Flywheel compatability

Joined
Feb 23, 2012
Messages
1
Likes
0
Points
0
#1
1978 Ford F150

Does the flywheel for a 351M interchange with a 400M?


Thanks in advance!
 

jasonn20

Hero Member
Joined
Oct 28, 2008
Messages
308
Likes
1
Points
0
#2
you should get the correct flywheel as engine needs a neutral balance (harmonics) and if you get the incorrect weigh it makes bearings wear out quicker.
 

billr

wrench
Staff member
Joined
Mar 12, 2007
Messages
5,995
Likes
60
Points
48
#3
I'm just guessing, but I would expect that the 400, being a "stroked" small-block, has to have external balancing out on the flywheel; not enough room in the crankcase for proper counter-weights. So the flywheel wouldn't be interchangeable with another displacement.
 
Joined
Aug 28, 2007
Messages
4,699
Likes
18
Points
38
#4
Flywheel or a flexplate, F-150 comes with either, new flexplate is only around 30 bucks.



But only can seem to find a 13 buck ring gear for the flywheel.



Replaced the flexplate when I rebuilt my TH-400 mainly to get a new ring gear, but kept the old one for a side by side comparison. Putting the whole thing back together is not the time to find the replacement flexplate has an extra tooth in it or a 1/32" larger in diameter where the starter drive will crash into it.

Could be your terminology is correct and you do have a manual transmission, but even with other engineers, always had a problem with terminology, have to be very specific if you want the correct answer. Even NASA screwed up, one guy was talking inches, other was talking centimeters.
 
Joined
Nov 14, 2006
Messages
1,226
Likes
0
Points
36
Age
118
Location
enderby british columbia canada
#5
351m and 400m are the same block.both big blocks.they are both balanced the same so balance shouldnt be a problem.i would check to make sure flywheel depth is the same for both flywheels.ford had a habit of making little changes like that back in the day.final authority on this one is your local wrecking yard and their interchange book.
 

billr

wrench
Staff member
Joined
Mar 12, 2007
Messages
5,995
Likes
60
Points
48
#6
Are you sure, Al?

I'm no expert on old Ford V-8s, but the info I read says the 351M and 400M are both "raised deck" versions of the Cleveland small-block (351C). At any rate, they may still use different balancing since the cranks are different.
 
Joined
Nov 14, 2006
Messages
1,226
Likes
0
Points
36
Age
118
Location
enderby british columbia canada
#7
we allways called them modified or big blocks.the correct term would be modified block.both are raised block versions of the 350 cleveland.351m and 400m are both balanced the same and is far as i remember had identical flywheels.like i said,the autowrecker would have the final say here.