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Old May 1st, 2008, 08:34 PM   #1
BATLWGN
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Default 351M reliability?

I recently acquired my first Ford. I have heard some opinions on the 351M and thought I would ask for more. Are they a decent or junk motor?

Discuss.
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Old May 1st, 2008, 08:44 PM   #2
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While they certaintly are not one of Henry's best,They really are not that bad. With The right cam they actually are a great torque engine, Just don't overwind them. For some extra protection plum the oil ports together with a hard line,The one on the side of the block near the fuel pump to the one on top in the rear. If you really want to see some power out of it I can find the part # to the Elgin cam that was recommended to me by a very knowledgeble and well know engine builder that will turn your dog into a tire smoking monster.
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Old May 1st, 2008, 08:59 PM   #3
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I like them. I've had two, and they have gotten great mileage and reliability. However they aren't the most powerful.

My 1978 F-150 extended cab longbed 4x4 with a 351M, C6, 3.50 gears and 35 inch tires got an honest 20 MPG. It is currently getting a new motor, and a swap over to a 4 speed.

And PLEASE do not start going around calling your motor a 351 Modified. You will just sound like an idiot to those that know better. The M on the 351 and 400 motors stands for Midland.

About the only thing to watch out for is the old stock 2 barrel carb. Although a good carb with nice power, it tends to stick the float open, pouring gas down your intake and ruining your engine if you are not careful. That is what happened to mine when my brother borrowed it.
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Old May 1st, 2008, 10:27 PM   #4
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They're heavily modeled after the famous Cleveland engines. it's almost basically a Cleveland on steroids, taller deck height, room for more stroke (on the 400M's at least). they're just choked down for emissions, a little work and some careful choosing of parts to let it breathe a little more and they'll really wake up for power. They're not a bad engine at all, just needs some love.

Mods I'd suggest, if possible get some new pistons and have some block work done, IIRC, the quench is seriously janked on these engines (Ford's attempt at improving emissions) the block may need decked and some new replacement cast pistons in order to make sure the CR doesn't get too crazy. for example the 250 I6's piston, some are almost 1/4" down in the cylinder bore, no joke.

Thats probably the biggest mod, but it's rather invasive, otherwise:

Bigger carb, headers, make sure the ignition is a good HEI like duraspark (I don't think they had it?)

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Old May 1st, 2008, 10:54 PM   #5
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Duraspark is what I have on my 78. I believe it was stock.

Hot Rod Mag did a buildup of a 400 awhile ago. It was a screamer when it was done.

The history of the Midland motor is actually fairly interesting. It was orignally designed off the Cleveland design, to replace the 429/460. Tons of reasearch was put into the heads, to make them the best flowing head ever for the fords. Then 1972 came along, with the emissions crunch, so the design was re-worked as an emission motor for the 1975 Cars, and then the 1977 trucks. It can be re-awakened though.

Neat fact that most don't realize. M heads will bolt onto a 351C block. If you use a vintage boss or Nascar bathtub intake, you have a 351 Boss motor.
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Old May 2nd, 2008, 05:23 PM   #6
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Well, it runs really well and I am not planning on doing any internal engine work unless needed. It needs some carb work and I was thinking of just putting an Edelbrock intake and Holley carb on it. That was about it.

I have had some people tell me their oiling system sucks and they have weak cranks. I was just trying to get more opinions of these motors.


On a side note: I noticed a couple of posts about D60's in the front of a 78 F250 and came across that the factory had a plow option with the 60. Well, it has a plow on it with paperwork from '78 and has a D60 under the front, so I am concluding that it may very well be a factory plow package. Anyone have more info on these? I was just getting ready to google them.
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Old May 2nd, 2008, 05:33 PM   #7
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The 351m is a modified. There is no M on the 400. Tags on the original valve covers said engine family 351m/400. I have seen them called Milford, Michigan, Muskegon and just read an old mag that called it a Midland that was the 1st time I ever heard that Had a couple 351m's I like the 400 better but it did not get near the 17mpg my 78 f150 would get. I guess thats because it was putting more out than twice the power of the 351's I had. I used a sig erson tq20 cam edelbrock performer cam 750 holley long tube headers and a b & m torque plus converter. Truck would smoke 5.0 stangs and irocs to over 100mph.
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Old May 2nd, 2008, 06:09 PM   #8
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The 351m is a modified. There is no M on the 400. Tags on the original valve covers said engine family 351m/400. I have seen them called Milford, Michigan, Muskegon and just read an old mag that called it a Midland that was the 1st time I ever heard that Had a couple 351m's I like the 400 better but it did not get near the 17mpg my 78 f150 would get. I guess thats because it was putting more out than twice the power of the 351's I had. I used a sig erson tq20 cam edelbrock performer cam 750 holley long tube headers and a b & m torque plus converter. Truck would smoke 5.0 stangs and irocs to over 100mph.
The 400 is also an M motor. It is in the same Midland engine family. The only difference in the two is the crank and rods. The 400 doesn't put out twice the horsepower. It puts out 160 versus the 351's 130. However the additional stroke of the 400 did increase the torque greatly, but I don't know the numbers off hand. You are correct that others have called them by different incorrect city names, however they have never been called a "modified" by Ford. Unfortunately, the term became common in the late 70's when an errant Chilton's writer mistakenly announced that the M stood for "modified".
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Old May 2nd, 2008, 08:28 PM   #9
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I know they will take a beating and then some. You can even tun then long after they start knocking and they will still run for a while.
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Old May 3rd, 2008, 11:35 AM   #10
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I know they will take a beating and then some. You can even tun then long after they start knocking and they will still run for a while.
I had one , didnt like it ?? to each there own I guess...:chiefwoohaw:
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Old May 5th, 2008, 11:40 AM   #11
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[It puts out 160 versus the 351's 130]

These figures may be correct for a stock motor mine was not exactly stock. Car Craft dynoed a mildly built one at 390+HP. 351M'S and 400'S are the same engine family but the 400 came out a few years earlier and was the only 400CID Ford engine so there was no need for a letter to tell what motor it was. I was told by a person who has worked on Fords exclusively since the 60's that the 351M was a modified 400. Where did Midland come from? Never heard of Ford having an engine plant there. I would have to see some evidence before I am going to call it anything but a 351 modified
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Old May 5th, 2008, 11:43 AM   #12
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junk engine. Swap it out for a 351w to make power. There are hardly any parts available for the M and they are expensive.
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Old May 5th, 2008, 06:13 PM   #13
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junk engine. Swap it out for a 351w to make power. There are hardly any parts available for the M and they are expensive.
Incorrect.

reliable and will run for forever.
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Old May 6th, 2008, 01:19 AM   #14
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I'm not saying the M can't be built up. More parts are offerd for a W or C and can be had anywhere! also they do not cost as much.
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Old May 6th, 2008, 08:58 PM   #15
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I'm not saying the M can't be built up. More parts are offerd for a W or C and can be had anywhere! also they do not cost as much.

This isn't what I was asking though. I have had numerous people tell me it can be built but with $$$. I am not looking to build a powerhouse motor. It is in an old plow truck and runs great as is. I am just asking for any problems to look out for on a factory motor.
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Old May 6th, 2008, 09:56 PM   #16
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Long tube headers, good cam, good carb and intake. Mine ran like a top for 15 years. Let water seep in like an idiot. I got a 460 for cheaper than I could have redone the 351M.
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Old May 7th, 2008, 08:45 AM   #17
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Quote:
Originally Posted by BATLWGN View Post
This isn't what I was asking though. I have had numerous people tell me it can be built but with $$$. I am not looking to build a powerhouse motor. It is in an old plow truck and runs great as is. I am just asking for any problems to look out for on a factory motor.
It should run for a plenty long time. I'd still put a new carb and headers on it though if you happen get the chance. Those are easy bolt ons, and more than likely help the power a tad.
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Old May 7th, 2008, 11:27 AM   #18
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Both my 78 351M Bronco and my 79 Bronco with a 400 ran to over 200K. I sold the 78 with 200K on it and the guy drove it every winter for about 7 years. He left it parked in the weeds all summer then pulled it out when the snow started to fly and drove it all winter with no problems until the truck just rotted away.
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Old May 7th, 2008, 05:44 PM   #19
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Mine ran for 4 years with a max of 10psi oil pressure and 0 at idle. MANY mounds trips finally killed it.
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Old May 7th, 2008, 07:33 PM   #20
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Mine ran for 4 years with a max of 10psi oil pressure and 0 at idle. MANY mounds trips finally killed it.

This statement makes me happier. After it warms up, I am at about 5-10 at idle and 25-30 max going down the road. Not much better, but I guess I should get a few years out of it.

It reminds me of the AMC 360 in my wagoneer that I used to run gear oil in just to get some oil pressure.
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