351W ?'s
Posting Guru
Joined: Jun 1999
Posts: 2,415
Likes: 3
From: Comox Valley, Canada
I have read so many posts about this and just when I think I got it..... I think I am still confused....maybe 
Ok here is what I think I have learned about the 302/351W flexplate/flywheel interchangeability theory....
Harmonic balancers are matched to engine/rotating assembly and balance the rotating mass to eliminate the "clothes on one side of the washer during spin cycle wobble" So the correct Balancer must be retained with its engine..... 302 cant be swapped to 351W and vice versa.... unless of course they are the same weight........
Flexplates and flywheels are interchangeable regardless of weights.......... just have to be aware of different diameters/tooth count... and of course do not try to use a flexplate on a manual tranny......
So why are there different balance weights on them?
Are they dynamically balanced like tires/rims?
If so why aren't all the weights a little different due to manufacturing tolerances?
Ok here is what I think I have learned about the 302/351W flexplate/flywheel interchangeability theory....
Harmonic balancers are matched to engine/rotating assembly and balance the rotating mass to eliminate the "clothes on one side of the washer during spin cycle wobble"
So the correct Balancer must be retained with its engine..... 302 cant be swapped to 351W and vice versa.... unless of course they are the same weight........Flexplates and flywheels are interchangeable regardless of weights.......... just have to be aware of different diameters/tooth count... and of course do not try to use a flexplate on a manual tranny......
So why are there different balance weights on them?
Are they dynamically balanced like tires/rims?
If so why aren't all the weights a little different due to manufacturing tolerances?
I'll have the Roast Duck
Joined: Jul 2002
Posts: 9,622
Likes: 109
From: Northshore, MN
I would say they are. That's why engine balancers match the flywheel/flexplate to the crankshaft for a particular engine. Stroke a motor, and the counterweights on a crankshaft will change, thus the flywheel/flexplate should too.
Elder User
Joined: Jan 2008
Posts: 658
Likes: 0
From: N.W. Mo.
Flexplates and flywheels are interchangeable regardless of weights.......... just have to be aware of different diameters/tooth count... and of course do not try to use a flexplate on a manual tranny......
So why are there different balance weights on them?
Are they dynamically balanced like tires/rims?
If so why aren't all the weights a little different due to manufacturing tolerances?
Some crankshats are balanced without the help of weighting the flywheel and in those cases the flywheel is balanced within it's self much like balancing a tire/wheel.
Others use the flywheel as part of the ballancing process and these flywheels have weights added to them.
The same is true of the harmonic balancers on the front of the crank. Some are weighted and some are not. The 385 series engines came both ways depending on date of Manufacture.
Regardless of which flywheel or balancer you have it can be replaced but must be with one made for the same application.
All factory flywheels are manufactured to certain factory tolerances and are interchangeable with others made for that exact application.
When you have an engine balanced it will be balanced to much tighter tolerance than factory and later when changing parts the balance can be compromised and must be rebalanced to maintain the precise balance.
Post Fiend
Joined: May 2008
Posts: 7,641
Likes: 21
From: Poway, Ca.
I have read so many posts about this and just when I think I got it..... I think I am still confused....maybe
Ok here is what I think I have learned about the 302/351W flexplate/flywheel interchangeability theory....
Harmonic balancers are matched to engine/rotating assembly and balance the rotating mass to eliminate the "clothes on one side of the washer during spin cycle wobble" So the correct Balancer must be retained with its engine..... 302 cant be swapped to 351W and vice versa.... unless of course they are the same weight........
Close. The balance is MATCHED to a particular crank shaft. Some engines, my 390 Police Interceptor for example, has a heavier crank shaft than a stock 390 so it carries a different balance as well. So, on your 351W you need to use a balance specifically designed for your version of the 351W. And be sure to look at 351 Windsor balances. There was a big block 351 Cleveland Engine and a modification of that called a 351M in later models (What the "M" stands for is still in discussion - some say it stands for "modified" because it evolved from the Cleveland, others say it stands for the manufacturing plant where the engines were produced - no matter
).
Also, where the balance counterweight sits in relation to the crank shaft will vary. They are splined and fit only in one position. This can vary from size of engine to size engine as well. It goes with the crankshaft for that particular engine.
So, if you rebuild your FE 360 as an FE 390, it now has a 390 crankshaft, and you need to swap the 360 balance for a 390 balance.
Flexplates and flywheels are interchangeable regardless of weights.......... just have to be aware of different diameters/tooth count... and of course do not try to use a flexplate on a manual tranny......
I think you've got it right but just to clarify, flex plates can only be used with Automatic transmissions. Flywheels can only be used with Manual transmissions. Flex plates are interchangeable with other flex plates on different engines if they are of the same characteristerics. A flex plate from one engine that is the same diameter, has the same number of teeth, and has the same crank shaft bolt pattern can be used on any engine whos flex plate has the same characteristics and when used with a same transmission (like a C4 on both). So, theoretically, if you pull a flex plate off a 289, that is 11 inches in diameter, has 175 teeth and a concentric 6 bolt pattern with 1/2 inch bolt holes, then you can use that flex plate on any other engine that uses an 11 inch 175 tooth flex plate with a concentric 6 bolt patern and 1/2 inch bolt holes (and the same transmission as the original engine). Same story with Flywheels - but only on cars with manual transmissions
So why are there different balance weights on them?
See my note above about balances.
Are they dynamically balanced like tires/rims?
YES at the factory when produced. There are weight and balance criterion that each must meet before it is accepted.
If so why aren't all the weights a little different due to manufacturing tolerances?
Because in the manufacturing specifications, there is a range of weight and dynamic balance that the parts must meet to be accepted. Those specifications are determined by the engineers who design the engines. They may be very slightly variation, but all fall within the test specifications, so they can be interchangeable from engine to engine of the same type.
Ok here is what I think I have learned about the 302/351W flexplate/flywheel interchangeability theory....
Harmonic balancers are matched to engine/rotating assembly and balance the rotating mass to eliminate the "clothes on one side of the washer during spin cycle wobble"
So the correct Balancer must be retained with its engine..... 302 cant be swapped to 351W and vice versa.... unless of course they are the same weight........ Close. The balance is MATCHED to a particular crank shaft. Some engines, my 390 Police Interceptor for example, has a heavier crank shaft than a stock 390 so it carries a different balance as well. So, on your 351W you need to use a balance specifically designed for your version of the 351W. And be sure to look at 351 Windsor balances. There was a big block 351 Cleveland Engine and a modification of that called a 351M in later models (What the "M" stands for is still in discussion - some say it stands for "modified" because it evolved from the Cleveland, others say it stands for the manufacturing plant where the engines were produced - no matter
).Also, where the balance counterweight sits in relation to the crank shaft will vary. They are splined and fit only in one position. This can vary from size of engine to size engine as well. It goes with the crankshaft for that particular engine.
So, if you rebuild your FE 360 as an FE 390, it now has a 390 crankshaft, and you need to swap the 360 balance for a 390 balance.
Flexplates and flywheels are interchangeable regardless of weights.......... just have to be aware of different diameters/tooth count... and of course do not try to use a flexplate on a manual tranny......
I think you've got it right but just to clarify, flex plates can only be used with Automatic transmissions. Flywheels can only be used with Manual transmissions. Flex plates are interchangeable with other flex plates on different engines if they are of the same characteristerics. A flex plate from one engine that is the same diameter, has the same number of teeth, and has the same crank shaft bolt pattern can be used on any engine whos flex plate has the same characteristics and when used with a same transmission (like a C4 on both). So, theoretically, if you pull a flex plate off a 289, that is 11 inches in diameter, has 175 teeth and a concentric 6 bolt pattern with 1/2 inch bolt holes, then you can use that flex plate on any other engine that uses an 11 inch 175 tooth flex plate with a concentric 6 bolt patern and 1/2 inch bolt holes (and the same transmission as the original engine). Same story with Flywheels - but only on cars with manual transmissions
So why are there different balance weights on them?
See my note above about balances.
Are they dynamically balanced like tires/rims?
YES at the factory when produced. There are weight and balance criterion that each must meet before it is accepted.
If so why aren't all the weights a little different due to manufacturing tolerances?
Because in the manufacturing specifications, there is a range of weight and dynamic balance that the parts must meet to be accepted. Those specifications are determined by the engineers who design the engines. They may be very slightly variation, but all fall within the test specifications, so they can be interchangeable from engine to engine of the same type.
Good Luck,
J!
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
Likes: 784
From: Simi Valley, CA
I shoulda typed additional info.
C3AZ6375L .. 157 Tooth Flexplate.
Marked: C8OP-C / (4) 7/16" converter attaching holes on a 10 1/2" bolt circle / Use with case fill transmissions.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~
EOAZ6375A .. (replaced C5AZ6375T) .. 164 Tooth Flexplate.
(4) converter attaching holes on a 11 7/16" bolt circle / Use with pan fill transmissions.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~
Unrelated to 302/351W's:
1965/76 352/360/390 engines (car/truck) use the same flexplate (C5AZ6375D) with either C-O-M or C6 A/T's.
Some 1965/71 passenger cars w/352/390 engines use a 11" clutch, some use an 11 1/2" clutch.
1965/76 F100/350's 352/360's use an 11" clutch, all 1968/76 F100/350's 390's use an 11 1/2" clutch.
The 352/360 and 390 flywheels can be used either way without any ill effects.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
It must be a 1962/65 390 P/C (Police Cruiser) engine, otherwise that's not correct.
390 crankshafts:
C3AZ6303C = 1962/63 390 P/C & HiPo only.
C4AZ6303G = 1964/65 390 P/C only.
C3AZ6303B = 1961/63 390 (use before 11/1/1962)
C4AZ6303F = 1963/65 390 (use after 11/1/1962)
C6AZ6303A = 1966/76 390.
~~~~~~~~~~~~~~~~~
ALL 1963/67 352/390's except HiPo's use the same harmonic balancer whether a Police Cruiser or not:
C3AZ6312E. This includes 1965/67 352 F100/350's.
All 1968/76 360/390's use the same harmonic balancer, PERIOD: D2TZ6316A.
C3AZ6375L .. 157 Tooth Flexplate.
Marked: C8OP-C / (4) 7/16" converter attaching holes on a 10 1/2" bolt circle / Use with case fill transmissions.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~
EOAZ6375A .. (replaced C5AZ6375T) .. 164 Tooth Flexplate.
(4) converter attaching holes on a 11 7/16" bolt circle / Use with pan fill transmissions.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~
Unrelated to 302/351W's:
1965/76 352/360/390 engines (car/truck) use the same flexplate (C5AZ6375D) with either C-O-M or C6 A/T's.
Some 1965/71 passenger cars w/352/390 engines use a 11" clutch, some use an 11 1/2" clutch.
1965/76 F100/350's 352/360's use an 11" clutch, all 1968/76 F100/350's 390's use an 11 1/2" clutch.
The 352/360 and 390 flywheels can be used either way without any ill effects.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Originally Posted by sparky
My 390 Police Interceptor has a heavier crankshaft than a stock 390.
390 crankshafts:
C3AZ6303C = 1962/63 390 P/C & HiPo only.
C4AZ6303G = 1964/65 390 P/C only.
C3AZ6303B = 1961/63 390 (use before 11/1/1962)
C4AZ6303F = 1963/65 390 (use after 11/1/1962)
C6AZ6303A = 1966/76 390.
~~~~~~~~~~~~~~~~~
ALL 1963/67 352/390's except HiPo's use the same harmonic balancer whether a Police Cruiser or not:
C3AZ6312E. This includes 1965/67 352 F100/350's.
All 1968/76 360/390's use the same harmonic balancer, PERIOD: D2TZ6316A.
Post Fiend
Joined: May 2008
Posts: 7,641
Likes: 21
From: Poway, Ca.
That's good stuff Bill! 
My 390PI is a 65. What I replaced was a 74 390. So, I see you put:
"ALL 1963/67 352/390's except HiPo's use the same harmonic balancer whether a Police Cruiser or not:
C3AZ6312E. This includes 1965/67 352 F100/350's.
All 1968/76 360/390's use the same harmonic balancer, PERIOD: D2TZ6316A."
My old one was shot so we bought a new one anyway, but I was correct in changing out the balance in the transition, right?
Guess I left out a few minor details that weren't really necessary in this example, because as I stated I was speaking (Bold, Italic, Underlined) "Theoretically". Trying to pass on an "IDEA" - you know "PAINT A PICTURE" not dot "i's" and cross "t's." Please forgive me!
It's like learning Algebra: you can try to understand it or you can just memorize it. Chances are if you analyze and understand it you will retain it....See......L*E*A*R*N*I*N*G!!!!
But it's always nice to get the additional details to support what I said. I'm excited! I guess I did that right!
Thanks
Julie
My 390PI is a 65. What I replaced was a 74 390. So, I see you put:
"ALL 1963/67 352/390's except HiPo's use the same harmonic balancer whether a Police Cruiser or not:
C3AZ6312E. This includes 1965/67 352 F100/350's.
All 1968/76 360/390's use the same harmonic balancer, PERIOD: D2TZ6316A."
My old one was shot so we bought a new one anyway, but I was correct in changing out the balance in the transition, right?
Guess I left out a few minor details that weren't really necessary in this example, because as I stated I was speaking (Bold, Italic, Underlined) "Theoretically". Trying to pass on an "IDEA" - you know "PAINT A PICTURE" not dot "i's" and cross "t's." Please forgive me!
It's like learning Algebra: you can try to understand it or you can just memorize it. Chances are if you analyze and understand it you will retain it....See......L*E*A*R*N*I*N*G!!!!
But it's always nice to get the additional details to support what I said. I'm excited! I guess I did that right!
Thanks
Julie
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
Likes: 784
From: Simi Valley, CA
That's good stuff Bill!
My 390PI is a 65. What I replaced was a 74 390. So, I see you put:
"ALL 1963/67 352/390's except HiPo's use the same harmonic balancer whether a Police Cruiser or not:
C3AZ6312E. This includes 1965/67 352 F100/350's.
All 1968/76 360/390's use the same harmonic balancer, PERIOD: D2TZ6316A."
My old one was shot so we bought a new one anyway, but I was correct in changing out the balance in the transition, right?Julie
My 390PI is a 65. What I replaced was a 74 390. So, I see you put:
"ALL 1963/67 352/390's except HiPo's use the same harmonic balancer whether a Police Cruiser or not:
C3AZ6312E. This includes 1965/67 352 F100/350's.
All 1968/76 360/390's use the same harmonic balancer, PERIOD: D2TZ6316A."
My old one was shot so we bought a new one anyway, but I was correct in changing out the balance in the transition, right?Julie
C3AZ6312E .. Harmonic Balancer, which has been repopped, btw.
----------------------------------------------------------------
Cars: 1968/71 390 & 1968/70 428's (except S/CJ).
1968/76 F100/350 360/390:
D2TZ6316A .. Harmonic Balancer
--------------------------------
Note: 1966/67 Merc 410's and 1966/70 Ford/Merc 428's use a different flywheel or flexplate than other FE engines used.
Post Fiend
Joined: May 2008
Posts: 7,641
Likes: 21
From: Poway, Ca.
All: 1960 (not 1963) thru 1967 352/390's (except HiPo's) / All: 1961/65 P/C aka P/I / 1966/67 410/428's (except 428 P/C):
C3AZ6312E .. Harmonic Balancer, which has been repopped, btw.
----------------------------------------------------------------
Cars: 1968/71 390 & 1968/70 428's (except S/CJ).
1968/76 F100/350 360/390:
D2TZ6316A .. Harmonic Balancer
--------------------------------
Note: 1966/67 Merc 410's and 1966/70 Ford/Merc 428's use a different flywheel or flexplate than other FE engines used.
C3AZ6312E .. Harmonic Balancer, which has been repopped, btw.
----------------------------------------------------------------
Cars: 1968/71 390 & 1968/70 428's (except S/CJ).
1968/76 F100/350 360/390:
D2TZ6316A .. Harmonic Balancer
--------------------------------
Note: 1966/67 Merc 410's and 1966/70 Ford/Merc 428's use a different flywheel or flexplate than other FE engines used.
Right, so I had a D2TZ6316A on the old one the 74 390, and I put a C3AZ6312E on the new one the 65 390PI. But the old one was really the new one and about that new one which was really the old one it was broken so.... "I don't know - third base!"
J!
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Posting Guru
Joined: Jun 1999
Posts: 2,415
Likes: 3
From: Comox Valley, Canada
Ok so I have been reading this post, and some others, kind of bored at work
So............. Lets say a guy has a complete running 75 351W with a C6..... and he also has a fairly complete 88 mustang GT parts car with a good 5 speed and a dead 302.... and he also has an 85 351W crank/balancer and most other internals in a box....
So if this guy, who has way too much stuff in his garage and is bored, wanted to build a 351W/5 speed setup to replace the 70 302/FMX setup in his 53 how would he assemble all the afore mentioned parts to get the 351W/5 Speed ready to install in his 53 from a balance point of view..............
Not too shabby at "mechanicing" just a little soft on the mix/match of 302's and 351W's :-)
So............. Lets say a guy has a complete running 75 351W with a C6..... and he also has a fairly complete 88 mustang GT parts car with a good 5 speed and a dead 302.... and he also has an 85 351W crank/balancer and most other internals in a box....
So if this guy, who has way too much stuff in his garage and is bored, wanted to build a 351W/5 speed setup to replace the 70 302/FMX setup in his 53 how would he assemble all the afore mentioned parts to get the 351W/5 Speed ready to install in his 53 from a balance point of view..............
Not too shabby at "mechanicing" just a little soft on the mix/match of 302's and 351W's :-)
Posting Guru
Joined: Jun 1999
Posts: 2,415
Likes: 3
From: Comox Valley, Canada
also has a 79 Mustang with a dead 302 and a 4 speed in his parts pile he could use the tranny/flywheel from this one and bolt it to the 75 351W and all would be balanced in his world..........except he would be missing one gear.......and a few screws or he should be able to use the 79 flywheel and the 88 tranny........ or he could give in to his wife and get rid of his "excess" amount of stuff..... but he can't see that happening anytime soon 
I'll have the Roast Duck
Joined: Jul 2002
Posts: 9,622
Likes: 109
From: Northshore, MN
In theory, the 79 302 flywheel (28 oz) should bolt onto the 351W, and the 88 T5 should bolt onto that, provided the flywheels from the 79 and 88 are the same diameter and tooth count to match the 88's starter that bolts to the 88's bellhousing. Clear as mud?
FWIW, that 4 speed might have OD. Do you have the RAD?ROD?RUG number on the tag handy? I have a 79 4 speed all aluminum sitting out back too. no OD, though.
FWIW, that 4 speed might have OD. Do you have the RAD?ROD?RUG number on the tag handy? I have a 79 4 speed all aluminum sitting out back too. no OD, though.
Post Fiend
Joined: May 2008
Posts: 7,641
Likes: 21
From: Poway, Ca.
So if this guy who had too much stuff got in the vehicle with the 351w/C6, left Comox Valley and headed south at 125 KPH and his wife took of after him in the 79 mustang with the dead 302 being hauled away at 65 MPH by AAA, how long would it take her to catch up with him to run him over and who would get the 53 F-100 when she gets arrested in Washington?
J!
J!
Posting Guru
Joined: Jan 2008
Posts: 2,138
Likes: 2
From: Marietta, Ohio
I'm still trying to figure out how any flywheel is going to weigh 28 0z. A flexplate w/ring gear, maybe,,, But I can't imagine a flywheel being that light.
Obviously I'm missing something here...
And Julie... You left out part of the equation. Did the guy with the extra parts leave his Rotweiler locked in the garage when he left???