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Oil pressure

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mkirsch

05-11-2008 18:10:35




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What would cause the oil pressure on an engine to start out with the needle straight up the middle, then slowly drop down to nearly nothing as the tractor is worked?

This is on a Cub, BTW.




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Janicholson

05-12-2008 14:14:14




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 Re: Oil pressure in reply to mkirsch, 05-11-2008 18:10:35  
change the oil first!!!!



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Steven f/AZ

05-12-2008 12:48:46




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 Re: Oil pressure in reply to mkirsch, 05-11-2008 18:10:35  
First, put a REAL, numbered gauge on it and see what you actual pressure is. General rule of thumb is 10psi per 1000 rpm. So if your Cub manages 15 to 20 psi hot, you're fine.

The comment about an engine not holding 60 psi all day is wrong - oil pressure has NOTHING to do with how the seals of an engine perform. Seals are not under pressure at all. My H will hold 75 psi at full throttle all day with 5w-40 oil in it, drops down to 50 psi at idle when hot. The pressure relief valve on H's and M's, etc. is set for 75 psi. I'm not sure what the relief valve is set for on a Cub.

Again, if you have 15 to 20 psi at full throttle, you are fine. At idle, you don't need any oil pressure - just volume, so as little as 2 or 3 psi at idle is fine.

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georgeky

05-12-2008 10:22:32




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 Re: Oil pressure in reply to mkirsch, 05-11-2008 18:10:35  
I wouldn't get to fired up about an overhaul yet. Lots of Farmalls do that very same thing. I run 5 or 6 here, and they all drop off quite a bit after running to operating temps, and orking hard. A couple of them even have brand new rebuilds on them. Gauges will also vary quite a bit sometimes. I would hook another gauge to it, and see what that shows. I ran my 1949 C for 21 years, and it never held over 5-7 PSI when working hard. Would show 45 or better cold, but went right on down with heat. I could pull the valve cover, and oil was flying everywhere, so I know it was oiling plenty.

There is a lot of deception to oil pressure gauges to start with. I hear people say mine holds 60 or 70 pounds all the time. It would blow every seal in the engine out if that was true. Had a wise old IH mechanic tell me a hundred times that if it is holding 7 pounds that is plenty. Now I know I will be flogged for this, but most the time it isn't a big deal. You should however make sure you are getting oil where it needs to go, and go from there.

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Lee in Iowa

05-12-2008 05:55:59




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 Re: Oil pressure in reply to mkirsch, 05-11-2008 18:10:35  
My 560 diesel has the same problem. It has almost new rod and main bearings and when the problem showed up I replaced the oil pump and it made no difference. Everybody I've talked to says cam bearings probably need replaced. Anybody know if this can be done without pulling the motor? Lee



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mkirsch

05-12-2008 06:54:44




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 Re: Oil pressure in reply to Lee in Iowa, 05-12-2008 05:55:59  
Lee, I'd have to make an educated guess that you'll need to pull the engine to get at them. I believe they need to be pressed out.

Anybody know what could be done about the cam "non-bearings" on a Cub if the holes are worn? Can they be bored out and a real bearing pressed in? Is it normally not a problem?

Drat, this engine has 110+PSI compression right across the board, and I finally have it running like it should be.

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Rootsy

05-12-2008 07:41:37




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 Re: Oil pressure in reply to mkirsch, 05-12-2008 06:54:44  
My Super A does the same thing... with 15-40... starts out middle of gauge... once she is worked and oil is up to temp needle is just above the red... Makes no noise internally but it'll probably get an overhaul come winter...



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Allan In NE

05-12-2008 04:26:36




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 Re: Oil pressure in reply to mkirsch, 05-11-2008 18:10:35  
I respectfully submit that the "heavy oil/light oil" theory only works at the parade.

Any engine bought up to working metal temp will have the same oil consistency no matter the oil used: about the same as water.

Your engine needs an overhaul.

Allan



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mkirsch

05-12-2008 05:33:55




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 Re: Oil pressure in reply to Allan In NE, 05-12-2008 04:26:36  
I was afraid of that...

Looks like I'm going to have to get me some plastigage and pull the oil pan. Maybe I can put in some oversize rod bearings to get me through the summer. Heck, Dad did that to the M almost 30 years ago now, and hasn't touched it since.



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Allan In NE

05-12-2008 05:44:03




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 Re: Oil pressure in reply to mkirsch, 05-12-2008 05:33:55  
Yeah,

The Red Shop tells me that ANY IH motor should have the bearings replaced at least every 5,000 hours. Gas or diesel.

I've never ran one that long, so don't know. :>)

Allan



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El Toro

05-12-2008 03:55:00




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 Re: Oil pressure in reply to mkirsch, 05-11-2008 18:10:35  
I would try 30 wt oil and see if that helps. You may may need to check your rod and main bearings for wear. Those Cub engines don't have cam bearings and the block bore may be worn where the cam rides. Hal



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ihc49

05-11-2008 21:29:32




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 Re: Oil pressure in reply to mkirsch, 05-11-2008 18:10:35  
camshaft brgs first on the list.



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georgeky

05-12-2008 10:26:57




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 Re: Oil pressure in reply to ihc49, 05-11-2008 21:29:32  
No camshaft bearings in a Cub. Cam rides directly in the bore.



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Andrew Z

05-11-2008 18:19:52




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 Re: Oil pressure in reply to mkirsch, 05-11-2008 18:10:35  
Worn bearings on the rods and mains. and or oil pump is worn. If your running a light oil such as 10w-30 then try strait 40 or `15w -40 that will get you a few pounds there, but this would only be a band aid though. There real easy to work though and parts are relatively cheap.

Andrew



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Janicholson

05-11-2008 18:15:58




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 Re: Oil pressure in reply to mkirsch, 05-11-2008 18:10:35  
Two things easy. thin oil, and heat.
if temp is good, 15 40 oil can make more pressure.

if hot, fix the cooling system.

the cubs's oil pump is built into the block, and is not friendly to get to. worn bearings, or a scored / worn pump are also possible. Good luck, JimN



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