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Onan 7.5JB Centrifugal Starter Disconnect Switch

Jim McIntyre

Subscriber
Last Subscription Date
07/10/2019
I removed the CS/points assembly from the engine tonight. The CS plunger was in fact sticking in the bore. The plunger has some taper, and the 'fat' end was toward the timing gear, and preventing me from simply pulling the pin out from the outside. Once I had the whole assembly off, I was able to push the plunger in and extract it.

I can't explain why the plunger had taper. The fat end was a tiny bit scored.

It certainly wasn't lack of oil - the design provides plenty of lube to this area, and there was ample oil on it when I inspected it. I popped the plunger in the lathe and 'polished' it with 1000 grit emery paper, reducing the fat diameter down a few thou. It slides easily through the bore now.

I believe the plunger is made of garolite, an epoxy/cloth laminate material, similar to common PCB material (but with cotton instead of fiberglass). Not sure, but that's the way it looks to me. The plunger can't be made of metal because it touches the electrical contact.

I switched to synthetic oil a while ago. I suppose I can't rule out some incompatibility causing the garolite to swell a bit. Other that, I'm at a loss to explain why this just happened out of the blue. I never had a hint of a problem with this CS until now.

Everything else looked good, including the advance mechanism, ignition points plunger, etc.

The most time-consuming part is scraping off the old gasket and cutting a new one. Mine tore pretty badly when I removed the assembly from the engine.

The pics show the taper on the plunger, and the plunger after I polished it up, ready to go back in , as far as I can tell. The end with the groove faces 'out' away from the timing gear. The groove is for the red rubber oil seal.


EXECUTIVE SUMMARY: Plunger was too fat and got stuck in the bore.
 

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JohnnyC

Subscriber
Last Subscription Date
07/13/2019
I removed the CS/points assembly from the engine tonight. The CS plunger was in fact sticking in the bore. The plunger has some taper, and the 'fat' end was toward the timing gear, and preventing me from simply pulling the pin out from the outside. Once I had the whole assembly off, I was able to push the plunger in and extract it.

I can't explain why the plunger had taper. The fat end was a tiny bit scored.

It certainly wasn't lack of oil - the design provides plenty of lube to this area, and there was ample oil on it when I inspected it. I popped the plunger in the lathe and 'polished' it with 1000 grit emery paper, reducing the fat diameter down a few thou. It slides easily through the bore now.

I believe the plunger is made of garolite, an epoxy/cloth laminate material, similar to common PCB material (but with cotton instead of fiberglass). Not sure, but that's the way it looks to me. The plunger can't be made of metal because it touches the electrical contact.

I switched to synthetic oil a while ago. I suppose I can't rule out some incompatibility causing the garolite to swell a bit. Other that, I'm at a loss to explain why this just happened out of the blue. I never had a hint of a problem with this CS until now.

Everything else looked good, including the advance mechanism, ignition points plunger, etc.

The most time-consuming part is scraping off the old gasket and cutting a new one. Mine tore pretty badly when I removed the assembly from the engine.

The pics show the taper on the plunger, and the plunger after I polished it up, ready to go back in , as far as I can tell. The end with the groove faces 'out' away from the timing gear. The groove is for the red rubber oil seal.


EXECUTIVE SUMMARY: Plunger was too fat and got stuck in the bore.
Jim, glad that you found the problem and hopefully a new plunger is available. Check for burrs or anything abnormal in the bore hole where the plunger goes. If all looks good, replace the plunger and slap it together. I think you should be happy that the cause of your problem was not the CS gear mechanism since it may be difficult hunting down a replacement at a reasonable price. Early on I think I mentioned about the gasket as I had the same issue.

JohnnyC
New Jersey
 

Jim McIntyre

Subscriber
Last Subscription Date
07/10/2019
...Early on I think I mentioned about the gasket as I had the same issue...
Ha - yeah you did, but I couldn't figure out any way to remove the assembly without tearing it. It must have been assembled with some sort of adhesive. The bore looks smooth. I think I'll just put the polished plunger back in and run with that...
 

zuhnc

Subscriber
Last Subscription Date
12/08/2019
On your JB, since this mechanism also operates the ignition points, make certain the gear is TIMED properly upon reinstallation. There are marks on the engine gear and the CS gear. zuhnc
 

Motorhead

Subscriber
Age
67
Last Subscription Date
07/09/2019
Jim, Did you check the operation of the weights? I know with centrifugal advance distributors that the advance weights can get sticky.
 

Leon N.

Registered
I removed the CS/points assembly from the engine tonight. The CS plunger was in fact sticking in the bore. The plunger has some taper, and the 'fat' end was toward the timing gear, and preventing me from simply pulling the pin out from the outside. Once I had the whole assembly off, I was able to push the plunger in and extract it.

I can't explain why the plunger had taper. The fat end was a tiny bit scored.

It certainly wasn't lack of oil - the design provides plenty of lube to this area, and there was ample oil on it when I inspected it. I popped the plunger in the lathe and 'polished' it with 1000 grit emery paper, reducing the fat diameter down a few thou. It slides easily through the bore now.

I believe the plunger is made of garolite, an epoxy/cloth laminate material, similar to common PCB material (but with cotton instead of fiberglass). Not sure, but that's the way it looks to me. The plunger can't be made of metal because it touches the electrical contact.

I switched to synthetic oil a while ago. I suppose I can't rule out some incompatibility causing the garolite to swell a bit. Other that, I'm at a loss to explain why this just happened out of the blue. I never had a hint of a problem with this CS until now.

Everything else looked good, including the advance mechanism, ignition points plunger, etc.

The most time-consuming part is scraping off the old gasket and cutting a new one. Mine tore pretty badly when I removed the assembly from the engine.

The pics show the taper on the plunger, and the plunger after I polished it up, ready to go back in , as far as I can tell. The end with the groove faces 'out' away from the timing gear. The groove is for the red rubber oil seal.


EXECUTIVE SUMMARY: Plunger was too fat and got stuck in the bore.
Jim thank you for the quick diagnosis. Garolite I understand is a fiberglass base material that is used in printed circuit boards, according to Google. I hope your problem is not due to a incompatibility problem with synthetic oil? I suppose it could be. I have been using Mobile One synthetic since it first appeared on the market. So far I have not seen a CS problem but a problem with the other plunger, that drives the points.

Thank you for the nice work and sharing.
Leon
 

Jim McIntyre

Subscriber
Last Subscription Date
07/10/2019
On your JB, since this mechanism also operates the ignition points, make certain the gear is TIMED properly upon reinstallation. There are marks on the engine gear and the CS gear. zuhnc
Roger that. Done.

Jim, Did you check the operation of the weights? I know with centrifugal advance distributors that the advance weights can get sticky.
Yep, all good.

... I have been using Mobile One synthetic since it first appeared on the market. So far I have not seen a CS problem but a problem with the other plunger, that drives the points...
I'll take a look at the ignition point plunger tonight to see if I can figure out any way it might get stuck as yours does. I think it's metal though, so not an oil compatibility issue...
 

Jim McIntyre

Subscriber
Last Subscription Date
07/10/2019
Well, it's all back together and seems to be working fine, with the newly 'polished' CS plunger.

One thing I see now is the seal on the CS plunger isn't necessarily 'oil tight' and I think that keeping this area free from excessive oil leakage really means you need to keep the crankcase vent system working as intended. Any crankcase pressure is gonna start a lot of oil leaks here.

Leon, the only cause I can think of for your sticking points plunger is the rubber oil seal.

Thanks all for advice, experience and pictures!
 

Leon N.

Registered
Well, it's all back together and seems to be working fine, with the newly 'polished' CS plunger.

One thing I see now is the seal on the CS plunger isn't necessarily 'oil tight' and I think that keeping this area free from excessive oil leakage really means you need to keep the crankcase vent system working as intended. Any crankcase pressure is gonna start a lot of oil leaks here.

Leon, the only cause I can think of for your sticking points plunger is the rubber oil seal.

Thanks all for advice, experience and pictures!
yes, I noticed some oil pooling in the bottom of the breaker box cover. I was surprised during a routine check some time ago as to why the points condenser was covered in oil. I concluded one or both of the plunger oil seals was leaking so I leave the cover off now. The amount of leakage is inconsequential. What machinery doesn’t leak or ooze some oil over time.

Jim, thank you for the info and advice. And, yes, I suspect my oil breather is not working like before since I do not see any moisture in the carburetor throat for sometime now. It‘s +7 this morning. Later today I intend to fire up the JB after sitting some 6 weeks in the cold. Want to see if my fix for the start/ignition relay cold operation works.
 

Leon N.

Registered
yes, I noticed some oil pooling in the bottom of the breaker box cover. I was surprised during a routine check some time ago as to why the points condenser was covered in oil. I concluded one or both of the plunger oil seals was leaking so I leave the cover off now. The amount of leakage is inconsequential. What machinery doesn’t leak or ooze some oil over time.

Jim, thank you for the info and advice. And, yes, I suspect my oil breather is not working like before since I do not see any moisture in the carburetor throat for sometime now. It‘s +7 this morning. Later today I intend to fire up the JB after sitting some 6 weeks in the cold. Want to see if my fix for the start/ignition relay cold operation works.
Well, I did not get a chance to fire up my JB today because the boss requested I take her to the VA to pick up a prescription and then we went Mall shopping. I will try to get to the JB tomorrow. BTW, that garolite sounds similar to that Westinghouse product called Micarta. Micarta was used in those large HV oil circuit breakers connecting the. pneumatic mechanisms to the switch gear.
 

EICBob

Subscriber
Age
62
Last Subscription Date
07/13/2019
Nice fan Jim....
I have one that looks similar but has brass colored metal blades.

-BobC
 

Leon N.

Registered
Nice fan Jim....
I have one that looks similar but has brass colored metal blades.

-BobC
OK, I fired up the JB this morning. OAT was +15 probably a tad colder in the shed since the low was about +7 yesterday. Anyways it started with after a few spits and skips - I resorted to the hand crank start mode so I could better listen to the plugs firing or not firing and it‘s easier on the starter drive.
Max, I am now convinced I fixed the start,disconnect, ignition relay contacts cold weather problem by cleaning both the NC and the NO contacts on that relay while in place. No longer a pressing need to R&R it at this time. I have all the stuff, mostly thanks to Max to refurb the CB. Geeze I hate to tear into it, but maybe this Summer I will. Start up oil pressure was 50+? Steady state load was 25/31 @240 volts. Will let it run for about 1 & 1/2 hours as the wife drys some clothes.

Can’t say enough about this one fine standby power source! Only you guys can appreciate that fact.
 

EICBob

Subscriber
Age
62
Last Subscription Date
07/13/2019
Can’t say enough about this one fine standby power source! Only you guys can appreciate that fact.
I agree Leon....so far when I have needed mine she has not let me down. Can't wait till I can do a decent permanent install so I don't have to run the huge cord to the house and drag the 100lb tank to the set.

-BobC
 

Leon N.

Registered
I agree Leon....so far when I have needed mine she has not let me down. Can't wait till I can do a decent permanent install so I don't have to run the huge cord to the house and drag the 100lb tank to the set.

-BobC
I am wondering if it would be a good idea to start a new thread with the goal to explain how the old Onan JB control circuits work. I cannot think of many things that could cause a user panic more than to have his JB fail to start during an emergency power outage.

I was thinking about my years of experience with the old JB, you know the one with the hand crank switch, and what can the operator do if, for example, the start switch will not work, or the engine dies when the start switch is released or why will it only run if the hand crank switch is on?

After going through the electrical control circuits, I would think it would be helpful, at least to some guys, to explain in non-technical terms the cause and effect of certain no-start or no-run conditions, pin pointing what specific action the operator could take to get the JB running ASAP. Strictly a non technical discussion since even to me for a long time the Onan JB control wiring diagram was rather confusing.

I would envision this thread to be rather short, focusing on just a few electrical components, and not get bogged down into details. I think it would be very helpful if, for example, JohnnyC could amplify what I would, like to offer with a few pictures of some of the items that would be the focal point.

Is this a good idea or not?
 

Bent Trigger

Subscriber
Last Subscription Date
10/03/2019
Nice! If you start it, they will come!! 😻 Pics are the best way to get close to the problem!!
 

Jim McIntyre

Subscriber
Last Subscription Date
07/10/2019
One potential issue might be the different variants of JB controls over the years. Mine, for example, does not have the hand crank switch. Some sets have LOP shutdown and some don't.
 

Max Thompson

Sponsor
Last Subscription Date
09/03/2019
Not sure we could improve on the "illustrated diagram" contained in the service manual. It shows the starting sequence from start to stop. I think most of the confusion comes from the K-12 double throw relay and the 6-
v coil on it.
 

Leon N.

Registered
Not sure we could improve on the "illustrated diagram" contained in the service manual. It shows the starting sequence from start to stop. I think most of the confusion comes from the K-12 double throw relay and the 6-
v coil on it.
My idea is to speak from my experience with my specific JB. I just want to respond to, for example, the comment, “the JB stops when I release the start switch”. Maybe some folks can extrapolate what I have learned to their machines, I do not want to speculate or talk about variants. I will leave that to others. All I want to do is explain if I can in simple terms what I have determined to be a simple fix to a critical matter than can prevent the JB from operating. I will have to give this some more thought based upon my experiences.
 
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