bad oil pressure after rebuild

I have an older 8N that we rebuilt the engine on. Went to rebuild the oil pump, gears were the wrong size. Even got a second set and they didn't fit.
had the bushing replaced and sized. Ended up putting the old gears back in. So we start it up, pressure comes right up to 35psi, but after it gets
warm it is down to 10 or less at idle. We have straight 20 oil in it.
Any suggestions?
 

what was the pressure before the rebuild?

did u replace the mains?

to my way of thinking, straight 20 is thin for summertime. i run 30W in mine.
 
Billfromwisconsin,What were the clearances of the rod and main bearings?Where they at the high end of limits? Block to camshaft clearances if to much the block may have to have bearings installed in it.Oil pump needs to be rebuilt correctly.A 30 weight or 10w40 weight oil might help but won't make up for a bad rebuild.
 
My engine was rebuilt about 15 years ago. With 15-40 oil it runs 35 pounds in 100 degree weather. After working a couple of hours it will drop down to 20 when you idle it all of the way down.

Something is wrong.

Plastiguage all of your bearings to make sure you got the right thing. Also see about that oil pump. It sounds fishy. I hope it works out there so you aren't align boring it.
 
I did a mini rebuild on my late 8N about 9 years ago. Someone in an earlier life had put in a larger set of oil pump gears. Current oil pressure on mine is about 35/40 cold oil and about 20 hot oil. I only use 30 non detergent all year long. An old Ford owners booklet says if your engine has 25 at 1500 RPM it is OK.
 
I had a similar happening, when I had my 1945 2N rebuilt. When I got it back, He said: "The gears were a little bigger, so I had to put extra gaskets in it (DUH). If I remember right, I think there was a change in pump size width of gears from 1/2" to 9/16", in 8N's. Pressure has remained like yours, so I haven't done anything or complained, but if the Pressure drops suddenly, then I know where to check, IMMEDIATELY.
Comments on the above will be understood as "acceptable".
Charles Krammin
 
the bearing clearance was in the middle on both, about .0015. I know we should of done the pump correct, but he said it has good pressure before. The gears came form here, they were to big in diameter, so we called, they sent a second set, same thing. It was a job my friend and me kind of got "dumped" on us. another guy said he would do it, then got in the shop and disappeared.
 
My 52 8-N seemed to me to be low on pressure, always wondered why as it always has impressed me as being tight and in good shape. At idle and warm it is about 15 pounds with 30 grade or 10-30 grade. I changed it to Delo 15-40 a long time ago. 60 lbs cold, running hard and warm around 35, good 20 at idle. Always liked Delo--my 8-N confirms it to me in the performance
 

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