost]

That Switch is called the Centrifugal Switch and is driven off the Governor Shaft from the opposite side of the Governor Gear, and is located just above,
and to the right, the LubeOil Filter, on xDJB/E's and xDJC/F's. It should have two (2) wires going to it. the Gap should be set at .020",and the contacts should be Clean and Dry.

[mike sylvester]

Thanks guys, will check the point gap this weekend. How do you check the selonoid in the control box? Would still like to get my hands on the parts list for this unit if anyone has one. Thanks, mike

[mike sylvester]

Update..... Generator started working again???didn't fix anything, go figure???? Thanks for all the help.

[Billy J Shafer]

Mike us old techs will tell you. If it is working and you don't know why. Just take credit for it and if it stops again. You can tell your friends something else must have gone wrong.