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  1. #1
    Join Date
    Nov 2007
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    northants
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    93

    351w 7M crank balance, 50oz?

    Anyone know if the 7M 351w crank is balanced at 50oz rather than 28oz?
    Google is not providing an answer.
    Engine came as several boxes of bits, but balancer looks like 50oz type. Trying to figure what flywheel balance I need. D code block, but with later crank by seem off things.
    Thanks in advance.
    David

  2. #2
    Join Date
    May 2011
    Location
    Flimwell
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    866
    All 351s are 28oz external balance unless they’ve been heavily modified. (Non-standard crank perhaps).

  3. #3
    Join Date
    Nov 2007
    Location
    northants
    Posts
    93
    Well I thought that, but I am sure I read somewhere late 351w cranks were cast heavier, for less flex, at 50oz. Can I find where I read it, of which revision of the crank. 6M 7M 7MA... Why did they have to go confuse things...

  4. #4
    Join Date
    Sep 2010
    Location
    Nova Scotia
    Posts
    945
    It appears you remember correctly. Summit lists the 28 ox flywheel for years 1968-1981 and the 50 oz flywheel for years 1986-1991. Not sure about years in between. My Ford Parts Interchange book, which is reputedly full of errors, states the heavier weight started in 1985.

    Best not to trust any of this, but it may help a bit. Even though it cost a bit, I'd have the rotating assembly balanced. Any errors would be detected and corrected at that time. I had that done for my 428 Fe that uses external balance. That was a long time ago, but seems to me it was less than $300 Cdn... back in 1996.
    John

    “A prudent person profits from personal experience, a wise one from the experience of others.”

  5. #5
    Join Date
    Nov 2007
    Location
    northants
    Posts
    93
    Just found this
    When the 351W engine was upgraded to a onepiece rear main seal in 1985, its revised nodular iron crankshaft received a revised “7M” identification code. Later in production, it was identified as “7MA.”

    So it seems it is likely my crank is post 1985 and 50oz, so new balancer, as old one is coming apart :0
    and a 50oz flywheel.
    Crank has an E part number which places it in the 80's I guess and so fits in. Balancer also E part number. Everything else 1970 D coded.

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