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Onan 7.5JB-18R bought off Craigs List


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  #21  
Old 10-12-2015, 10:40:06 AM
ClydeM ClydeM is offline
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Default Re: Onan 7.5JB-18R bought off Craigs List

"The build sheet does not indicate it is high compression so I would look for something in the 100 psi range maybe a bit higher. Before pulling it apart I would try to get it started and put a good load on it for an hour or so , that would loosen it up and give a truer compression reading."

My "Onan Gas and Gasoline Engine Tune -Up Specification" wall poster (dated Sept. 91) lists the JB ( spec A-C) compression with throttle plate and choke open at 120-140 psi. and beginning spec D shows 180-200psi for gaseous fuel. I will try to get this turned into a PDF so it can be shared. It is about 16" X 24" and is not a complete list as it includes the caveat that models not listed (like the CCK) "may be obsolete". It does list most, maybe all of the diesels though.
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  #22  
Old 10-12-2015, 11:43:19 AM
MBB MBB is online now
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Default Re: Onan 7.5JB-18R bought off Craigs List

Quote:
Originally Posted by Max Thompson View Post
I would hesitate to run it more than a few minutes without the sheet metal tins installed. It will not cool properly without them.
Good point Max. I think we all just figure everyone we converse with knows better as we do. Probably could run a fan running full speed at it and it would work fine.
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  #23  
Old 10-12-2015, 02:03:57 PM
b1miller b1miller is offline
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Default Re: Onan 7.5JB-18R bought off Craigs List

I went back and verified that the model and serial number are correct. This generator also came with an Onan Auto Demand Control Box and that box is also setup for 120/240V.

So my questions are:
1. Based on the missing sheetmetal I do not plan on any extended operation until I can replace or fabricate a replacement.
2. Is the automatic temp control shutter assembly shown in the parts manual (p/n 18) essential?
3. It looks like the cylinder air housing cover is also missing.

I plan to keep looking for a donor 7.5JB with the proper sheet metal parts or whatever bits and pieces I can come up with.
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  #24  
Old 10-12-2015, 02:06:40 PM
b1miller b1miller is offline
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Default Re: Onan 7.5JB-18R bought off Craigs List

Ooops, forgot to upload the sheet metal photos
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  #25  
Old 10-12-2015, 02:21:16 PM
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BigBlockChev BigBlockChev is offline
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Default Re: Onan 7.5JB-18R bought off Craigs List

There would be a Lid which attaches to the 4 bolts sticking up and goes around the valve cover, it has a lip pointing down which mates up to the sheetmetal on all sides. there is also a front cover which has the curved corner to go under the lid and mates up with the side and bottom bits, it has a hole for the air cleaner assembly which may be one of several configurations. The rear thermostatic vanes may or may not have been there and in my opinion are not necessary, you would just get full cooling all the time. Maybe useful in a very cold climate. Cheers Dan
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  #26  
Old 10-12-2015, 03:11:37 PM
Leon N. Leon N. is offline
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Default Re: Onan 7.5JB-18R bought off Craigs List

You also need the four unique rubber foot pads for mounting the JB so that is does not walk around. I would not run it without them.
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  #27  
Old 10-12-2015, 04:30:24 PM
b1miller b1miller is offline
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Default Re: Onan 7.5JB-18R bought off Craigs List

It did come with the 4 rubber isolation pads.

Thanks to all for your valuable information.
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