Hi guys, this is my first post!

What are the weaknesses of the 351/400 engines?
Why does it seem to have such a bad reputation among Ford fans?

The one in my 1978 250 4x4 went 375 000 kms.
We recently rebuilt it, finding that the block and both heads were cracked. And it still had power when we pulled it out!
You must understand that this engine was HEAVILY ABUSED for 20 years as a farm truck.

Thoughts?
Thanks!

1978 f250 4x4-351 modified

 

Matt, Welcome aboard, Make yourself at home.

Seems to me that you answered your on question. An FE would have come out with no cracks. :-)

John
jowilker
Club FTE since 01 01

NC Chapter


66 F100s
In the still cool hours of the night,
you can hear chevys rusting away.

 

I fugured that this was the response I would get!! Is this the only problem with the M engines, that they are prone to cracking?
Thanks!

1978 F250 Ranger 4x4
351M

 

Couple of reasons that they are not in favor, the factory tried to make a smog motor out of 'em, low compression, retarded timing, heavy and not much in the way of performance out of the box. However, many report 0-5 psi oil pressure when warm, they still run for many, many miles without any complaints, knocking tapping ect., try to run just about any other engine showing 0 psi and they don't last long! Mine ran this way for quite a few miles before I rebuilt it. These can be made to run very well as a truck engine, simple mods like crank and pistons to make a 400cid, HV oil pump, aftermarket timing set run straight up, RV type cam, roller rocker conversion, good intake and carb with headers and dual exhaust along with a little milling to get the comp. up will really wake up these engines. I also don't think that many other engines with cracks in the heads and the block would have made it very far around the farm either-just another tribute to the toughness of the engine when used hard in the way you have, as a truck motor. These don't make very good high RPM motors without many, many mods to all the major engine systems, but, like anything thing else, it can be done, just cost a lot more. Aftermarket doesn't support these like some of the other engine families either, which doesn't help, but, good parts are out there, once again, cost a little more. Personally, I kept mine when the 460 went in, for me it's just treated me to well to give it up unless the "right" offer comes along! Had also thought about puttin' it in the '83 ranger, but that's just a thought, don't think I could ever shoehorn that thing in there! Have 150,000 miles when pulled and still had good, even compression across the board and didn't use any oil, and this in a 4x4 that does see off-road use whenever possible. Only real problem I had was with intake sealing, just liked to eat them gaskets around the intake ports, #6 both times, however, this is the easiest engine I've ever changed intake gaskets in.

 

The 351M/400 motors are a tough motor, even if they're not too powerful in stock form. We have one in a ranch truck that suffers from low oil pressure when warm, but still runs great and pulls strong. Around here there are a lot of older Fords running around with these motors and I don't hear any complaints about the engines.

 

Don't have much experience with the modifides but I do remember reading an article in a major performance magazine saying that the stock heads on a 4bbl. 400M flowed good enough for something like a 450HP buildup. Might be nice to know

 

Go to the 35m/400 forum and see what bill-beyer has to say about
M motors. Where are you bill? This your chance, another potiential convert is waiting!

 

>What are the weaknesses of the
>351/400 engines?
>Why does it seem to have
>such a bad reputation among
>Ford fans?
>
>The one in my 1978 250
>4x4 went 375 000 kms.
>
>We recently rebuilt it, finding that
>the block and both heads
>were cracked. And it
>still had power when we
>pulled it out!
>You must understand that this engine
>was HEAVILY ABUSED for 20
>years as a farm truck.

With the exception of blocks cast in the Michigan Plant prior to 3/77 M blocks aren't any more prone to cracking than any other thinwall cast blocks. The M heads do seem to be a little more prone to cracking than C heads so I would definitely spend the "bux to flux" before dumping any money in them. That being said the M series was a stop gap smog motor which couldn't make the transition to computer controlled emissions easily so it died.

With an increase in compression, decent cam, 4V and headers they will pull incredibly strong. The stroke is longer than any FE or 385 motor and the heads flow better than just about any head short of an aftermarket hi-po, high $$$ unit.

 

>
>With the exception of blocks cast
>in the Michigan Plant prior
>to 3/77 M blocks aren't
>any more prone to cracking
>than any other thinwall cast
>blocks. The M heads do
>seem to be a little
>more prone to cracking than
>C heads so I would
>definitely spend the "bux to
>flux" before dumping any money
>in them. That being said
>the M series was a
>stop gap smog motor which
>couldn't make the transition to
>computer controlled emissions easily so
>it died.
>
>With an increase in compression, decent
>cam, 4V and headers they
>will pull incredibly strong. The
>stroke is longer than any
>FE or 385 motor and
>the heads flow better than
>just about any head short
>of an aftermarket hi-po, high
>$$$ unit.

Well said, a M engine on it's deathbed is worth 2 FE's
How many FE's can make 385 HP and 475+ ftlbs of torque on a 2 bbl and exhaust manifolds?

 

Well I don't have an M motor, I've been playing w/ 302's and a 390. But my dad had a 78 Lincoln w/ 400 and that motor was a great runner in the Lincoln. He pulled a 36' travel trailer around w/ it, and the car was also plenty peppy w/ no load and a heavy foot. His Lincoln stayed dead stock as well no 4V or headers. BTW... I've seen 429 shoved into Ranger... surely the 351M will fit. I thought that block was the same length as 302 and 351W,C....? Just use a hammer on the tranny tunnel. I think if you are rebuilding a 351M you should be able to choose pistons to raise compression and short of replacing crank, undo the alleged shortcomings of the M motor. Or maybe it's time to put in a 385series motor?

BBT

 

PROJECT BRONCO.COM HAS SOME GREAT STUFF ABOUT A 351M400 ALSO LOOK AT ACCELERATED MOTION.COM

 

I had a 351m in my 79 F-150 4x4. It ran perfectly (burned a bit of oil) and pulled and hauled a good bit with it. At around 145000 miles it began to run very low oil pressure when warmed up. I switched to 20w50 and that helped a bit. Eventually I took it out (155000- still running fine) and put in a ford remanufactured 400 from a 78 F-250 4x4. I am not an engine expert or extream high performance expert, but both engines are definatly durable and are plenty powerful for most real tasks. Also I usually see more aftermarket parts for them over FEs. My friends 360 needed a new crankshaft at 160000 so every engine can have its faults. This is just my oppinion, I think the 351m and 400 are fine engines.

Vern

 

My dad has a 400M in his 79 4X4 and it suffered the very common "low oil pressure after it warmed up" symptom, but no other problems. He took it out and rebuilt it for very little money and put a 351 Cleveland HO cam in it and it now it is a totally different engine. It has more low end torque as well as much more mid range umphhh. I think they are perfectly fine engines. They aren't as proven as Windsor's or 385's but they are not bad, especially if that's what you already have and you don't have a ton of money.

 

This is just my 2 cents...I recently replaced the 351m in my 78' F150 4X4 with a 400M, alum intake, Holly 4BBL, stock manifolds, Dual 2.5" exhaust, K&N filter..This is one strong motor. The old one was replaced with 156K good oil pressure, 3 or more spun cam bearings laying in the muck at the bottom of the oil pan. I drove this thing from NC to NY at 70-85 MPH with them soaking below...Remember I still had great oil pressure??? Go figure. I only found this out because we pulled the motor to reseal it, I was using synthetic oil. Cleaned way to much I guess.

 

I love these posts I have my second 400 right now, its only 4000 miles old..The first I installed an edelbrock performer cam, carter625 4bbl carb, 2.5" exhaust,alum intake, K&N filter...I also removed all the emission crap like EGR, sensors , warm air tubing etc etc, and replumbed the vaccum lines to bare bones essentials... the extra vaccum helps those secondaries really open quick!!
with 2.75 rear axle, the truck would cruise at 120MPH!!! and I still had some throttle left... I must add that I put the truck on a diet by removing the midship gas tank, A/C compressor, evaporator,condenser,etc..(upkeep on an AC in south TX is too much work)the aluminum intake swap was a good weight loss plan
too!!
I threw a rod bearing and broke the cam in half at 100 mph after leaving a bowtie behind on hwy 87 to San Antonio...I was pleased that he didnt get to see me broke down, but the engine was very tired , it had over 250K on it.
I have recently found some 10:1 pistons for the 400 ITS ABOUT TIME!!!!!!!

https://www.ford-trucks.com/dcforum/User_files/3a9df0394b631ce6.gif






77'FORD F150 XLT 400