I have a 79 F-150 with a 351M and am having serious oil pressure problems. I thought it was the guage so I replaced the stock one with a mechanical guage. I'm running 20W-50. When I crank it up I get 60 psi. As it heats up it creeps lower and lower until I can get 20 psi at 2000 rpms and no, repeat 0, oil pressure at idle. I didn't think oil pumps just went south on you, a friend told me it could be an oil relief valve stuck open in the oil filter housing. Does this sound right to anybody???? Thanks

 

[font size="1" color="#FF0000"]LAST EDITED ON 08-Jan-01 AT 02:41 PM (EST)[/font][p]beratte,

Oil pumps don't just suddenly go south, especially only at certain speeds. Since you have oil pressure at times, we know the gear and pump driving shaft are still OK . The oil pressure diminishes as the temp warms up, because the pump can't overcome the increased oil lost past the bearings (remember hot oil escapes from the bearings easier). Oil pumps can wear, but usually the real problem is engine bearing wear. It is possible that the relief valve could be stuck open, but the 351M400 engine family has a history of low oil pressure with high mileage engines. BTW, the relief valve is located inside the oil pump body on this engine -requiring oil pan removal to inspect.

If the engine truly has zero oil pressure, the crankshaft will not be riding on a film of oil, but on the bearings themselves! The resulting wear will increase, as this is a viscous circle. Also, without any oil pressure the hydraulic lifters would be collapsed making the rocker arms noisy.

A temporary solution is to install a high volume Melling oil pump - the industry leader in oil pumps. The proper fix is installing new main, rod, and sometimes cam bearings as well on a newly ground crankshaft as well as the HV oil pump. While you are in there, check the timing chain, too - but it's really easy to get really "involved" from there on...

Been there, done that.

Art

 

Thanks that's good info. The engine is old, not sure how many miles. I think I may be quickly on the way to a new engine. Where's the best place to get a quality rebuild?

 

That's a really difficult question to answer. I have many friends who all went to various machine shops for repairs, exchanges, or speed-shop type work here in the Milwaukee area and most got lots of headaches. In fact, I think I know of a horror story for each shop around here that they went to! I went to an older machinist who was self-taught and much more expensive (2-3 times more)- he took the time to check and do things right and in the long run it saved me lots of $$$. Remember, it cost my friends time or money to pull their engine out and more money to get it repaired again and again while my race car is still running... Many times, you get what you pay for and don't shop for "price" instead of quality and guarantee.

I suggest looking for someone who will give you a solid guarantee with little "fine print". Ask around, such as at parts stores and other places that are in that line of work. Remember to ask yourself that if they recommend some place, why are they REALLY recommending it (to give themselves or their friend more work - or because the shop really did do a good job). Sometimes small garages who do repairs, but not any machine work, could direct you. Get several opinions!

I sincerely wish you luck, because I don't know of a single good shop around here anymore since my friend closed his machine shop.

Art

 

I second what he said about paying the price. I have a custom 428 FE engine that I had to pull because of bad PAW rods. I could have fixed the problem for $300, but I just gave the engine to a pro speed shop that does NOTHING but build race engines. I paid about $1,000 for the repairs and it runs GREAT! I wish I had gone to the pros first. The other option is to purchase a ready-made setup from Jasper engines or some famous place like that. I think Jasper has a great reputation and the cost shouldn't be that much more that others.

 

I'd stay away from Jasper rebuilds, as I had to fix a Jasper rebuilt C-6. The rebuilder must have paid no attention to the pump, because it had one heck of a suction leak and buzzing noise. Mismatch of parts caused by a technician asleep at the bench???

Art

 

sell the truck to me, and you won't have to worry about the rebuild.

Just yank the pan and put in a HV HP pump, it's a quick fix for the problem and you could keep driving it while you rebuild that 400M you found for $200 bucks.

Just my .02 cents

 

Ah the M block , what a great machine if you know how to make her happy. First of all nearley all stock M blocks have a serious oil pressure problem .The oil passages run from the oil pump to the cam bearings then to the rods and mains , unlike most other engines. The fix is to get more oil volume insted of pressure. You really need to have a machine shop oversize the galleries but most of use don't want to yank the engine. So you can pull the oil pan and oil pump and enlarge the oil pick up port under the pump from a 5/16" hole to a 3/8" hole, easy enough and then get your self a good HV pump you should see a great change. Your problem is probably worn cam bearings which allows too much clearence so if a rebuild is what you want then have a good shop take care of those oil galleries. As for rebuilt motors try your local auto parts store I know that here in Ohio I bought a long block 400m from Auto Zone for 699.00$ Good luck

 

You can normally run the engine like this for 2 years, even 3 sometimes, but should get it fixed, had one go up on me, a tow home from my dad and a new motor later and I was back on the road, replacing main bearings and rod bearings should fix it though and put in a high volume pump while you are at it.

 

in 1989 i bought a 79f-250 4x4 SuperCab with a 400 motor. this truck had the same problem and it was a snowplow truck.i know this is the cheap way out but what i found to work for me was. adding a bottle of this stuff called "MOTOR HONEY" after each oil changing.and if my oil pressure droped before the oil change was do(3000mi) i just added another bottle.i drove this truck like this from 1989-1996.and i also did snowplowing with it.and i beat the hell out of it.i planed on putting a 460 motor in it. i even got one and had the short block done. i was just waiting for the 400 to drop dead before i did the swap. but it never did. i ended up selling the truck because it was rusted out so bad.the truck had 175,000mi on it when i sold it.and it ran very good. and i bought another 78 F-250 SuperCab 4x4 with a 4" lift. but i dont snowplow with this one.

 

We just did a rebuild on my dads 400. I rebuilt the last 400 (just did essentials). It had the same symptoms you described. Good oil pressure when cold, but as soon as it warmed up, zero. We found another complete 400 for $50 and rebuilt it. Upon teardown of the old one, all of the bearings were into copper and we found 2 lifters worn out. We either got water in the oil (had milk) from a bad gasket, or defective lifters that sent metal through the bearings. Ah well. The 400 is a workhorse.




89 F150 4x4 300/4 speed 33.12.50 w/Rancho lift 3.55 gears
82 Mustang GT 302 C4 + nitrous=FAST
91 Mustang GT basic bolt ons- GM Eater

 

>Ah the M block , what
>a great machine if you
>know how to make her
>happy. First of all nearley
>all stock M blocks have
>a serious oil pressure problem
>.The oil passages run from
>the oil pump to the
>cam bearings then to the
>rods and mains , unlike
>most other engines. The fix
>is to get more oil
>volume insted of pressure. You
>really need to have a
>machine shop oversize the galleries
> but most of use
>don't want to yank the
>engine. So you can pull
>the oil pan and oil
>pump and enlarge the oil
>pick up port under the
>pump from a 5/16" hole
>to a 3/8" hole, easy
>enough and then get your
>self a good HV pump
>you should see a great
>change. Your problem is probably
>worn cam bearings which allows
>too much clearence so if
>a rebuild is what you
>want then have a good
>shop take care of those
>oil galleries.

Now why is it that of all the M block devotees I've had contact with not ONE of them said anything about enlarging any oil passages. The problem is NOT probably worn cam bearings it is most likely worn mains. Try to think logically for a second, how much wear is there going to be on a bearing which has virtually NO reciprocating motion i.e. the cam bearings vs a bearing with forces from 3.5" to 4" stroke rods flinging them all over the place i.e. the mains?

The answer to the M series (and Cleveland for that matter) oiling issues is oil RESTRICTION but only in motors that are going to see high revs (7000+). Maybe that's why there is a RESTRICTOR kit on the market for Clevelands and not a "Oil Passage Enlargement" kit.

The easiest fix is to keep the drill the hell away from the motor and simply add an additional oil line from the passage in front of the fuel pump to the O.P. sending unit port on the back of the block. Add in a T fitting so you can retain the O.P. sending unit and voila, you're done.

 

>The oil passages run from
>the oil pump to the cam bearings
>then to the rods and mains,
>unlike most other engines.

frank, et al,

Not true. This is just one of the bizarre popular rumors about the M-block. According to my Ford books, the M-block has the same oil system design as the 385 series (429/460) engines.

The oil passage from the oil filter feeds the front (#1) crank bearing first. All mains after #1 are fed by the right main gallery that runs from the front of the block to the back, after oil goes through the #1 main. All cam bearings are fed from their corresponding mains.

The oiling "problem" is that the pump feeds the front main well before the others. Rear mains and cam bearings are the last to get oil pressure. You can see this when you watch how long it takes for oil pressure to register after you first crank the engine, since the pressure sender is fed from the rear of the right main gallery, after all the mains are pressurized. The looser the bearings are, the longer it takes for the pressure to build up.

Running a secondary line from the filter adapter to the pressure sending hole at the rear of the block gets pressurized oil to the rear mains and rear cam bearings faster. I think this modification is worthwhile even for a stock-level buildup.

As for relatively cheap long block 400 rebuilds, you can get them from Ford dealers with a 2-year/24K mile warranty for a little over $1K.

BubbaF250

1980 F250 4x4 Custom, 351M/NP435/NP208/D44HD-TTB/D60-FF/3.55s 6750 GVW, Rust & White.

 

[font size="3" color="#191979"]

Bill, I said the things I did because I have been there myself. I do not dream up "wild goose chases" to send people on, rather I try to share my experiences with them to try to help them out. The cam bearings on my 1979 F250 4WD were severly worn as well as the main & rod bearings, so I mentioned those may need replacement as well in my reply to "beratte". The point I am trying to make to him is that the low oil pressure is caused by too great of bearing clearance compared to the oil available from the pump. A drill is a good tool when used correctly. Drilling out the oil passages that are too small from the factory reduces pressure drops, making the oil pump "see" a more correct engine oil pressure which prevents the relief valve from opening too early. This in turn causes the high volume pump to deliver more oil to the bearings instead of just circulating the additional oil within the pump. Just ask anyone who has an 7000 RPM 7+ liter engine (I have two) about whether a drill is required or not.

BTW, the main and rod bearings are not reciprocating motion, nor are they oscillatory motion - they rotate in one direction just like the cam bearings do. Take another look - it's the kinematics of the mechanism!

Art

 

>Bill, I said the things I
>did because I have been
>there myself. I do
>not dream up "wild goose
>chases" to send people on,
>rather I try to share
>my experiences with them to
>try to help them out.
> The cam bearings on
>my 1979 F250 4WD were
>severly worn as well as
>the main & rod bearings,
>so I mentioned those may
>need replacement as well in
>my reply to "beratte".
>The point I am trying
>to make to him is
>that the low oil pressure
>is caused by too great
>of bearing clearance compared to
>the oil available from the
>pump. A drill is
>a good tool when used
>correctly. Drilling out the
>oil passages that are too
>small from the factory reduces
>pressure drops, making the oil
>pump "see" a more correct
>engine oil pressure which prevents
>the relief valve from opening
>too early. This in
>turn causes the high volume
>pump to deliver more oil
>to the bearings instead of
>just circulating the additional oil
>within the pump. Just
>ask anyone who has an
>7000 RPM 7+ liter engine
>(I have two) about whether
>a drill is required or
>not.

If you don't want to send him on a wild goose chase then don't tell him to start drilling out oil passages because that's exactly what that is. A drill is an indispensable tool but not when you're trying to improve the oiling system on a 335 series unless you're drilling the passage out to add a restrictor. I don't care which "experts" you talked to I'll take Jack Roush's experience making high performance Ford engines and put it up against anyone. He makes a restrictor kit SPECIFICALLY for Clevelands to make them live at high RPMS. Since the M block shares the same oiling system I'm sure it would work for them also.

In the meantime all that needs to be done for any street motor is put away the drill and purchase a couple of AN fittings and some quality line and a T fitting and run a secondary line from the oil passage in front of the fuel pump to the O.P. sending unit port.

>BTW, the main and rod bearings
>are not reciprocating motion, nor
>are they oscillatory motion -
>they rotate in one direction
>just like the cam bearings
>do. Take another look
>- it's the kinematics of
>the mechanism!
>


Of course the mains don't oscillate or reciprocate, I never said they did. However the forces acting on them from the cranks throws which convert vertical motion to rotary motion are significantly more stressful than the forces acting on the camshaft hence the tendency of the main & rod bearings to wear more.