Oil Pressure Back, some

mwbailey

Member
So, thanks to advice from the Forum, I found an
oil pressure gauge at TSC to check my oil pressure
issue -- pretty good when first started, 0 after
warmed up. I suppose I still have a problem, of
sorts, but with new gauge installed I get 40 psi
at half throttle when cold, drops to 15-20 psi at
half throttle when warm, and about 5 psi at idle.
It"s definitely NOT 0 psi at idle, but it still
isn"t very good. I"ll have to decide whether I
have enough nerve to go through the oil pump or
replace bearings. . . .

Oh, nobody told me that the oil would spurt all
over me when I cranked it up without gauge but
with a dish under the the open end of the line!!!
That was a mixed blessing: good pressure, messy
tractor.
 
(quoted from post at 15:01:04 08/12/14) So, thanks to advice from the Forum, I found an
oil pressure gauge at TSC to check my oil pressure
issue -- pretty good when first started, 0 after
warmed up. I suppose I still have a problem, of
sorts, but with new gauge installed I get 40 psi
at half throttle when cold, drops to 15-20 psi at
half throttle when warm, and about 5 psi at idle.
It"s definitely NOT 0 psi at idle, but it still
isn"t very good. I"ll have to decide whether I
have enough nerve to go through the oil pump or
replace bearings. . . .

Oh, nobody told me that the oil would spurt all
over me when I cranked it up without gauge but
with a dish under the the open end of the line!!!
That was a mixed blessing: good pressure, messy
tractor.

I've heard before from machine shops that the old saying was you need 10lb of oil pressure for every 1,000 rpms. so 5 psi at 450 rpms would be in line with that school of thought
 
(quoted from post at 15:18:47 08/12/14)
(quoted from post at 15:01:04 08/12/14) So, thanks to advice from the Forum, I found an
oil pressure gauge at TSC to check my oil pressure
issue -- pretty good when first started, 0 after
warmed up. I suppose I still have a problem, of
sorts, but with new gauge installed I get 40 psi
at half throttle when cold, drops to 15-20 psi at
half throttle when warm, and about 5 psi at idle.
It"s definitely NOT 0 psi at idle, but it still
isn"t very good. I"ll have to decide whether I
have enough nerve to go through the oil pump or
replace bearings. . . .

Oh, nobody told me that the oil would spurt all
over me when I cranked it up without gauge but
with a dish under the the open end of the line!!!
That was a mixed blessing: good pressure, messy
tractor.

I've heard before from machine shops that the old saying was you need 10lb of oil pressure for every 1,000 rpms. so 5 psi at 450 rpms would be in line with that school of thought

Next time someone tells you that ask them how an old splash lubricated B&S lawn mower engine running at 3600 governed RPM survives with ZERO oil pressure???

My guess is anyone that knows the correct answer to the lawn mower question won't volunteer that "old saying".

TOH
 
(quoted from post at 17:02:54 08/12/14) hard to find them oil caps/fingers on regular tractor rods and caps though.

Yes - you have to have oil to the bearings but my point is that it does not need to be externally pressurized oil.

WRT journal bearings that algorithm is meaningless even on a pressure lubricated engine. A solid 10 PSI at the journal furthest from the pump is probably just as good as 40 PSI on the vast majority of automotive engines. All you need is enough pressure to maintain the oil supply passing through the clearances. More than that does absolutely nothing for the journals.

TOH
 

i agree.. look at some single lung hit/miss engines that the rod has a catch cup onthe crankshaft at the journal and scoops oil as it spins. :)
 
Bailey.......why are you surprized that oil pressure decreases as the oil warms up??? It's called VISCOSITY factor. ALL oil does that. That is why you now have multi-viscosity oil....ie 10-30wt. Remember, when the N-Engine was designed in 1939, it was spec'd for 6-qts of 30wt detergent and recommended a change to 40wt in HOT plowing weather. Surprizingly enuff, 30-40wt multi-viscosity oil does that automagically for you. 40psi when cold means yer oilpump AND crankshaft bearing clearances are GOOD. Leave'm BEE........the amazed Dell
 
(quoted from post at 03:46:20 08/13/14) Bailey.......why are you surprized that oil pressure decreases as the oil warms up??? It's called VISCOSITY factor. ALL oil does that. That is why you now have multi-viscosity oil....ie 10-30wt. Remember, when the N-Engine was designed in 1939, it was spec'd for 6-qts of 30wt detergent and recommended a change to 40wt in HOT plowing weather. Surprizingly enuff, 30-40wt multi-viscosity oil does that automagically for you. 40psi when cold means yer oilpump AND crankshaft bearing clearances are GOOD. Leave'm BEE........the amazed Dell

Well, actually, I'm not terribly surprised that oil pressure (or viscosity) decreases with increased temperature, even though I'm using multigrade oil which should compensate for that a bit. My first concern (stated in an earlier post that got the suggestion to test the gauge, first) was that the oil pressure didn't just decrease but dropped all the way to 0 psi!!! Now I'm at least seeing something above 0 psi on the new gauge even when warm.

Nevertheless, I like your suggestion to "leave'm BEE". Now that I have the ole 8N running on all four cylinders, I just don't want to ruin it by running with low/no oil pressure! I figured someone with more experience on this forum than I have could give some advice.

Thanks.
 
The 216 Chevs of the early '50s had those bear claws on the rod caps. I showed someone one of them the other day.

Good oil pressure tractorial TOH !

Ford was in the lead :D
My 53 235 Chev . . . got the full pressure oil system with 48 psi -- no more dippers, in late '53 I think. But . . . Unfortunately with that 235, I got stuck with main bearing cap shimming as a rookie rebuilder . . . but I did it right.
Machine shops had those precut brass shims in their attics. :)

I know yours isn't an NAA but about oil,
my Jubilee owner's manual reads:
Your pressure guage should reach at least 40 psi at 1500 RPM
(just after reaching operating temp)
. . . and not read less than 8-10 at idle (450)

Cheers,
T
 
(quoted from post at 23:37:10 08/12/14)
(quoted from post at 03:46:20 08/13/14) Bailey.......why are you surprized that oil pressure decreases as the oil warms up??? It's called VISCOSITY factor. ALL oil does that. That is why you now have multi-viscosity oil....ie 10-30wt. Remember, when the N-Engine was designed in 1939, it was spec'd for 6-qts of 30wt detergent and recommended a change to 40wt in HOT plowing weather. Surprizingly enuff, 30-40wt multi-viscosity oil does that automagically for you. 40psi when cold means yer oilpump AND crankshaft bearing clearances are GOOD. Leave'm BEE........the amazed Dell

Well, actually, I'm not terribly surprised that oil pressure (or viscosity) decreases with increased temperature, even though I'm using multigrade oil which should compensate for that a bit. My first concern (stated in an earlier post that got the suggestion to test the gauge, first) was that the oil pressure didn't just decrease but dropped all the way to 0 psi!!! Now I'm at least seeing something above 0 psi on the new gauge even when warm.

Nevertheless, I like your suggestion to "leave'm BEE". Now that I have the ole 8N running on all four cylinders, I just don't want to ruin it by running with low/no oil pressure! I figured someone with more experience on this forum than I have could give some advice.

Thanks.

Engine oil pressure is an indirect indicator of bearing clearances. Hot idle oil pressure of 5 PSI on an N-series indicates an increase in bearing clearances over new. A fresh engine should hold 15-20 PSI or better.

TOH
 
(quoted from post at 16:03:11 08/12/14)
(quoted from post at 15:18:47 08/12/14)
(quoted from post at 15:01:04 08/12/14) So, thanks to advice from the Forum, I found an
oil pressure gauge at TSC to check my oil pressure
issue -- pretty good when first started, 0 after
warmed up. I suppose I still have a problem, of
sorts, but with new gauge installed I get 40 psi
at half throttle when cold, drops to 15-20 psi at
half throttle when warm, and about 5 psi at idle.
It"s definitely NOT 0 psi at idle, but it still
isn"t very good. I"ll have to decide whether I
have enough nerve to go through the oil pump or
replace bearings. . . .

Oh, nobody told me that the oil would spurt all
over me when I cranked it up without gauge but
with a dish under the the open end of the line!!!
That was a mixed blessing: good pressure, messy
tractor.

I've heard before from machine shops that the old saying was you need 10lb of oil pressure for every 1,000 rpms. so 5 psi at 450 rpms would be in line with that school of thought

Next time someone tells you that ask them how an old splash lubricated B&S lawn mower engine running at 3600 governed RPM survives with ZERO oil pressure???

My guess is anyone that knows the correct answer to the lawn mower question won't volunteer that "old saying".

TOH

for the record that saying originated with Smokey Yunik and was intended to apply to SBCs
 
(quoted from post at 07:13:26 08/13/14)
(quoted from post at 16:03:11 08/12/14)
(quoted from post at 15:18:47 08/12/14)
(quoted from post at 15:01:04 08/12/14) So, thanks to advice from the Forum, I found an
oil pressure gauge at TSC to check my oil pressure
issue -- pretty good when first started, 0 after
warmed up. I suppose I still have a problem, of
sorts, but with new gauge installed I get 40 psi
at half throttle when cold, drops to 15-20 psi at
half throttle when warm, and about 5 psi at idle.
It"s definitely NOT 0 psi at idle, but it still
isn"t very good. I"ll have to decide whether I
have enough nerve to go through the oil pump or
replace bearings. . . .

Oh, nobody told me that the oil would spurt all
over me when I cranked it up without gauge but
with a dish under the the open end of the line!!!
That was a mixed blessing: good pressure, messy
tractor.

I've heard before from machine shops that the old saying was you need 10lb of oil pressure for every 1,000 rpms. so 5 psi at 450 rpms would be in line with that school of thought

Next time someone tells you that ask them how an old splash lubricated B&S lawn mower engine running at 3600 governed RPM survives with ZERO oil pressure???

My guess is anyone that knows the correct answer to the lawn mower question won't volunteer that "old saying".

TOH

for the record that saying originated with Smokey Yunik and was intended to apply to SBCs

I didn't know that but it sounds very likely. There is a real basis for that saying and I am sure Mr Yunik understands it. I started to elaborate on it in my previous post but I didn't. In a modern engine you need oil pressure for things other than journal bearings. My BMW DOHC twin turbo engine cranking upwards of 7K needs LOTS of oil pressure - probably as much if not more than one of Mr Yunik's SBC's ;-) As long as you understand that distinction and what parts of the engine are being serviced by that pressure the saying is reasonable. But most people don't and it confuses them - particularly when we are talking about a flat head Ford.

That said, I DO NOT subscribe to the theory that 5 PSI running oil pressure in an N-series engine is fine. Even the flathead needs enough oil pressure to generate some spray lubrication for the cylinder walls and valve train and that is probably something around 20 PSI. The lubrication system in the flathead is more than capable of producing 30+ PSI in a good tight engine. If it isn't you either have a weak oil pump or excessive bearing clearances - possibly both. It may run like that for a very long time but it is clearly telling you it is worn internally. If you have a newly rebuilt flathead engine that isn't producing 30 PSI at operating speed you missed something in the rebuild. JMO.

TOH
 

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