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8N oil pressure


 
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labman98
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Joined: 30 May 2008
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PostPosted: Sat Sep 22, 2012 5:25 pm    Post subject: 8N oil pressure Reply to specific post Reply with quote

Looking thru the many previous threads on this subject I have not found an "fix" so I am going to ask this question again and hope to get some sort of answer. Just finished putting an 8n back together and went to start it and at start get 20-25psi and once it warms up goes down to 5ish. I added new rod bearings, main bearings, sleeves, pistons, rings, but nothing with the oil pump itself. Mains have .002 clearnace, rods have .004. Rods are a little high but still within max allowance (.005) I dropped the pan this morning and took the oil pump out. The gears are a little pitted but not to bad. The shaft and bushing are tight and measure to spec. One thing I cannot find a spec on is the gear to removable plate clearance. There is some wear on this plate and I will clean that up before it goes back together. Is there a spec for this? Or gaskets to adjust this clearnace? I have seen this on cars and it helps greatly to tighten this up with thinner gaskets. Any ideas on where else to look?

Thanks in advance.
 
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old
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Location: Lake of the Ozarks area of MO

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PostPosted: Sat Sep 22, 2012 5:29 pm    Post subject: Re: 8N oil pressure Reply to specific post Reply with quote

Year ago I had an 8N that had low oil pressure and found the oil pump gear plate that has the pick up was ruff. I used a flat surface to lay some sand paper on and sanded out the starches and the oil pressure came right up. Also the pressure relief valve could be set to lot or the spring could be weak which would also cause that problem
 
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JCinKY
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Location: Glendale KY

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PostPosted: Sat Sep 22, 2012 5:36 pm    Post subject: Re: 8N oil pressure Reply to specific post Reply with quote

Lab...my 50 8n is the same way. 25 cold, 8 hot. I rebuilt mine with bearing, rings valve job AND rebuilt the oil pump. My "cap" was scored as well. Sand out any grooves with emory on a piece of glass to stay flat.

Oil pump should have a gasket. I set end play by installing drive gear until too tight to turn by hand then back off until free. Housing could be worn, pressure relief spring too loose (easy fix, stretch or I bought new). You can also lose OP in the cam. Check cam bore in block and cam journals to nominal.

My crank plastigaged to 003 on rods and mains. Looking for a cam, don't want to bore and install bushings.

Oh yeah...galley plugs in? 5lbs not terrible will run a long time on low OP. Just don't idle all day.

Post back -Jeff
 
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Jerry/MT
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Joined: 22 Jul 2003
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Location: Western Montana

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PostPosted: Sat Sep 22, 2012 6:59 pm    Post subject: Re: 8N oil pressure Reply to specific post Reply with quote

Check the relief valve. Make sure it isn"t stuck open or has a weak spring.
 
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CharnerL
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PostPosted: Sat Sep 22, 2012 7:44 pm    Post subject: Re: 8N oil pressure Reply to specific post Reply with quote

If you still have the pan off, check the pick-up tube. The least hole, pin hole will cause severe drop in pressure. I air pressure test each one and find that about every other one had an air leak at the head of the tube.
 
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TheOldHokie
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Location: Myersville, MD

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PostPosted: Sun Sep 23, 2012 4:31 am    Post subject: Re: 8N oil pressure Reply to specific post Reply with quote

labman98 wrote:
(quoted from post at 21:25:19 09/22/12) Looking thru the many previous threads on this subject I have not found an "fix" so I am going to ask this question again and hope to get some sort of answer. Just finished putting an 8n back together and went to start it and at start get 20-25psi and once it warms up goes down to 5ish. I added new rod bearings, main bearings, sleeves, pistons, rings, but nothing with the oil pump itself. Mains have .002 clearnace, rods have .004. Rods are a little high but still within max allowance (.005) I dropped the pan this morning and took the oil pump out. The gears are a little pitted but not to bad. The shaft and bushing are tight and measure to spec. One thing I cannot find a spec on is the gear to removable plate clearance. There is some wear on this plate and I will clean that up before it goes back together. Is there a spec for this? Or gaskets to adjust this clearnace? I have seen this on cars and it helps greatly to tighten this up with thinner gaskets. Any ideas on where else to look?

Thanks in advance.


Ideally end clearance on the oil pump gears should be .002-.003. Gear lash should be max of .003-.004. There should be zero pitting or visible wear on the gears. If you have visible scoring or wear on the pump cover or gears it needs to be corrected.

At .004 your rod bearing clearances are getting pretty sloppy and will undoubtedly have an adverse effect on oil pressure. Did you check camshaft journal clearances or just hope fior the best?

Remember - the wear limit is the absolute maximum acceptable clearance and well beyond what you want new. A rebuild that starts out at or near the wear limit isn't going to perform "like new" or last very long.

TOH
 
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