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Onan 7.5JB Centrifugal switch HELP!


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  #1  
Old 10-28-2013, 11:33:19 PM
gov2mod gov2mod is offline
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Default Onan 7.5JB Centrifugal switch HELP!

I've got an Onan 7.5JB 3CR/8388AA generator with battery ignition. It was made in May 1977. When starting it, as it is cranking it tries to start but stops as soon as I let go of the start switch. If, when it's trying to start, I push the points shut on the centrifugal switch it will go ahead and start and will run fine until I shut it off. I understand the points on the centrifugal switch are supposed to shut at 900 rpm but I would guess the engine would already have to be running to reach 900 rpm. Any ideas on why I have this problem? Thanks for any help.
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Old 10-29-2013, 06:47:00 AM
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J. McNugget J. McNugget is offline
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Default Re: Onan 7.5JB Centrifugal switch HELP!

The points are adjustable. I believe the gap is 0.025" but someone will be along to correct that number if it is incorrect. (I'm working by memory as I dash out the door...)

John
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Old 10-29-2013, 07:03:19 AM
Max Thompson Max Thompson is offline
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Default Re: Onan 7.5JB Centrifugal switch HELP!

Quote:
Originally Posted by J. McNugget View Post
The points are adjustable. I believe the gap is 0.025" but someone will be along to correct that number if it is incorrect. (I'm working by memory as I dash out the door...)John
Close: .020. Like the points, be sure the contacts are clean. Has the plate assembly been removed lately, or did this just start out of "the blue"?
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Old 10-29-2013, 07:49:21 AM
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Default Re: Onan 7.5JB Centrifugal switch HELP!

Ran across this before. If you re-adjust point gap, and it works for a while but problem returns, I'd suggest you replace the soft plunger seal and the plunger that operate the point contact. I've had units where cleaning the plunger rod doesn't even help in the long run. Don't know why. But replacing them has always worked.
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Old 10-29-2013, 12:37:48 PM
gov2mod gov2mod is offline
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Default Re: Onan 7.5JB Centrifugal switch HELP!

This is how the generator was when I bought it. The points are adjusted to the correct .020. If I push the points closed while cranking it starts and runs fine. I just what is supposed to pull these points closed so it can start.
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Old 10-29-2013, 07:27:25 PM
Max Thompson Max Thompson is offline
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Default Re: Onan 7.5JB Centrifugal switch HELP!

On the back side of the centrifugal switch plate, there is a counter weight that rotates & causes a “sleeve” to move toward the front of the engine, allowing the nylon plunger that activates the switch to move back into the housing, thus closing the points.

If the nylon plunger is damaged or as Eric mentioned, it sticks, the plunger will not follow the “sleeve” back.

It sounds like you could use a parts manual, so you can see how it is put together. An e-mail address will get you this as well as service manuals if you would like.
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Old 10-29-2013, 07:54:31 PM
gov2mod gov2mod is offline
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Default Re: Onan 7.5JB Centrifugal switch HELP!

It could just be gummed up from sitting for several years, I'll have to look at it. I've got a manual but it shows little of this switch. Email is gov1mod@aol.com Thanks for any help.
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Old 10-29-2013, 08:11:13 PM
Max Thompson Max Thompson is offline
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Default Re: Onan 7.5JB Centrifugal switch HELP!

You should have a box full.
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Old 10-29-2013, 09:31:01 PM
gov2mod gov2mod is offline
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Default Re: Onan 7.5JB Centrifugal switch HELP!

Thanks, I really appreciate it.
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Old 10-30-2013, 06:34:04 PM
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Default Re: Onan 7.5JB Centrifugal switch HELP!

I removed the switch, the diaphram and plunger, all looked great. The rubber was soft and pliable and the plunger didn't look worn or broken.
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