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Discussion Starter · #1 ·
My JD 316 engine stooped running, took it to a local shop. 1,000 and ten weeks I took it back in parts. Cam shaft broke. I have since repaired and got it to start and oil pressure light came on, replaced sensor still light on. put on a gauge only 5 lbs. where can one find a good oil pump or rebuild kit. I was unable to find a new one. thanks
 

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Welcome to the forum. You may get lucky on Ebay or Amazon. There is a lad or two on the site here that I'm sure can offer some concrete advise and help with finding parts.
 

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Discussion Starter · #3 ·
I have not had good luck on those sites for used parts that can't be tested. they always have a good story but after I put them in they usually fail. Would like to find a rebuild kit if possible or a used part from a honest dealer. It is a lot of work to put in and if it is bad I am wasting my time. But that may be my only out. Thanks
 

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Onan part # for an oil pump is 120-0491, new they are close to $200 now. Before I spent that kind of money, I would make sure the bypass valve is actually seating by inspecting the bypass valve seat and bore for a burr or groove and throw a new bypass valve and spring in it. I've seen many an Onan with low oil pressure because the bypass valve was stuck open from debris in the oil, or scratches in the valve bore.....

120-0398 oil pump bypass valve $10
120-0140 Oil pump bypass Spring $8
120-0491K Oil Pump Rebuild Kit $50


Onan Oil Pump Rebuild Kit

Used Onan Oil Pump
 

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Discussion Starter · #5 ·
are these parts available? I can't find them, but then I am new to this age engine.. I got the spring out but is there a secret to getting the valve out? thanks
 

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Discussion Starter · #6 ·
Onan part # for an oil pump is 120-0491, new they are close to $200 now. Before I spent that kind of money, I would make sure the bypass valve is actually seating by inspecting the bypass valve seat and bore for a burr or groove and throw a new bypass valve and spring in it. I've seen many an Onan with low oil pressure because the bypass valve was stuck open from debris in the oil, or scratches in the valve bore.....

120-0398 oil pump bypass valve $10
120-0140 Oil pump bypass Spring $8
120-0491K Oil Pump Rebuild Kit $50


Onan Oil Pump Rebuild Kit

Used Onan Oil Pump
Thanks for the part #s. Posted on the wrong place but are any of these parts available? I got the spring out but can't get the valve out. Is there secret to do this. I am 78 and my hands don't work so good, thats why I took it to a shop. And they were worthless.
 

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That first link is to onanparts.com, they have every thing you need. Usually the bypass valve comes out with just a magnet, sounds like a pretty good sign it's stuck. Try blowing shop air through the oil pressure switch port. By-pass valve spring bias should allow the valve to unseat and begin to open at 20 psi, and normal oil pressure is 30 psi. If you can't get it to move with a burst of shop air, it's probably stuck. If it was stuck closed, oil pressure would go higher than 30 psi. If it's stuck open, or the bias spring can't completely seat the tip, that's when you get low oil pressure. Gear to pump case clearance, checked with a feeler gauge, is a minimum of .002 -- max of .005.... If the gear to pump case is around .003-.004, you don't need new/used oil pump, and it's another strong sign the by-pass valve is the problem.

A lot of people are surprised to hear that Onan engines are supposed to run either straight 50w, or 20w50 any time it's above 80 degrees.... Page 6-1 in the Service Manual attached below.....

B Series Onan Service Manual
 

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Discussion Starter · #8 ·
I got the valve out . It may have been upside down. These guys were in way over their heads. They had the flat end down and the small end up. was that wrong?
 

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I got the valve out . It may have been upside down. These guys were in way over their heads. They had the flat end down and the small end up. was that wrong?
It works like a carb float needle small end goes down.... Probably going to have oil pressure now
 

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Discussion Starter · #10 ·
It works like a carb float needle small end goes down.... Probably going to have oil pressure now
Thanks so very much for all your help. I will be away for a few days but when I get back will start putting it back together and keep you up to date on my progress.
 

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I got to thinking about it and just checked a B43 I have on the self...... The flat end does go down, the small end is what centers the spring, so it was installed correctly. Make sure the seat for the flat end is in good condition with no gouges, or wear marks that would keep it from sealing. It may have got dinged up by debris when the cam broke. Clean the valve bore up to the point where the valve will slide up and down smoothly. That bias spring is what actually controls the oil pressure, so the valve has to easily slide in the bore. If I recall correctly, the "free length" spec on that bias spring is exactly 1" (25.4mm) to give 30 psi oil pressure.
 

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Discussion Starter · #12 ·
I got to thinking about it and just checked a B43 I have on the self...... The flat end does go down, the small end is what centers the spring, so it was installed correctly. Make sure the seat for the flat end is in good condition with no gouges, or wear marks that would keep it from sealing. It may have got dinged up by debris when the cam broke. Clean the valve bore up to the point where the valve will slide up and down smoothly. That bias spring is what actually controls the oil pressure, so the valve has to easily slide in the bore. If I recall correctly, the "free length" spec on that bias spring is exactly 1" (25.4mm) to give 30 psi oil pressure.
Got it back together. Runs fine oil pressure is good. Now to clean up the wiring, they had cut a lot off wires for some reason.. put on all the tin , change oil and staart cutting grass. Thanks again
 

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Got it back together. Runs fine oil pressure is good. Now to clean up the wiring, they had cut a lot off wires for some reason.. put on all the tin , change oil and staart cutting grass. Thanks again
Those old Onan engines are solid as a rock, only downside now days is what you ran into. Hard to find somebody that knows how to work on them and parts are getting pricey. Glad to hear you got it going....
 
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