8N low oil pressure

[BigHart]

Hello, not sure if anyone can help.
I have a freshly rebuilt 8N engine with front distributor. Replaced oil pump gears, and oil pressure relief spring and plunger. At start up it has 60+ lb pressure, but when it gets up to operating temp pressure falls to 10lb. Tried different weight oils with same results. Any ideas?

 

[Rusty2N]

10 lbs at idle is not a concern. Does it climb as you increase RPMs? At 4-500 RPM that
motor isn't spinning very fast so neither is the pump.

 

[Den N Ms]

BigHart, You say replaced oil pump gears,but what about the bushings? What was the thickness of the gears?Clarence of the gears to cover plate?

 

[BigHart]

When she is receding up and hot I ve got about 20lb. Pressure.

 

[BigHart]

Had to use the old bushing. Could not size the new one. Don t know what the clearance is between the gears and the housing.

 

[TheOldHokie]

(quoted from post at 17:37:05 05/21/23) Had to use the old bushing. Could not size the new one. Don t know what the clearance is between the gears and the housing.

Whats the hot oil pressure @1500 RPM?

TOH

 

[BigHart]

Ya, I would say receded up its around 1500 rpm. I could put a tach on it.

 

[TheOldHokie]

(quoted from post at 17:35:01 05/21/23) When she is receding up and hot I ve got about 20lb. Pressure.

Thats a bit disappointing on a rebuilt egine but acceptable. What its telling you is some of your oil clearances are still on the high side. Might or might not be in the oil pump.

The best you can reasonably expect is about 30 PSI. Its a flathead so as long as you keep the main/rod bearings filled and have enough pressure to maintain a cylinder wall spray you are good to go.

TOH

This post was edited by TheOldHokie on 05/22/2023 at 05:20 am.

 

[BigHart]

Yes, definitely disappointing. Main and rod bearings should be good. Was not able to replace the cam because I couldn t find a new one for a front mount distributor. The bores were within tolerances, but maybe not good enough. I did covert it to a spin on oil filter. Could that cause a problem? Doesn’t seem likely to me.
Thanks for all your help everyone!

This post was edited by BigHart on 05/22/2023 at 03:45 pm.

 

[wore out]

What parts did you use to convert it to a
spin-on filter? The original filter
canister has a small restrictive orifice
to limit oil flow through the bypass
filter (seems to me 0.030'', others will
know for sure) and if the new filter or
base doesn't have a similar restrictive
orifice WAY too much oil will pass
through the filter and dump into the
governor housing causing a great drop in
engine oil pressure.

 

[BigHart]

I found a kit to convert it on eBay. Maybe not a good idea.
I don t know if there is a bypass hole or not . It is basically an aluminum base with a hole in and a hole out with a place to screw on a filter. Cost me $50.00 lol