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An Onan JB Performance Question


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  #211  
Old 09-13-2017, 10:45:22 PM
len k len k is offline
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Default Re: An Onan JB Performance Question

Skiming manuals in past, locked rotor test looks like just to see that starter can make enough torque. Detecting loose armature is just a side benefit.

Can see how with poor factory quality control a thermal or force shrink fit might be too loose. But seems a stretch to believe it can start engine when cold, then slip when a little warmer . Suspect Onan bought their starters pre-assembled from other companies.

I'm still thinking solenoid

Last edited by len k; 09-14-2017 at 01:12:34 AM.
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  #212  
Old 09-14-2017, 11:17:20 AM
len k len k is offline
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Default Re: An Onan JB Performance Question

I'm thinking with ~ 11 V at solenoid, the wiring and control box components are good. But very easy test for them while hot is: Short small solenoid terminal directly to fat bat bolt on solenoid. Using copper rod/bar would be best, but easiest to use a large screwdriver, with insulated handle( possible inductive back voltage ). Don't hold gen frame, that completes the circuit.

Likely will be good spark (100amp solenoid), keep it tight and don't lose your nerve. Safety glasses and long sleeves will help you feel safe.

Last edited by len k; 09-14-2017 at 04:38:16 PM.
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  #213  
Old 09-14-2017, 04:44:05 PM
Leon N. Leon N. is offline
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Default Re: An Onan JB Performance Question

I have some bad news! Things just got worse. I disconnected the gas supply so that the JB would not start. I was conducting len K's test. that is, measured the voltage from the solenoid shifter case to the battery ground terminal. Was surprised to see between 0.25 and 0.5 volts! Gonna make sure the repair shop knows this.

Then to my surprise the starter would not stop cranking the flywheel. I tried the spring loaded start stop switch to no avail, I forced the centrifugal switch closed once again to no avail. In the meantime the pinion disengaged and the starter whined on and on until I detached the positive terminal at the battery. Holey Cow! Must have taken me a good minute to shut down the starter.

Next, disconnected the start/stop switch and checked it out with an ohm meter Checked OK so I reinstalled the start/stop switch. Come to think of it if the centrifugal switch did not shut down the starter, then that spring loaded start/stop switch was not the problem.

So next I tried reattaching the battery positive cable and nearly got knocked on my A as the starter tried to start. So I stopped that effort but noticed my trickle charge was pegged at 5 amperes! Next I measured the voltage at the small terminal on the shifter solenoid and read zero volts. Rats.

I suspect the shifter solenoid main contacts are stuck (welded?) closed. So tomorrow I will remove the starter and off to the repair shop. I do want the old shifter because I think len K is correct. Looks that solenoid failed.
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  #214  
Old 09-14-2017, 05:31:54 PM
Wayne 440 Wayne 440 is offline
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Default Re: An Onan JB Performance Question

Leon, you have more tolerance and patience than I do. If that were my set, I would have put a Mitsubishi starter on it after the first failure of the "rebuilt" unit.
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  #215  
Old 09-14-2017, 06:05:10 PM
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Default Re: An Onan JB Performance Question

Quote:
Originally Posted by Leon N. View Post
I have some bad news! Things just got worse. I disconnected the gas supply so that the JB would not start. I was conducting len K's test. that is, measured the voltage from the solenoid shifter case to the battery ground terminal. Was surprised to see between 0.25 and 0.5 volts! Gonna make sure the repair shop knows this.

Then to my surprise the starter would not stop cranking the flywheel. I tried the spring loaded start stop switch to no avail, I forced the centrifugal switch closed once again to no avail. In the meantime the pinion disengaged and the starter whined on and on until I detached the positive terminal at the battery. Holey Cow! Must have taken me a good minute to shut down the starter.

Next, disconnected the start/stop switch and checked it out with an ohm meter Checked OK so I reinstalled the start/stop switch. Come to think of it if the centrifugal switch did not shut down the starter, then that spring loaded start/stop switch was not the problem.

So next I tried reattaching the battery positive cable and nearly got knocked on my A as the starter tried to start. So I stopped that effort but noticed my trickle charge was pegged at 5 amperes! Next I measured the voltage at the small terminal on the shifter solenoid and read zero volts. Rats.

I suspect the shifter solenoid main contacts are stuck (welded?) closed. So tomorrow I will remove the starter and off to the repair shop. I do want the old shifter because I think len K is correct. Looks that solenoid failed.
You know Leon, For a guy that said you are "80 something" years old, my hat is off to you! You have "Old School" TENACITY some of which I hope to still have in 15-20 years... Just turned 65!
I'll bet you were Hell on wheels in your younger years...And I say that with respect.
I DO agree with Wayne440. JUNK that Dinosaur Prestolite starter and replace it with a Mitsubishi. If you really wanted to save the Prestolite starter, Make a TROPHY base for it and bolt it on to the trophy base and put it on your fireplace mantle.
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  #216  
Old 09-14-2017, 06:31:04 PM
len k len k is offline
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Default Re: An Onan JB Performance Question

Your doing well Leon, I'm ~ 60 and slowing down.

.25 to .5 V solenoid case to ground is not too bad, case is steel and steel is ~ 8X resistance of copper. At 100 amps .5V is ~ .005 ohm.

With solinoid jamming when given a good power source with low source resistance I would look for bad control box connections and wiring. Sounds like some higher resistance limited current in past. Common practice to test solenoid with a shorting screwdriver.

Guessing solenoid jammed. Would be interesting to open up solenoid. Maybe: rust, broken parts, copper bolt head with 1/8 " missing from arc erosion , ect. Copper washer contact is copper plated steel, on old ones copper is gone from arc errosion.

One of those switches that mount on bat terminal might not be a bad idea, also good if short and smoke. For my 7NHM I "temporarily" salvaged jumper cables and clamps from junk jumpstart bat pack. I just clamp them on lead bat post adapter, bites in well. Likely will be permanent

For quick disconnect of bat I use water pump pliers (long handle adjustable pliers.) Side post bats unscrew fast.

Likely starter motor didn't over heat. DC motors with no-load rev up and make more back EMF, reduces current. Schematic shows starter field and armature are in series on my JB spec AA, likely yours too.

Last edited by len k; 09-14-2017 at 08:14:04 PM.
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  #217  
Old 09-14-2017, 07:32:14 PM
Leon N. Leon N. is offline
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Default Re: An Onan JB Performance Question

I am hoping this is the last and only major fix for my JB. I may be wrong but I suspect that starter solenoid shifter was of inferior quality. Will know when I get the old one back. I do not want to introduce non genuine Onan parts if I can help it. The original one lasted for 41 years, this one only 6 years.

I will query again but I did not get a good answer as to where and who the auto-electric shop is purchasing these solenoids. Obviously not from Onan.

Re len K's comment: "I would look for bad control box connections and wiring". I think the control box connections are OK. With the battery disconnected I noticed a few amperes flowing from the battery charger into the JB. That current was flowing from the JB B+ side directly into the positive terminal on the solenoid and thus through the starter to ground.

Note, my JB battery float charger is connected into the control box to a Pair of + and - terminals,

Yes , this is a pain to do because I have to remove the muffler, unbolt the two 4 x 4's, remove the front shroud and thermostatic shutters, then hoist the JB 6 inches, swing it 90 degrees to gain access to the starter. I am down on all fours and just quit for the night.

Checked the pinion to ring gear clearance and attached a picture best I can do. Looks like just about 3/16 inch clearance. Onan says max should be 1/8 inch. No shims were employed with my starter so I suspect this aspect is OK.
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  #218  
Old 09-14-2017, 07:40:58 PM
len k len k is offline
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Default Re: An Onan JB Performance Question

Quote:
Originally Posted by Leon N. View Post
I will query again but I did not get a good answer as to where and who the auto-electric shop is purchasing these solenoids. Obviously not from Onan.
Likely from ~ cheapest supplier he can find.

Few years ago for dad's 87 Chevy Caprice 305 V8 a starter shop said it would be ~$100 for rebuild. Because shop guy was ~ retired and we sent him a lot of business in past he told us that Advanced Auto Parts has starters for ~ $35 and a ~ $45-50 one came with ~ lifetime warentee. $50 one worked fine till we sold car several years later. Shop guy buys them and sells as rebuilt ( doesn't claim HE rebuilt it)

Last edited by len k; 09-14-2017 at 08:08:02 PM.
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  #219  
Old 09-14-2017, 08:04:23 PM
RETCPO RETCPO is offline
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Default Re: An Onan JB Performance Question

"Looks like just about 3/16 inch clearance. Onan says max should be 1/8 inch. No shims were employed with my starter so I suspect this aspect is OK."

IF 1/8 is MAX and you are measuring 3/16 you are over the MAX by 1/16
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  #220  
Old 09-14-2017, 08:18:19 PM
len k len k is offline
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Default Re: An Onan JB Performance Question

Easy enough to get some scrap steel , cut it up and drill some holes for a shim. $3 metal cutting abrasive disk on a carpenter's skill saw cuts steel real fast and easy, Home Depot.

Or car parts store for generic shims, might find something close enough.
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