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  #51  
Old 05-23-2017, 11:55 PM
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Oak Oak is offline
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Did some more digging today.

Boomer, on the Green site is telling me that the bypass starts opening at 20 psi so I guess these don't build much more pressure than that.

Before he posted that info I decided to pull the oil bypass spring and check it. It is in spec, length wise at 1". I pulled another spring from a used block I have and it was also 1". I then figured I would stretch it a little and see what happens. I stretched it to about 1.2" and reinstalled it. Here is how it ran after that.
https://www.youtube.com/watch?v=F7UE...ature=youtu.be

That looks a lot better.

I ran it for maybe 5 minutes and look what happens to my pressure.
https://www.youtube.com/watch?v=qGrKzZlg_Ws

I'm not sure if the spring got weakened and I didn't pull it to check because I have a new spring coming from Onan this week.

It looks like to me that the pump can't pump enough oil at slow idle or I have an issue with an internal leak or a clearance is too large somewhere but I would think you could hear that and would it loose that much pressure? Did the 30W oil get warm and caused the pressure to drop off?

Anyone have any thoughts on this issue????? I know, I know, I shoulda repowered but that's not going to happen.
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  #52  
Old 05-24-2017, 01:25 AM
J-Mech J-Mech is offline
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Todd,

I've been digging on this for an hour. I have yet to find a lube circuit diagram for that motor. Of coarse, in a Kohler manual, they have it. Not Onan apparently.


So, here is what I can tell you. Good rule of thumb for oil pressure is 10 PSI for every 1000 RPM. So, you should get around 5-10 PSI at idle, and 30 or so WOT. Yours looks a little low. Being that you pulled the spring apart a bit and it got better, I'd say your spring is shot. It likely lost pressure after running due to working out that assembly lube and also because the oil warmed up. I'd say replace the spring and see what happens.

FWIW, I NEVER overhaul a motor without installing a new oil pump. Can't live without oil pressure.

On your comment about a loose tolerance causing low pressure. Yes, it's possible. I'd be looking at the main and cam bearings, but they are all new. No way to check clearance on them though. So, hopefully the clearance was correct. I didn't take time to refresh myself on this rebuild, but were the main journals on the crank ground? Did you check the max wear limit on the cam journals that ride on the bearings? Both would be places for oil pressure loss. And no.... if something was loose, you likely wouldn't hear it. We're not talking about being able to rattle around, we're talking low tolerance. .0015" under spec on either the crank of cam and it could have low pressure, but it wouldn't rattle or anything.

Replace the spring and see where that gets you.
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  #53  
Old 05-24-2017, 08:32 AM
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The important thing is, it is getting oil under pressure.
Without a gauge you would not know and wouldn't worry.
A little loss in the bearings on the crank mains/rods also cam bearings,
and a little loss in the possible worn pump, adds up to what you are seeing.
I'd not worry, I don't see anything that concerns me on that gauge.
Remember, a lot of engines are splash lubricated.
It will prolly out last what it is powering!
You have been in it, so you know for sure what it looks like in there.
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  #54  
Old 05-24-2017, 09:30 AM
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Todd,
I talked to a friend of mine that works on Onan generators. He said back when they rebuilt the P series they always put in a new oil pump. You can use this information as you see fit..
It sure sounds good, can't beat the sound of a twin exhaust Onan.
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  #55  
Old 05-24-2017, 10:36 AM
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Thanks guys for looking into this issue I'm having. It is bugging the crap out of me.

Jonathan, from what I can tell by looking at one of my blocks the oil pressure pickup for my gauge is on the entering side of the relief vale. From what Boomer is telling me, that spring starts dumping oil back into the timing cover case at 20psi.

The oil that is not dumped into the case enters the flywheel side main bearing at the 1:00 position. The crank is drilled to feed oil to the rod journal and the oil that is left leaves the main bearing at the 11:00 position to feed the flywheel side cam bearing.

Back in the block before the relief valve, the passage is drilled to feed the crossover pipe to the pto side of the engine. A lot of times this pipe will get crushed if the engine throws a rod but I checked it and flushed it with brake cleaner and compressed air when it came back from the machine shop. Here is what it looks like. The area that looks crushed is for clearance of the rod.
DSCN2078.jpg
The crossover pipe feeds oil into the bearing cap on the pto side. Here you can see the oil passage at the 7:00 position on the cap.
DSCN2046.jpg
This feeds the oil to the pto side main bearing and the crank is drilled to feed the rod journal. The cam bearing on the pto side is not pressure lubed. The rely on oil "walking up the cam" to lubricate it.(can you believe that?)

That is about as good as I can describe it.

New oil pump...they don't exist and are NLA. I'll pull one apart and get some pics. They look to be built well but I guess they can wear. No plastic junk here.
DSCN2052.jpg DSCN2037.jpg

The crank was ground .10 under and new main bearings were installed. The cam was not ground but had new bearings installed.

George, I'm fine with 20 psi max but at low idle it scares me when it drops to what looks like 0 on my gauge. I'm thinking that is why a lot of these machines twist off the pto end rods from lack of oil traveling to that side of the engine.

Terry, they sure do have a sound of their own.

I would like to thank you guys for taking the time on this issue I'm having. Maybe if someone is foolish enough to rebuild one in the future this will help them.
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  #56  
Old 05-24-2017, 10:38 AM
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Quote:
Originally Posted by Oak View Post
Cad, I agree. I put it on to because 982's don't have anything for loss of oil pressure. I'm not sure what my other 982 runs at because it is stock. I've posted on different forums, watched a ton of YouTube vids and I hear a lot of guys are running 30 to 50psi IIRC. I think Wheel Horse uses a switch to kill the ignition if it drops to 5 psi. I ordered a new spring tonight so I'll change it and hope the issue goes away but I'm thinking it is something else.
We were just talking about adding a gauge to my 982 this past Sat. since there is not even a light. The Onan service manual seems very vague, never references a light or a gauge.
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  #57  
Old 05-24-2017, 11:29 AM
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Why would they only want 20 psi of oil pressure and why not 30 to 50? Is too much bad for the bearings or hard on the pump?
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  #58  
Old 05-24-2017, 11:47 AM
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It's not hard on the bearings, but that little oil pump may not be made for extended pressure.

If your new spring doesn’t fix it and it were mine, I'd find a spring that would at least maintain 5 to 10 psi at idle.

FWIW, your gauge goes to what, 100psi? Can you find a lower pressure gauge?
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  #59  
Old 05-24-2017, 11:51 AM
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Jon, that's good thinking on the gauge. It doesn't make sense to have a 0-100 gauge when it looks like 20 is the max I will see. Let me look and see if I can find one in the 0-30 or 0-40 range.
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