Engine ID 351M/400 crankshaft image

jimko

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I figured and hoped someone could tell me if this marking on the rear bearing cap might indicate the engine in my daughter's 78 Bronco. I removed the oil pan and fortunately the crank rotates easily with the plugs out so the next thing is to ID the motor. There was an article I recall saying there would be a stamping on the counter balance weight but there wasn't. The Bronco was given to her and the story was it hadn't passed smog so it was parked a few years ago when still running. The oil was clean and the coolant was clean and full plus it released pressure when I removed the radiator cap. Externally the engine has chewed plug wires and some leads that are missing from rats or mice chewing and there had been a nest on top of the motor. I am cleaning up all the mess and I pulled the starter which wouldn't crank when I jumped it. I also am not sure what Ca smog requires but there was no smog pump in 78 as I recall and just wish that it didn't need to be smogged.

I appreciate all the knowledge on this site!

Jim
 

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miesk5

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Yo Jim,
All I can offer is;
"M-block engines have the taller intake manifold front mating surface (almost an inch above the distributor mounting hole and front cover housing) and is quite apparent
  • The only real differences between a 351M and a 400 are the crank and the pistons.​
  • 351M and 400 heads are identical, are also nearly identical to 2V Cleveland heads​
  • The 351M and almost all 400's have the large bell housing pattern like the 429/460.​
  • The only 100% positive way to tell if you have a 351M or 400 is to drop the oil pan and check the casting numbers on the crank. They should be on the side of the first counterweight. A 400 crank will have 5M, 5MA or 5MAB casting code. A 351M crank will have a 1K casting code." @ https://www.fordification.com/tech/engineID-V8.htm

&
"Ford used the same components (engine blocks, cylinder heads, manifolds, etc.) to make both 351M and 400 engines. Therefore, you cannot rely on the casting ID codes or part numbers of any external component to distinguish a 351M from a 400.
Any 400 manufactured in any year can be rebuilt as a 351M by simply substituting the 351M crankshaft and pistons for the 400 parts.
Engine ID tags and calibration stickers are easily swapped from one engine to another, and even if they are not swapped, there is no way to tell whether an engine was rebuilt with 351M components without looking at the crankshaft.
The following table lists M-block crankshaft part numbers and casting ID codes.​
Model Year​
Part Number​
Casting ID​
Notes​
1971​
D1AE-6303-A​
5M​
Original 400 crankshaft.​
1972-1973​
D2AE-6303-A​
5MA
5MAB​
400 crankshaft, car only.​
1974-1977​
D4AE-6303-B​
5MA
5MAB​
400 crankshaft, car only.​
1975-1976​
D5AE-6303-A​
1K​
Original 351M crankshaft.​
1977-1982​
D7AE-6303-A​
1KA​
All '77-up 351M car and truck.​
1977-1982​
D7TE-6303-A​
5MA
5MAB​
All '78-up 400 car and '77-up 400 truck.​
M-block crankshaft casting ID codes are located on either the first counterweight (opposite the first throw at the front of the engine), or on the side of the first throw. Casting ID codes are recessed into the unfinished (raw cast) surface. Sometimes the characters are faint, so you may have to thoroughly clean the area with a solvent to find the ID code.
All 351M and 400 crankshafts are interchangeable, as long as you use the corresponding pistons. You can use any 351M or 400 crankshaft in any M-block engine block. Main bearings are different for '77-up truck blocks (D7TE) and '78-up car blocks (D8AE)."
@ http://grantorinosport.org/BubbaF250/parts/parts03.html
 

johnnyreb

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I figured and hoped someone could tell me if this marking on the rear bearing cap might indicate the engine in my daughter's 78 Bronco. I removed the oil pan and fortunately the crank rotates easily with the plugs out so the next thing is to ID the motor. There was an article I recall saying there would be a stamping on the counter balance weight but there wasn't. The Bronco was given to her and the story was it hadn't passed smog so it was parked a few years ago when still running. The oil was clean and the coolant was clean and full plus it released pressure when I removed the radiator cap. Externally the engine has chewed plug wires and some leads that are missing from rats or mice chewing and there had been a nest on top of the motor. I am cleaning up all the mess and I pulled the starter which wouldn't crank when I jumped it. I also am not sure what Ca smog requires but there was no smog pump in 78 as I recall and just wish that it didn't need to be smogged.

I appreciate all the knowledge on this site!

Jim
That is a crank bearing cap. Its the same letter on my 78 bronco cap. Also I don,t think (I don,t live in California) they also did not have a catalic converter. I could be wrong,but I thought I read their wasn,nt. Good luck.Mine looks about the same shape. I,m getting ready to rebuild mine too..Good luck.Go to Bubba,s and he has alot of information on the 351 and 400 and he tells all the difference and about numbers. I know the crank is different. Don,t know about the crank bearing caps.Good luck.
 

jimko

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That is a crank bearing cap. Its the same letter on my 78 bronco cap. Also I don,t think (I don,t live in California) they also did not have a catalic converter. I could be wrong,but I thought I read their wasn,nt. Good luck.Mine looks about the same shape. I,m getting ready to rebuild mine too..Good luck.Go to Bubba,s and he has alot of information on the 351 and 400 and he tells all the difference and about numbers. I know the crank is different. Don,t know about the crank bearing caps.Good luck.
I was expecting to see a number on one of the crankshaft counterweights but there wasn't any. Now I'm thinking a Marti report will indicate which motor this is.
 

johnnyreb

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I was expecting to see a number on one of the crankshaft counterweights but there wasn't any. Now I'm thinking a Marti report will indicate which motor this is.
CHECK AND SEE IF THE VIN NUMBER MIGHT BE ABLE TO TELL YOU. aLSO CHECK THE VALVE COVERS (IF THE STICKER IS ON IT) and see what it says, You can also check the rod length. That is another difference between the 351 and 400. Now someone could have changed the valve cover for a 400 marking. Check out BUBBA,S SIGHT . He has alot of info on the differencer between the two. Just type in--the address bar 400 ford motor--Bubba and many things you,ll see. about the 351 and 400.
 

OX1

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Easy enough with oil pan off to just measure how far a piston moves up/down.
CAREFULLY use a long blunt screwdriver in a spark plug hole and watch to see when you are
at TDC on any piston. Measure from bottom of piston to some convenient spot. Now do it again
at BDC. 1/2 inch longer for a 400 vs 351M (4.00" vs 3.50").
 
Last edited:

wobbly-pop

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Yo Jim,
All I can offer is;
"M-block engines have the taller intake manifold front mating surface (almost an inch above the distributor mounting hole and front cover housing) and is quite apparent
  • The only real differences between a 351M and a 400 are the crank and the pistons.​
  • 351M and 400 heads are identical, are also nearly identical to 2V Cleveland heads​
  • The 351M and almost all 400's have the large bell housing pattern like the 429/460.​
  • The only 100% positive way to tell if you have a 351M or 400 is to drop the oil pan and check the casting numbers on the crank. They should be on the side of the first counterweight. A 400 crank will have 5M, 5MA or 5MAB casting code. A 351M crank will have a 1K casting code." @ https://www.fordification.com/tech/engineID-V8.htm

&
"Ford used the same components (engine blocks, cylinder heads, manifolds, etc.) to make both 351M and 400 engines. Therefore, you cannot rely on the casting ID codes or part numbers of any external component to distinguish a 351M from a 400.
Any 400 manufactured in any year can be rebuilt as a 351M by simply substituting the 351M crankshaft and pistons for the 400 parts.
Engine ID tags and calibration stickers are easily swapped from one engine to another, and even if they are not swapped, there is no way to tell whether an engine was rebuilt with 351M components without looking at the crankshaft.
The following table lists M-block crankshaft part numbers and casting ID codes.​
Model Year​
Part Number​
Casting ID​
Notes​
1971​
D1AE-6303-A​
5M​
Original 400 crankshaft.​
1972-1973​
D2AE-6303-A​
5MA
5MAB​
400 crankshaft, car only.​
1974-1977​
D4AE-6303-B​
5MA
5MAB​
400 crankshaft, car only.​
1975-1976​
D5AE-6303-A​
1K​
Original 351M crankshaft.​
1977-1982​
D7AE-6303-A​
1KA​
All '77-up 351M car and truck.​
1977-1982​
D7TE-6303-A​
5MA
5MAB​
All '78-up 400 car and '77-up 400 truck.​
M-block crankshaft casting ID codes are located on either the first counterweight (opposite the first throw at the front of the engine), or on the side of the first throw. Casting ID codes are recessed into the unfinished (raw cast) surface. Sometimes the characters are faint, so you may have to thoroughly clean the area with a solvent to find the ID code.
All 351M and 400 crankshafts are interchangeable, as long as you use the corresponding pistons. You can use any 351M or 400 crankshaft in any M-block engine block. Main bearings are different for '77-up truck blocks (D7TE) and '78-up car blocks (D8AE)."
@ http://grantorinosport.org/BubbaF250/parts/parts03.html
its easy one has a 3.5 inch ****** and the other a 4"" ******. simple tape measure
 

johnnyreb

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I looked om mine today. Towards the rear and all I found was 32. Then my cousin son came down and as I was turning the crank buy the rear of the crankshat,. He spotted the letter tward the front. Mine is a 400 and was measured from from the top to the bottom 4 inches. I have the heads off.He took a picture of it and when I get it. I,ll try and send it.
 

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johnnyreb

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Easy enough with oil pan off to just measure how far a piston moves up/down.
CAREFULLY use a long blunt screwdriver in a spark plug hole and watch to see when you are
at TDC on any piston. Measure from bottom of piston to some convenient spot. Now do it again
at BDC. 1/2 inch longer for a 400 vs 351M (4.00" vs 3.50").
Mine measuerd 4 inches and had the same letters--I THINK MAB soming that you had posted Mike. Thanks alot.
 

johnnyreb

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I looked om mine today. Towards the rear and all I found was 32. Then my cousin son came down and as I was turning the crank buy the rear of the crankshaft,. He spotted the letter tward the front. Mine is a 400 and was measured from from the top to the bottom 4 inches. I have the heads off.He took a picture of it and when I get it. I,ll try and send it.
I hope I got it.Hear is the marking on my crank
 

johnnyreb

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markings on crank shaft 78 bronco
 

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  • 1978 Ford Bronco 400 motor marking.jpg
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